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[PATCH v2] Track skipped tables during vacuum and analyze
211+ messages / 2 participants
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* [PATCH v2] Track skipped tables during vacuum and analyze
@ 2026-03-24 04:09 Yugo Nagata <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Yugo Nagata @ 2026-03-24 04:09 UTC (permalink / raw)

---
 src/backend/catalog/system_views.sql         |  8 ++
 src/backend/commands/vacuum.c                | 84 +++++++++++++++-----
 src/backend/utils/activity/pgstat_relation.c | 69 ++++++++++++++++
 src/backend/utils/adt/pgstatfuncs.c          | 24 ++++++
 src/include/catalog/pg_proc.dat              | 32 ++++++++
 src/include/pgstat.h                         | 11 +++
 src/test/regress/expected/rules.out          | 24 ++++++
 7 files changed, 230 insertions(+), 22 deletions(-)

diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index e54018004db..2ca02a0354c 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -736,13 +736,21 @@ CREATE VIEW pg_stat_all_tables AS
             pg_stat_get_mod_since_analyze(C.oid) AS n_mod_since_analyze,
             pg_stat_get_ins_since_vacuum(C.oid) AS n_ins_since_vacuum,
             pg_stat_get_last_vacuum_time(C.oid) as last_vacuum,
+            pg_stat_get_last_skipped_vacuum_time(C.oid) as last_skipped_vacuum,
             pg_stat_get_last_autovacuum_time(C.oid) as last_autovacuum,
+            pg_stat_get_last_skipped_autovacuum_time(C.oid) as last_skipped_autovacuum,
             pg_stat_get_last_analyze_time(C.oid) as last_analyze,
+            pg_stat_get_last_skipped_analyze_time(C.oid) as last_skipped_analyze,
             pg_stat_get_last_autoanalyze_time(C.oid) as last_autoanalyze,
+            pg_stat_get_last_skipped_autoanalyze_time(C.oid) as last_skipped_autoanalyze,
             pg_stat_get_vacuum_count(C.oid) AS vacuum_count,
+            pg_stat_get_skipped_vacuum_count(C.oid) AS skipped_vacuum_count,
             pg_stat_get_autovacuum_count(C.oid) AS autovacuum_count,
+            pg_stat_get_skipped_autovacuum_count(C.oid) AS skipped_autovacuum_count,
             pg_stat_get_analyze_count(C.oid) AS analyze_count,
+            pg_stat_get_skipped_analyze_count(C.oid) AS skipped_analyze_count,
             pg_stat_get_autoanalyze_count(C.oid) AS autoanalyze_count,
+            pg_stat_get_skipped_autoanalyze_count(C.oid) AS skipped_autoanalyze_count,
             pg_stat_get_total_vacuum_time(C.oid) AS total_vacuum_time,
             pg_stat_get_total_autovacuum_time(C.oid) AS total_autovacuum_time,
             pg_stat_get_total_analyze_time(C.oid) AS total_analyze_time,
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index bce3a2daa24..8125dfac137 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -794,6 +794,11 @@ vacuum_open_relation(Oid relid, RangeVar *relation, bits32 options,
 	{
 		rel = NULL;
 		rel_lock = false;
+
+		pgstat_report_skipped_vacuum_analyze(relid,
+											 (options & VACOPT_VACUUM) != 0,
+											 (options & VACOPT_ANALYZE) != 0,
+											 AmAutoVacuumWorkerProcess());
 	}
 
 	/* if relation is opened, leave */
@@ -904,7 +909,6 @@ expand_vacuum_rel(VacuumRelation *vrel, MemoryContext vac_context,
 		Form_pg_class classForm;
 		bool		include_children;
 		bool		is_partitioned_table;
-		int			rvr_opts;
 
