agora inbox for pgsql-hackers@postgresql.org  

help / color / mirror / Atom feed

[PATCH v18 1/8] Row pattern recognition patch for raw parser.
452+ messages / 2 participants
[nested] [flat]

* [PATCH v18 1/8] Row pattern recognition patch for raw parser.
@ 2024-05-11 07:11  Tatsuo Ishii <ishii@postgresql.org>
  0 siblings, 0 replies; 452+ messages in thread

From: Tatsuo Ishii @ 2024-05-11 07:11 UTC (permalink / raw)

---
 src/backend/parser/gram.y       | 221 ++++++++++++++++++++++++++++++--
 src/include/nodes/parsenodes.h  |  67 ++++++++++
 src/include/parser/kwlist.h     |   8 ++
 src/include/parser/parse_node.h |   1 +
 4 files changed, 285 insertions(+), 12 deletions(-)

diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index e8b619926e..c09a0f7e4f 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -680,6 +680,21 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 				json_object_constructor_null_clause_opt
 				json_array_constructor_null_clause_opt
 
+%type <target>	row_pattern_measure_item
+				row_pattern_definition
+%type <node>	opt_row_pattern_common_syntax
+				opt_row_pattern_skip_to
+				row_pattern_subset_item
+				row_pattern_term
+%type <list>	opt_row_pattern_measures
+				row_pattern_measure_list
+				row_pattern_definition_list
+				opt_row_pattern_subset_clause
+				row_pattern_subset_list
+				row_pattern_subset_rhs
+				row_pattern
+%type <boolean>	opt_row_pattern_initial_or_seek
+				first_or_last
 
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
@@ -723,7 +738,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	CURRENT_TIME CURRENT_TIMESTAMP CURRENT_USER CURSOR CYCLE
 
 	DATA_P DATABASE DAY_P DEALLOCATE DEC DECIMAL_P DECLARE DEFAULT DEFAULTS
-	DEFERRABLE DEFERRED DEFINER DELETE_P DELIMITER DELIMITERS DEPENDS DEPTH DESC
+	DEFERRABLE DEFERRED DEFINE DEFINER DELETE_P DELIMITER DELIMITERS DEPENDS DEPTH DESC
 	DETACH DICTIONARY DISABLE_P DISCARD DISTINCT DO DOCUMENT_P DOMAIN_P
 	DOUBLE_P DROP
 
@@ -739,7 +754,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	HANDLER HAVING HEADER_P HOLD HOUR_P
 
 	IDENTITY_P IF_P ILIKE IMMEDIATE IMMUTABLE IMPLICIT_P IMPORT_P IN_P INCLUDE
-	INCLUDING INCREMENT INDENT INDEX INDEXES INHERIT INHERITS INITIALLY INLINE_P
+	INCLUDING INCREMENT INDENT INDEX INDEXES INHERIT INHERITS INITIAL INITIALLY INLINE_P
 	INNER_P INOUT INPUT_P INSENSITIVE INSERT INSTEAD INT_P INTEGER
 	INTERSECT INTERVAL INTO INVOKER IS ISNULL ISOLATION
 
@@ -752,7 +767,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	LEADING LEAKPROOF LEAST LEFT LEVEL LIKE LIMIT LISTEN LOAD LOCAL
 	LOCALTIME LOCALTIMESTAMP LOCATION LOCK_P LOCKED LOGGED
 
-	MAPPING MATCH MATCHED MATERIALIZED MAXVALUE MERGE MERGE_ACTION METHOD
+	MAPPING MATCH MATCHED MATERIALIZED MAXVALUE MEASURES MERGE MERGE_ACTION METHOD
 	MINUTE_P MINVALUE MODE MONTH_P MOVE
 
 	NAME_P NAMES NATIONAL NATURAL NCHAR NESTED NEW NEXT NFC NFD NFKC NFKD NO
@@ -764,9 +779,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	ORDER ORDINALITY OTHERS OUT_P OUTER_P
 	OVER OVERLAPS OVERLAY OVERRIDING OWNED OWNER
 
