Subject: [PATCH v5 2/3] Do not use RelationNeedsWAL to identify relation persistence

From: Kyotaro Horiguchi <[email-masked]>
Date: Mon, 18 Jan 2021 14:47:21 +0900

RelationNeedsWAL() may return false for a permanent relation when
wal_level=minimal and the relation is created or truncated in the
current transaction. Directly examine relpersistence instead of using
the function to know relation persistence.
---
 src/backend/catalog/pg_publication.c | 2 +-
 src/backend/optimizer/util/plancat.c | 3 ++-
 src/include/storage/bufmgr.h         | 8 +++++++-
 src/include/utils/rel.h              | 2 +-
 src/include/utils/snapmgr.h          | 2 +-
 5 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/src/backend/catalog/pg_publication.c b/src/backend/catalog/pg_publication.c
index 5f8e1c64e1..84d2efcfd2 100644
--- a/src/backend/catalog/pg_publication.c
+++ b/src/backend/catalog/pg_publication.c
@@ -67,7 +67,7 @@ check_publication_add_relation(Relation targetrel)
 				 errdetail("System tables cannot be added to publications.")));
 
 	/* UNLOGGED and TEMP relations cannot be part of publication. */
-	if (!RelationNeedsWAL(targetrel))
+	if (targetrel->rd_rel->relpersistence != RELPERSISTENCE_PERMANENT)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("table \"%s\" cannot be replicated",
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index da322b453e..177e6e336a 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -126,7 +126,8 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 	relation = table_open(relationObjectId, NoLock);
 
 	/* Temporary and unlogged relations are inaccessible during recovery. */
-	if (!RelationNeedsWAL(relation) && RecoveryInProgress())
+	if (relation->rd_rel->relpersistence != RELPERSISTENCE_PERMANENT &&
+		RecoveryInProgress())
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("cannot access temporary or unlogged relations during recovery")));
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index fb00fda6a7..e641174798 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -14,6 +14,7 @@
 #ifndef BUFMGR_H
 #define BUFMGR_H
 
+#include "access/xlog.h"
 #include "storage/block.h"
 #include "storage/buf.h"
 #include "storage/bufpage.h"
@@ -278,12 +279,17 @@ TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page)
 {
 	Assert(relation != NULL);
 
+	/*
+	 * While wal_level=minimal, early pruning can happen without updating page
+	 * LSN. Don't take the fast-return path while wal_level=minimal so that we
+	 * don't miss early pruning.
+	 */
 	if (old_snapshot_threshold >= 0
 		&& (snapshot) != NULL
 		&& ((snapshot)->snapshot_type == SNAPSHOT_MVCC
 			|| (snapshot)->snapshot_type == SNAPSHOT_TOAST)
 		&& !XLogRecPtrIsInvalid((snapshot)->lsn)
-		&& PageGetLSN(page) > (snapshot)->lsn)
+		&& (!XLogIsNeeded() || PageGetLSN(page) > (snapshot)->lsn))
 		TestForOldSnapshot_impl(snapshot, relation);
 }
 
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index 10b63982c0..f58d65cf28 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -554,7 +554,7 @@ typedef struct ViewOptions
 
 /*
  * RelationNeedsWAL
- *		True if relation needs WAL.
+ *		True if relation needs WAL at the time.
  *
  * Returns false if wal_level = minimal and this relation is created or
  * truncated in the current transaction.  See "Skipping WAL for New
diff --git a/src/include/utils/snapmgr.h b/src/include/utils/snapmgr.h
index 579be352c5..c21ee3c289 100644
--- a/src/include/utils/snapmgr.h
+++ b/src/include/utils/snapmgr.h
@@ -37,7 +37,7 @@
  */
 #define RelationAllowsEarlyPruning(rel) \
 ( \
-	 RelationNeedsWAL(rel) \
+	 (rel)->rd_rel->relpersistence == RELPERSISTENCE_PERMANENT	\
   && !IsCatalogRelation(rel) \
   && !RelationIsAccessibleInLogicalDecoding(rel) \
 )
-- 
2.27.0

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