 		/*
 		 * Since autovacuum workers supply OIDs when calling vacuum(), no
@@ -917,29 +921,65 @@ expand_vacuum_rel(VacuumRelation *vrel, MemoryContext vac_context,
 		 * below, as well as find_all_inheritors's expectation that the caller
 		 * holds some lock on the starting relation.
 		 */
-		rvr_opts = (options & VACOPT_SKIP_LOCKED) ? RVR_SKIP_LOCKED : 0;
-		relid = RangeVarGetRelidExtended(vrel->relation,
-										 AccessShareLock,
-										 rvr_opts,
-										 NULL, NULL);
-
-		/*
-		 * If the lock is unavailable, emit the same log statement that
-		 * vacuum_rel() and analyze_rel() would.
-		 */
-		if (!OidIsValid(relid))
+		if (!(options & VACOPT_SKIP_LOCKED))
 		{
-			if (options & VACOPT_VACUUM)
-				ereport(WARNING,
-						(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
-						 errmsg("skipping vacuum of \"%s\" --- lock not available",
-								vrel->relation->relname)));
-			else
-				ereport(WARNING,
-						(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
-						 errmsg("skipping analyze of \"%s\" --- lock not available",
+			relid = RangeVarGetRelidExtended(vrel->relation,
+											 AccessShareLock,
+											 0, NULL, NULL);
+			if (!OidIsValid(relid))
+				return vacrels;
+		}
+		else
+		{
+			/* Get relid for reporting before taking a lock */
+			relid = RangeVarGetRelid(vrel->relation, NoLock, false);
+
+			if (!ConditionalLockRelationOid(relid, AccessShareLock))
+			{
+				/*
+				 * If the lock is unavailable, emit the same log statement that
+				 * vacuum_rel() and analyze_rel() would.
+				 */
+				if (options & VACOPT_VACUUM)
+					ereport(WARNING,
+							(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+							 errmsg("skipping vacuum of \"%s\" --- lock not available",
 								vrel->relation->relname)));
-			return vacrels;
+				else
+					ereport(WARNING,
+							(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
+							 errmsg("skipping analyze of \"%s\" --- lock not available",
+									vrel->relation->relname)));
+
+				pgstat_report_skipped_vacuum_analyze(relid,
+													 (options & VACOPT_VACUUM) != 0,
+													 (options & VACOPT_ANALYZE) != 0,
+													 false);
+				return vacrels;
+			}
+
+			/*
+			 * Now that we have the lock, probe to see if the relation really
+			 * exists or not.
+			 */
+			if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(relid)))
+			{
+				if (options & VACOPT_VACUUM)
+					ereport(WARNING,
+							(errcode(ERRCODE_UNDEFINED_TABLE),
+							 errmsg("skipping vacuum of \"%s\" --- relation no longer exists",
+									vrel->relation->relname)));
+				else
+					ereport(WARNING,
+							(errcode(ERRCODE_UNDEFINED_TABLE),
+							 errmsg("skipping analyze of \"%s\" --- relation no longer exists",
+									vrel->relation->relname)));
+
+				/* Release useless lock */
+				UnlockRelationOid(relid, AccessShareLock);
+
+				return vacrels;
+			}
 		}
 
 		/*
diff --git a/src/backend/utils/activity/pgstat_relation.c b/src/backend/utils/activity/pgstat_relation.c
index bc8c43b96aa..51d0f280ebf 100644
--- a/src/backend/utils/activity/pgstat_relation.c
+++ b/src/backend/utils/activity/pgstat_relation.c
@@ -17,6 +17,7 @@
 
 #include "postgres.h"
 
+#include "access/htup_details.h"
 #include "access/twophase_rmgr.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
@@ -366,6 +367,74 @@ pgstat_report_analyze(Relation rel,
 	(void) pgstat_flush_backend(false, PGSTAT_BACKEND_FLUSH_IO);
 }
 