-	PARALLEL PARAMETER PARSER PARTIAL PARTITION PARTITIONS PASSING PASSWORD PATH
-	PERIOD PLACING PLAN PLANS POLICY
-
+	PARALLEL PARAMETER PARSER PARTIAL PARTITION PARTITIONS PASSING PASSWORD PAST
+	PATH PATTERN_P PERIOD PERMUTE PLACING PLAN PLANS POLICY
 	POSITION PRECEDING PRECISION PRESERVE PREPARE PREPARED PRIMARY
 	PRIOR PRIVILEGES PROCEDURAL PROCEDURE PROCEDURES PROGRAM PUBLICATION
 
@@ -777,12 +791,13 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	RESET RESTART RESTRICT RETURN RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROLLUP
 	ROUTINE ROUTINES ROW ROWS RULE
 
-	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SELECT
+	SAVEPOINT SCALAR SCHEMA SCHEMAS SCROLL SEARCH SECOND_P SECURITY SEEK SELECT
 	SEQUENCE SEQUENCES
+
 	SERIALIZABLE SERVER SESSION SESSION_USER SET SETS SETOF SHARE SHOW
 	SIMILAR SIMPLE SKIP SMALLINT SNAPSHOT SOME SPLIT SOURCE SQL_P STABLE STANDALONE_P
 	START STATEMENT STATISTICS STDIN STDOUT STORAGE STORED STRICT_P STRING_P STRIP_P
-	SUBSCRIPTION SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
+	SUBSCRIPTION SUBSET SUBSTRING SUPPORT SYMMETRIC SYSID SYSTEM_P SYSTEM_USER
 
 	TABLE TABLES TABLESAMPLE TABLESPACE TARGET TEMP TEMPLATE TEMPORARY TEXT_P THEN
 	TIES TIME TIMESTAMP TO TRAILING TRANSACTION TRANSFORM
@@ -891,6 +906,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %nonassoc	UNBOUNDED NESTED /* ideally would have same precedence as IDENT */
 %nonassoc	IDENT PARTITION RANGE ROWS GROUPS PRECEDING FOLLOWING CUBE ROLLUP
 			SET KEYS OBJECT_P SCALAR VALUE_P WITH WITHOUT PATH
+			MEASURES AFTER INITIAL SEEK PATTERN_P
 %left		Op OPERATOR		/* multi-character ops and user-defined operators */
 %left		'+' '-'
 %left		'*' '/' '%'
@@ -16333,7 +16349,8 @@ over_clause: OVER window_specification
 		;
 
 window_specification: '(' opt_existing_window_name opt_partition_clause
-						opt_sort_clause opt_frame_clause ')'
+						opt_sort_clause opt_row_pattern_measures opt_frame_clause
+						opt_row_pattern_common_syntax ')'
 				{
 					WindowDef  *n = makeNode(WindowDef);
 
@@ -16341,10 +16358,12 @@ window_specification: '(' opt_existing_window_name opt_partition_clause
 					n->refname = $2;
 					n->partitionClause = $3;
 					n->orderClause = $4;
+					n->rowPatternMeasures = $5;
 					/* copy relevant fields of opt_frame_clause */
-					n->frameOptions = $5->frameOptions;
-					n->startOffset = $5->startOffset;
-					n->endOffset = $5->endOffset;
+					n->frameOptions = $6->frameOptions;
+					n->startOffset = $6->startOffset;
+					n->endOffset = $6->endOffset;
+					n->rpCommonSyntax = (RPCommonSyntax *)$7;
 					n->location = @1;
 					$$ = n;
 				}
@@ -16368,6 +16387,31 @@ opt_partition_clause: PARTITION BY expr_list		{ $$ = $3; }
 			| /*EMPTY*/								{ $$ = NIL; }
 		;
 
+/*
+ * ROW PATTERN_P MEASURES
+ */
+opt_row_pattern_measures: MEASURES row_pattern_measure_list	{ $$ = $2; }
+			| /*EMPTY*/								{ $$ = NIL; }
+		;
+
+row_pattern_measure_list:
+			row_pattern_measure_item
+					{ $$ = list_make1($1); }
+			| row_pattern_measure_list ',' row_pattern_measure_item
+					{ $$ = lappend($1, $3); }
+		;
+
+row_pattern_measure_item:
+			a_expr AS ColLabel
+				{
+					$$ = makeNode(ResTarget);
+					$$->name = $3;
+					$$->indirection = NIL;
+					$$->val = (Node *) $1;
+					$$->location = @1;
+				}
+		;
+
 /*
  * For frame clauses, we return a WindowDef, but only some fields are used:
  * frameOptions, startOffset, and endOffset.
@@ -16527,6 +16571,143 @@ opt_window_exclusion_clause:
 			| /*EMPTY*/				{ $$ = 0; }
 		;
 
+opt_row_pattern_common_syntax:
+opt_row_pattern_skip_to opt_row_pattern_initial_or_seek
+				PATTERN_P '(' row_pattern ')'
+				opt_row_pattern_subset_clause
+				DEFINE row_pattern_definition_list
+			{
+				RPCommonSyntax *n = makeNode(RPCommonSyntax);
+				n->rpSkipTo = ((RPCommonSyntax *)$1)->rpSkipTo;
+				n->rpSkipVariable = ((RPCommonSyntax *)$1)->rpSkipVariable;
+				n->initial = $2;
+				n->rpPatterns = $5;
+				n->rpSubsetClause = $7;
+				n->rpDefs = $9;
+				$$ = (Node *) n;
+			}
+			| /*EMPTY*/		{ $$ = NULL; }
+	;
+
+opt_row_pattern_skip_to:
+			AFTER MATCH SKIP TO NEXT ROW
+				{
+					RPCommonSyntax *n = makeNode(RPCommonSyntax);
+					n->rpSkipTo = ST_NEXT_ROW;
+					n->rpSkipVariable = NULL;
+					$$ = (Node *) n;
+			}
+			| AFTER MATCH SKIP PAST LAST_P ROW
+				{
+					RPCommonSyntax *n = makeNode(RPCommonSyntax);
+					n->rpSkipTo = ST_PAST_LAST_ROW;
+					n->rpSkipVariable = NULL;
+					$$ = (Node *) n;
+				}
+			| AFTER MATCH SKIP TO first_or_last ColId
+				{
+					RPCommonSyntax *n = makeNode(RPCommonSyntax);
+					n->rpSkipTo = $5? ST_FIRST_VARIABLE : ST_LAST_VARIABLE;
+					n->rpSkipVariable = $6;
+					$$ = (Node *) n;
+				}
+/*
+			| AFTER MATCH SKIP TO LAST_P ColId		%prec LAST_P
+				{
+					RPCommonSyntax *n = makeNode(RPCommonSyntax);
+					n->rpSkipTo = ST_LAST_VARIABLE;
+					n->rpSkipVariable = $6;
+					$$ = n;
+				}
+			| AFTER MATCH SKIP TO ColId
+				{
+					RPCommonSyntax *n = makeNode(RPCommonSyntax);
+					n->rpSkipTo = ST_VARIABLE;
+					n->rpSkipVariable = $5;
+					$$ = n;
+				}
+*/
+			| /*EMPTY*/