+/*
+ * Report that the table was skipped during vacuum or/and analyze.
+ */
+void
+pgstat_report_skipped_vacuum_analyze(Oid relid, bool vacuum, bool analyze,
+									 bool autovacuum)
+{
+	PgStat_EntryRef *entry_ref;
+	PgStatShared_Relation *shtabentry;
+	PgStat_StatTabEntry *tabentry;
+	TimestampTz ts;
+	HeapTuple	classTup;
+	bool		isshared;
+
+	if (!pgstat_track_counts || !(vacuum || analyze))
+		return;
+
+	classTup = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
+	if (!HeapTupleIsValid(classTup))
+		return;			/* somebody deleted the rel, forget it */
+	isshared = ((Form_pg_class) GETSTRUCT(classTup))->relisshared;
+	ReleaseSysCache(classTup);
+
+	/* Store the data in the table's hash table entry. */
+	ts = GetCurrentTimestamp();
+
+	/* block acquiring lock for the same reason as pgstat_report_autovac() */
+	entry_ref = pgstat_get_entry_ref_locked(PGSTAT_KIND_RELATION,
+											isshared ? InvalidOid : MyDatabaseId,
+											relid, false);
+
+	shtabentry = (PgStatShared_Relation *) entry_ref->shared_stats;
+	tabentry = &shtabentry->stats;
+
+	if (autovacuum)
+	{
+		if (vacuum)
+		{
+			tabentry->last_skipped_autovacuum_time = ts;
+			tabentry->skipped_autovacuum_count++;
+		}
+		if (analyze)
+		{
+			tabentry->last_skipped_autoanalyze_time = ts;
+			tabentry->skipped_autoanalyze_count++;
+		}
+	}
+	else
+	{
+		if (vacuum)
+		{
+			tabentry->last_skipped_vacuum_time = ts;
+			tabentry->skipped_vacuum_count++;
+		}
+		if (analyze)
+		{
+			tabentry->last_skipped_analyze_time = ts;
+			tabentry->skipped_analyze_count++;
+		}
+	}
+
+	pgstat_unlock_entry(entry_ref);
+
+	/* see pgstat_report_vacuum() */
+	pgstat_flush_io(false);
+	(void) pgstat_flush_backend(false, PGSTAT_BACKEND_FLUSH_IO);
+}
+
 /*
  * count a tuple insertion of n tuples
  */
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 9185a8e6b83..18aaa3996e1 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -84,6 +84,18 @@ PG_STAT_GET_RELENTRY_INT64(mod_since_analyze)
 /* pg_stat_get_numscans */
 PG_STAT_GET_RELENTRY_INT64(numscans)
 
+/* pg_stat_get_skipped_analyze_count */
+PG_STAT_GET_RELENTRY_INT64(skipped_analyze_count)
+
+/* pg_stat_get_skipped_autoanalyze_count */
+PG_STAT_GET_RELENTRY_INT64(skipped_autoanalyze_count)
+
+/* pg_stat_get_skipped_autovacuum_count */
+PG_STAT_GET_RELENTRY_INT64(skipped_autovacuum_count)
+
+/* pg_stat_get_skipped_vacuum_count */
+PG_STAT_GET_RELENTRY_INT64(skipped_vacuum_count)
+
 /* pg_stat_get_tuples_deleted */
 PG_STAT_GET_RELENTRY_INT64(tuples_deleted)
 
@@ -170,6 +182,18 @@ PG_STAT_GET_RELENTRY_TIMESTAMPTZ(last_vacuum_time)
 /* pg_stat_get_lastscan */
 PG_STAT_GET_RELENTRY_TIMESTAMPTZ(lastscan)
 