+				{
+					RPCommonSyntax *n = makeNode(RPCommonSyntax);
+					/* temporary set default to ST_NEXT_ROW */
+					n->rpSkipTo = ST_PAST_LAST_ROW;
+					n->rpSkipVariable = NULL;
+					$$ = (Node *) n;
+				}
+	;
+
+first_or_last:
+			FIRST_P		{ $$ = true; }
+			| LAST_P	{ $$ = false; }
+	;
+
+opt_row_pattern_initial_or_seek:
+			INITIAL			{ $$ = true; }
+			| SEEK
+				{
+					ereport(ERROR,
+							(errcode(ERRCODE_SYNTAX_ERROR),
+							 errmsg("SEEK is not supported"),
+							 errhint("Use INITIAL."),
+							 parser_errposition(@1)));
+				}
+			| /*EMPTY*/		{ $$ = true; }
+		;
+
+row_pattern:
+			row_pattern_term							{ $$ = list_make1($1); }
+			| row_pattern row_pattern_term				{ $$ = lappend($1, $2); }
+		;
+
+row_pattern_term:
+			ColId	{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "", (Node *)makeString($1), NULL, @1); }
+			| ColId '*'	{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "*", (Node *)makeString($1), NULL, @1); }
+			| ColId '+'	{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "+", (Node *)makeString($1), NULL, @1); }
+			| ColId '?'	{ $$ = (Node *) makeSimpleA_Expr(AEXPR_OP, "?", (Node *)makeString($1), NULL, @1); }
+		;
+
+opt_row_pattern_subset_clause:
+			SUBSET row_pattern_subset_list	{ $$ = $2; }
+			| /*EMPTY*/												{ $$ = NIL; }
+		;
+
+row_pattern_subset_list:
+			row_pattern_subset_item									{ $$ = list_make1($1); }
+			| row_pattern_subset_list ',' row_pattern_subset_item	{ $$ = lappend($1, $3); }
+			| /*EMPTY*/												{ $$ = NIL; }
+		;
+
+row_pattern_subset_item: ColId '=' '(' row_pattern_subset_rhs ')'
+			{
+				RPSubsetItem *n = makeNode(RPSubsetItem);
+				n->name = $1;
+				n->rhsVariable = $4;
+				$$ = (Node *) n;
+			}
+		;
+
+row_pattern_subset_rhs:
+			ColId								{ $$ = list_make1(makeStringConst($1, @1)); }
+			| row_pattern_subset_rhs ',' ColId	{ $$ = lappend($1, makeStringConst($3, @1)); }
+			| /*EMPTY*/							{ $$ = NIL; }
+		;
+
+row_pattern_definition_list:
+			row_pattern_definition										{ $$ = list_make1($1); }
+			| row_pattern_definition_list ',' row_pattern_definition	{ $$ = lappend($1, $3); }
+		;
+
+row_pattern_definition:
+			ColId AS a_expr
+				{
+					$$ = makeNode(ResTarget);
+					$$->name = $1;
+					$$->indirection = NIL;
+					$$->val = (Node *) $3;
+					$$->location = @1;
+				}
+		;
 
 /*
  * Supporting nonterminals for expressions.
@@ -17737,6 +17918,7 @@ unreserved_keyword:
 			| INDEXES
 			| INHERIT
 			| INHERITS
+			| INITIAL
 			| INLINE_P
 			| INPUT_P
 			| INSENSITIVE
@@ -17765,6 +17947,7 @@ unreserved_keyword:
 			| MATCHED
 			| MATERIALIZED
 			| MAXVALUE
+			| MEASURES
 			| MERGE
 			| METHOD
 			| MINUTE_P
@@ -17810,8 +17993,11 @@ unreserved_keyword:
 			| PARTITIONS
 			| PASSING
 			| PASSWORD
+			| PAST
 			| PATH
+			| PATTERN_P
 			| PERIOD
+			| PERMUTE
 			| PLAN
 			| PLANS
 			| POLICY
@@ -17864,6 +18050,7 @@ unreserved_keyword:
 			| SEARCH
 			| SECOND_P
 			| SECURITY
+			| SEEK
 			| SEQUENCE
 			| SEQUENCES
 			| SERIALIZABLE
@@ -17892,6 +18079,7 @@ unreserved_keyword:
 			| STRING_P
 			| STRIP_P
 			| SUBSCRIPTION
+			| SUBSET
 			| SUPPORT
 			| SYSID
 			| SYSTEM_P
@@ -18086,6 +18274,7 @@ reserved_keyword:
 			| CURRENT_USER
 			| DEFAULT
 			| DEFERRABLE
+			| DEFINE
 			| DESC
 			| DISTINCT
 			| DO
@@ -18249,6 +18438,7 @@ bare_label_keyword:
 			| DEFAULTS
 			| DEFERRABLE
 			| DEFERRED
+			| DEFINE
 			| DEFINER
 			| DELETE_P
 			| DELIMITER
@@ -18326,6 +18516,7 @@ bare_label_keyword:
 			| INDEXES
 			| INHERIT
 			| INHERITS
+			| INITIAL
 			| INITIALLY
 			| INLINE_P
 			| INNER_P
@@ -18380,6 +18571,7 @@ bare_label_keyword:
 			| MATCHED
 			| MATERIALIZED
 			| MAXVALUE
+			| MEASURES
 			| MERGE
 			| MERGE_ACTION
 			| METHOD
@@ -18437,8 +18629,11 @@ bare_label_keyword:
 			| PARTITIONS
 			| PASSING
 			| PASSWORD
+			| PAST
 			| PATH
+			| PATTERN_P
 			| PERIOD
+			| PERMUTE
 			| PLACING
 			| PLAN
 			| PLANS
@@ -18497,6 +18692,7 @@ bare_label_keyword:
 			| SCROLL
 			| SEARCH
 			| SECURITY
+			| SEEK
 			| SELECT
 			| SEQUENCE
 			| SEQUENCES
@@ -18531,6 +18727,7 @@ bare_label_keyword:
 			| STRING_P
 			| STRIP_P
 			| SUBSCRIPTION
+			| SUBSET
 			| SUBSTRING
 			| SUPPORT
 			| SYMMETRIC
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 3ca06fc3af..9e65e9132c 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -550,6 +550,48 @@ typedef struct SortBy
 	ParseLoc	location;		/* operator location, or -1 if none/unknown */
 } SortBy;
 