+/* pg_stat_get_last_skipped_analyze_time */
+PG_STAT_GET_RELENTRY_TIMESTAMPTZ(last_skipped_analyze_time)
+
+/* pg_stat_get_last_skipped_autoanalyze_time */
+PG_STAT_GET_RELENTRY_TIMESTAMPTZ(last_skipped_autoanalyze_time)
+
+/* pg_stat_get_last_skipped_autovacuum_time */
+PG_STAT_GET_RELENTRY_TIMESTAMPTZ(last_skipped_autovacuum_time)
+
+/* pg_stat_get_last_skipped_vacuum_time */
+PG_STAT_GET_RELENTRY_TIMESTAMPTZ(last_skipped_vacuum_time)
+
 /* pg_stat_get_stat_reset_time */
 PG_STAT_GET_RELENTRY_TIMESTAMPTZ(stat_reset_time)
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 0118e970dda..ccfe3d9e02a 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5667,6 +5667,38 @@
   proname => 'pg_stat_get_total_autoanalyze_time', provolatile => 's',
   proparallel => 'r', prorettype => 'float8', proargtypes => 'oid',
   prosrc => 'pg_stat_get_total_autoanalyze_time' },
+{ oid => '8142', descr => 'statistics: last skipped vacuum time for a table',
+  proname => 'pg_stat_get_last_skipped_vacuum_time', provolatile => 's',
+  proparallel => 'r', prorettype => 'timestamptz', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_last_skipped_vacuum_time' },
+{ oid => '8143', descr => 'statistics: last skipped auto vacuum time for a table',
+  proname => 'pg_stat_get_last_skipped_autovacuum_time', provolatile => 's',
+  proparallel => 'r', prorettype => 'timestamptz', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_last_skipped_autovacuum_time' },
+{ oid => '8144', descr => 'statistics: last skipped analyze time for a table',
+  proname => 'pg_stat_get_last_skipped_analyze_time', provolatile => 's',
+  proparallel => 'r', prorettype => 'timestamptz', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_last_skipped_analyze_time' },
+{ oid => '8145', descr => 'statistics: last skipped auto analyze time for a table',
+  proname => 'pg_stat_get_last_skipped_autoanalyze_time', provolatile => 's',
+  proparallel => 'r', prorettype => 'timestamptz', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_last_skipped_autoanalyze_time' },
+{ oid => '8146', descr => 'statistics: number of skipped vacuum for a table',
+  proname => 'pg_stat_get_skipped_vacuum_count', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_skipped_vacuum_count' },
+{ oid => '8147', descr => 'statistics: number of skipped auto vacuum for a table',
+  proname => 'pg_stat_get_skipped_autovacuum_count', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_skipped_autovacuum_count' },
+{ oid => '8148', descr => 'statistics: number of skipped analyzes for a table',
+  proname => 'pg_stat_get_skipped_analyze_count', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_skipped_analyze_count' },
+{ oid => '8149', descr => 'statistics: number of skipped auto analyzes for a table',
+  proname => 'pg_stat_get_skipped_autoanalyze_count', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
+  prosrc => 'pg_stat_get_skipped_autoanalyze_count' },
 { oid => '1936', descr => 'statistics: currently active backend IDs',
   proname => 'pg_stat_get_backend_idset', prorows => '100', proretset => 't',
   provolatile => 's', proparallel => 'r', prorettype => 'int4',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 8e3549c3752..d7f19d91783 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -479,6 +479,15 @@ typedef struct PgStat_StatTabEntry
 	TimestampTz last_autoanalyze_time;	/* autovacuum initiated */
 	PgStat_Counter autoanalyze_count;
 
+	TimestampTz last_skipped_vacuum_time;	/* user initiated vacuum */
+	PgStat_Counter skipped_vacuum_count;
+	TimestampTz last_skipped_autovacuum_time;	/* autovacuum initiated */
+	PgStat_Counter skipped_autovacuum_count;
+	TimestampTz last_skipped_analyze_time;	/* user initiated */
+	PgStat_Counter skipped_analyze_count;
+	TimestampTz last_skipped_autoanalyze_time;	/* autovacuum initiated */
+	PgStat_Counter skipped_autoanalyze_count;
+
 	PgStat_Counter total_vacuum_time;	/* times in milliseconds */
 	PgStat_Counter total_autovacuum_time;
 	PgStat_Counter total_analyze_time;
@@ -706,6 +715,8 @@ extern void pgstat_report_vacuum(Relation rel, PgStat_Counter livetuples,
 extern void pgstat_report_analyze(Relation rel,
 								  PgStat_Counter livetuples, PgStat_Counter deadtuples,
 								  bool resetcounter, TimestampTz starttime);
+extern void pgstat_report_skipped_vacuum_analyze(Oid relid, bool vacuum, bool analyze,
+												 bool autovacuum);
 
 /*
  * If stats are enabled, but pending data hasn't been prepared yet, call
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 2b3cf6d8569..4ccfc43e903 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1835,13 +1835,21 @@ pg_stat_all_tables| SELECT c.oid AS relid,
     pg_stat_get_mod_since_analyze(c.oid) AS n_mod_since_analyze,
     pg_stat_get_ins_since_vacuum(c.oid) AS n_ins_since_vacuum,
     pg_stat_get_last_vacuum_time(c.oid) AS last_vacuum,
+    pg_stat_get_last_skipped_vacuum_time(c.oid) AS last_skipped_vacuum,
     pg_stat_get_last_autovacuum_time(c.oid) AS last_autovacuum,
+    pg_stat_get_last_skipped_autovacuum_time(c.oid) AS last_skipped_autovacuum,
     pg_stat_get_last_analyze_time(c.oid) AS last_analyze,
+    pg_stat_get_last_skipped_analyze_time(c.oid) AS last_skipped_analyze,
     pg_stat_get_last_autoanalyze_time(c.oid) AS last_autoanalyze,
+    pg_stat_get_last_skipped_autoanalyze_time(c.oid) AS last_skipped_autoanalyze,
     pg_stat_get_vacuum_count(c.oid) AS vacuum_count,
+    pg_stat_get_skipped_vacuum_count(c.oid) AS skipped_vacuum_count,
     pg_stat_get_autovacuum_count(c.oid) AS autovacuum_count,
+    pg_stat_get_skipped_autovacuum_count(c.oid) AS skipped_autovacuum_count,
     pg_stat_get_analyze_count(c.oid) AS analyze_count,
+    pg_stat_get_skipped_analyze_count(c.oid) AS skipped_analyze_count,
     pg_stat_get_autoanalyze_count(c.oid) AS autoanalyze_count,
+    pg_stat_get_skipped_autoanalyze_count(c.oid) AS skipped_autoanalyze_count,
     pg_stat_get_total_vacuum_time(c.oid) AS total_vacuum_time,
     pg_stat_get_total_autovacuum_time(c.oid) AS total_autovacuum_time,
     pg_stat_get_total_analyze_time(c.oid) AS total_analyze_time,
@@ -2293,13 +2301,21 @@ pg_stat_sys_tables| SELECT relid,
     n_mod_since_analyze,
     n_ins_since_vacuum,
     last_vacuum,
+    last_skipped_vacuum,
     last_autovacuum,
+    last_skipped_autovacuum,
     last_analyze,
+    last_skipped_analyze,
     last_autoanalyze,
+    last_skipped_autoanalyze,
     vacuum_count,
+    skipped_vacuum_count,
     autovacuum_count,
+    skipped_autovacuum_count,
     analyze_count,
+    skipped_analyze_count,
     autoanalyze_count,
+    skipped_autoanalyze_count,
     total_vacuum_time,
     total_autovacuum_time,
     total_analyze_time,
@@ -2348,13 +2364,21 @@ pg_stat_user_tables| SELECT relid,
     n_mod_since_analyze,
     n_ins_since_vacuum,
     last_vacuum,
+    last_skipped_vacuum,
     last_autovacuum,
+    last_skipped_autovacuum,
     last_analyze,
+    last_skipped_analyze,
     last_autoanalyze,
+    last_skipped_autoanalyze,
     vacuum_count,
+    skipped_vacuum_count,
     autovacuum_count,
+    skipped_autovacuum_count,
     analyze_count,
+    skipped_analyze_count,
     autoanalyze_count,
+    skipped_autoanalyze_count,
     total_vacuum_time,
     total_autovacuum_time,
     total_analyze_time,
-- 
2.43.0


--Multipart=_Thu__26_Mar_2026_19_22_03_+0900_+1+LQ8ruMpR+Xuy_--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