+/*
+ * AFTER MATCH row pattern skip to types in row pattern common syntax
+ */
+typedef enum RPSkipTo
+{
+	ST_NONE,					/* AFTER MATCH omitted */
+	ST_NEXT_ROW,				/* SKIP TO NEXT ROW */
+	ST_PAST_LAST_ROW,			/* SKIP TO PAST LAST ROW */
+	ST_FIRST_VARIABLE,			/* SKIP TO FIRST variable name */
+	ST_LAST_VARIABLE,			/* SKIP TO LAST variable name */
+	ST_VARIABLE					/* SKIP TO variable name */
+}			RPSkipTo;
+
+/*
+ * Row Pattern SUBSET clause item
+ */
+typedef struct RPSubsetItem
+{
+	NodeTag		type;
+	char	   *name;			/* Row Pattern SUBSET clause variable name */
+	List	   *rhsVariable;	/* Row Pattern SUBSET rhs variables (list of
+								 * char *string) */
+}			RPSubsetItem;
+
+/*
+ * RowPatternCommonSyntax - raw representation of row pattern common syntax
+ *
+ */
+typedef struct RPCommonSyntax
+{
+	NodeTag		type;
+	RPSkipTo	rpSkipTo;		/* Row Pattern AFTER MATCH SKIP type */
+	char	   *rpSkipVariable; /* Row Pattern Skip To variable name, if any */
+	bool		initial;		/* true if <row pattern initial or seek> is
+								 * initial */
+	List	   *rpPatterns;		/* PATTERN variables (list of A_Expr) */
+	List	   *rpSubsetClause; /* row pattern subset clause (list of
+								 * RPSubsetItem), if any */
+	List	   *rpDefs;			/* row pattern definitions clause (list of
+								 * ResTarget) */
+}			RPCommonSyntax;
+
 /*
  * WindowDef - raw representation of WINDOW and OVER clauses
  *
@@ -565,6 +607,9 @@ typedef struct WindowDef
 	char	   *refname;		/* referenced window name, if any */
 	List	   *partitionClause;	/* PARTITION BY expression list */
 	List	   *orderClause;	/* ORDER BY (list of SortBy) */
+	List	   *rowPatternMeasures; /* row pattern measures (list of
+									 * ResTarget) */
+	RPCommonSyntax *rpCommonSyntax; /* row pattern common syntax */
 	int			frameOptions;	/* frame_clause options, see below */
 	Node	   *startOffset;	/* expression for starting bound, if any */
 	Node	   *endOffset;		/* expression for ending bound, if any */
@@ -1533,6 +1578,11 @@ typedef struct GroupingSet
  * the orderClause might or might not be copied (see copiedOrder); the framing
  * options are never copied, per spec.
  *
+ * "defineClause" is Row Pattern Recognition DEFINE clause (list of
+ * TargetEntry). TargetEntry.resname represents row pattern definition
+ * variable name. "patternVariable" and "patternRegexp" represents PATTERN
+ * clause.
+ *
  * The information relevant for the query jumbling is the partition clause
  * type and its bounds.
  */
@@ -1562,6 +1612,23 @@ typedef struct WindowClause
 	Index		winref;			/* ID referenced by window functions */
 	/* did we copy orderClause from refname? */
 	bool		copiedOrder pg_node_attr(query_jumble_ignore);
+	/* Row Pattern AFTER MACH SKIP clause */
+	RPSkipTo	rpSkipTo;		/* Row Pattern Skip To type */
+	char	   *rpSkipVariable; /* Row Pattern Skip To variable */
+	bool		initial;		/* true if <row pattern initial or seek> is
+								 * initial */
+	/* Row Pattern DEFINE clause (list of TargetEntry) */
+	List	   *defineClause;
+	/* Row Pattern DEFINE variable initial names (list of String) */
+	List	   *defineInitial;
+	/* Row Pattern PATTERN variable name (list of String) */
+	List	   *patternVariable;
+
+	/*
+	 * Row Pattern PATTERN regular expression quantifier ('+' or ''. list of
+	 * String)
+	 */
+	List	   *patternRegexp;
 } WindowClause;
 