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Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v56 2/3] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 84 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 +++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 116 insertions(+), 62 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3324d2d3c49..3435732646e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4639,6 +4639,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 17b639b3b44..5e97fcf3818 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3357,7 +3357,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 94d034970b5..ea330310e27 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -212,7 +212,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -221,8 +221,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -233,6 +233,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 9e75a3e04ee..7adf4dbe0d1 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 8ceaf64d164..d8e02c53558 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -304,6 +304,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -324,6 +325,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -340,7 +342,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index 8b53bd3ac7f..ae900f13467 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -434,7 +434,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -823,6 +823,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1707,7 +1708,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a1f37e59dbc..e6722fc0212 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -160,6 +160,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -199,12 +201,13 @@ ReplicationSlotsShmemRequest(void *arg)
 {
 	Size		size;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(max_replication_slots + max_repack_replication_slots,
+							 sizeof(ReplicationSlot)));
 	ShmemRequestStruct(.name = "ReplicationSlot Ctl",
 					   .size = size,
 					   .ptr = (void **) &ReplicationSlotCtl,
@@ -217,7 +220,7 @@ ReplicationSlotsShmemRequest(void *arg)
 static void
 ReplicationSlotsShmemInit(void *arg)
 {
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -366,6 +369,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -373,10 +377,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -425,12 +430,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -438,7 +447,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -448,7 +459,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -541,7 +553,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -569,7 +581,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -863,7 +876,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1245,7 +1258,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1300,7 +1313,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1367,12 +1380,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1447,11 +1460,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1508,13 +1521,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1611,11 +1624,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1649,17 +1662,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2210,7 +2230,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2218,7 +2238,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2323,7 +2343,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2424,7 +2444,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index b4a2117a7f9..bad45adb004 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1241,7 +1241,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1261,7 +1261,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1272,7 +1272,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1330,6 +1330,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1487,7 +1488,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fcb6ab80583..632f3ba4989 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2079,6 +2079,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e3e462f3efb..2e10eb4a36a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1a3557de607..77c8d0975b6 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,13 +324,14 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -373,7 +374,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v56-0003-Error-out-any-process-that-would-block-at-REPACK.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v56 2/3] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 84 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 +++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 116 insertions(+), 62 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3324d2d3c49..3435732646e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4639,6 +4639,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 17b639b3b44..5e97fcf3818 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3357,7 +3357,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 94d034970b5..ea330310e27 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -212,7 +212,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -221,8 +221,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -233,6 +233,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 9e75a3e04ee..7adf4dbe0d1 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 8ceaf64d164..d8e02c53558 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -304,6 +304,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -324,6 +325,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -340,7 +342,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index 8b53bd3ac7f..ae900f13467 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -434,7 +434,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -823,6 +823,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1707,7 +1708,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a1f37e59dbc..e6722fc0212 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -160,6 +160,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -199,12 +201,13 @@ ReplicationSlotsShmemRequest(void *arg)
 {
 	Size		size;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(max_replication_slots + max_repack_replication_slots,
+							 sizeof(ReplicationSlot)));
 	ShmemRequestStruct(.name = "ReplicationSlot Ctl",
 					   .size = size,
 					   .ptr = (void **) &ReplicationSlotCtl,
@@ -217,7 +220,7 @@ ReplicationSlotsShmemRequest(void *arg)
 static void
 ReplicationSlotsShmemInit(void *arg)
 {
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -366,6 +369,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -373,10 +377,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -425,12 +430,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -438,7 +447,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -448,7 +459,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -541,7 +553,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -569,7 +581,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -863,7 +876,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1245,7 +1258,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1300,7 +1313,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1367,12 +1380,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1447,11 +1460,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1508,13 +1521,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1611,11 +1624,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1649,17 +1662,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2210,7 +2230,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2218,7 +2238,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2323,7 +2343,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2424,7 +2444,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index b4a2117a7f9..bad45adb004 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1241,7 +1241,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1261,7 +1261,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1272,7 +1272,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1330,6 +1330,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1487,7 +1488,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fcb6ab80583..632f3ba4989 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2079,6 +2079,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e3e462f3efb..2e10eb4a36a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1a3557de607..77c8d0975b6 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,13 +324,14 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -373,7 +374,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v56-0003-Error-out-any-process-that-would-block-at-REPACK.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 211+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 211+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





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