 /*
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index f9a4afd472..df49492629 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -129,6 +129,7 @@ PG_KEYWORD("default", DEFAULT, RESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("defaults", DEFAULTS, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("deferrable", DEFERRABLE, RESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("deferred", DEFERRED, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("define", DEFINE, RESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("definer", DEFINER, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("delete", DELETE_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("delimiter", DELIMITER, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -215,6 +216,7 @@ PG_KEYWORD("index", INDEX, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("indexes", INDEXES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("inherit", INHERIT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("inherits", INHERITS, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("initial", INITIAL, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("initially", INITIALLY, RESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("inline", INLINE_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("inner", INNER_P, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
@@ -273,6 +275,7 @@ PG_KEYWORD("match", MATCH, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("matched", MATCHED, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("materialized", MATERIALIZED, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("maxvalue", MAXVALUE, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("measures", MEASURES, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("merge", MERGE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("merge_action", MERGE_ACTION, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("method", METHOD, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -338,8 +341,11 @@ PG_KEYWORD("partition", PARTITION, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("partitions", PARTITIONS, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("passing", PASSING, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("password", PASSWORD, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("past", PAST, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("path", PATH, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("pattern", PATTERN_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("period", PERIOD, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("permute", PERMUTE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("placing", PLACING, RESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("plan", PLAN, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("plans", PLANS, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -401,6 +407,7 @@ PG_KEYWORD("scroll", SCROLL, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("search", SEARCH, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("second", SECOND_P, UNRESERVED_KEYWORD, AS_LABEL)
 PG_KEYWORD("security", SECURITY, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("seek", SEEK, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("select", SELECT, RESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sequence", SEQUENCE, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("sequences", SEQUENCES, UNRESERVED_KEYWORD, BARE_LABEL)
@@ -435,6 +442,7 @@ PG_KEYWORD("strict", STRICT_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("string", STRING_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("strip", STRIP_P, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("subscription", SUBSCRIPTION, UNRESERVED_KEYWORD, BARE_LABEL)
+PG_KEYWORD("subset", SUBSET, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("substring", SUBSTRING, COL_NAME_KEYWORD, BARE_LABEL)
 PG_KEYWORD("support", SUPPORT, UNRESERVED_KEYWORD, BARE_LABEL)
 PG_KEYWORD("symmetric", SYMMETRIC, RESERVED_KEYWORD, BARE_LABEL)
diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index 5b781d87a9..66935afff8 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -51,6 +51,7 @@ typedef enum ParseExprKind
 	EXPR_KIND_WINDOW_FRAME_RANGE,	/* window frame clause with RANGE */
 	EXPR_KIND_WINDOW_FRAME_ROWS,	/* window frame clause with ROWS */
 	EXPR_KIND_WINDOW_FRAME_GROUPS,	/* window frame clause with GROUPS */
+	EXPR_KIND_RPR_DEFINE,		/* DEFINE */
 	EXPR_KIND_SELECT_TARGET,	/* SELECT target list item */
 	EXPR_KIND_INSERT_TARGET,	/* INSERT target list item */
 	EXPR_KIND_UPDATE_SOURCE,	/* UPDATE assignment source item */
-- 
2.25.1


----Next_Part(Sat_May_11_16_23_07_2024_789)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="v18-0002-Row-pattern-recognition-patch-parse-analysis.patch"



^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread

* [PATCH v49 7/7] WIP add max_repack_replication_slots
@ 2026-04-01 17:54  Álvaro Herrera <alvherre@kurilemu.de>
  0 siblings, 0 replies; 452+ messages in thread

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

---
 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                | 77 +++++++++++--------
 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 +-
 9 files changed, 74 insertions(+), 42 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 106b2b60441..00b21ede481 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -228,8 +228,8 @@ 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 a9092fc2382..fe6bfeba25e 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 1;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -190,12 +193,14 @@ 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;
 }
@@ -208,7 +213,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +227,7 @@ 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];
 
@@ -372,6 +377,7 @@ 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 +385,11 @@ 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 +438,16 @@ 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];
 
@@ -444,7 +455,9 @@ 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);
@@ -547,7 +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 < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +588,7 @@ 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;
 }
@@ -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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 < TotalMaxReplicationSlots; 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 (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;
@@ -1453,11 +1466,11 @@ 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;
 
@@ -1514,13 +1527,13 @@ 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;
@@ -1617,11 +1630,11 @@ 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;
@@ -1662,7 +1675,10 @@ 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")));
@@ -2216,7 +2232,7 @@ 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);
@@ -2224,7 +2240,7 @@ 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;
@@ -2329,7 +2345,7 @@ 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];
@@ -2430,7 +2446,7 @@ 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 */
@@ -2860,7 +2876,7 @@ 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;
 
@@ -2902,6 +2918,7 @@ 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 fbbe09135bf..caea3ed1257 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 0a862693fcd..d12a3bd7bdf 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 => '1',
+  min => '0',
+  max => 'MAX_BACKENDS /* XXX? */',
+},
+
 /* 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 cf15597385b..15014f37753 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 = 1 # 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


--3n3vqr5y2jhknrqj--





^ permalink  raw  reply  [nested|flat] 452+ messages in thread