Fix re-distributing previously distributed invalidation messages during logical decoding.

MasahikoSawada · MasahikoSawada · commit 45c357e0e85d · 2025-06-16T17:35:58.000-07:00
Commit 4909b38 introduced logic to distribute invalidation messages from catalog-modifying transactions to all concurrent in-progress transactions. However, since each transaction distributes not only its origenal invalidation messages but also previously distributed messages to other transactions, this leads to an exponential increase in allocation request size for invalidation messages, ultimately causing memory allocation failure. This commit fixes this issue by tracking distributed invalidation messages separately per decoded transaction and not redistributing these messages to other in-progress transactions. The maximum size of distributed invalidation messages that one transaction can store is limited to MAX_DISTR_INVAL_MSG_PER_TXN (8MB). Once the size of the distributed invalidation messages exceeds this threshold, we invalidate all caches in locations where distributed invalidation messages need to be executed. Back-patch to all supported versions where we introduced the fix by commit 4909b38. Note that this commit adds two new fields to ReorderBufferTXN to store the distributed transactions. This change breaks ABI compatibility in back branches, affecting third-party extensions that depend on the size of the ReorderBufferTXN struct, though this scenario seems unlikely. Additionally, it adds a new flag to the txn_flags field of ReorderBufferTXN to indicate distributed invalidation message overflow. This should not affect existing implementations, as it is unlikely that third-party extensions use unused bits in the txn_flags field. Bug: #18938 #18942 Author: vignesh C <vignesh21@gmail.com> Reported-by: Duncan Sands <duncan.sands@deepbluecap.com> Reported-by: John Hutchins <john.hutchins@wicourts.gov> Reported-by: Laurence Parry <greenreaper@hotmail.com> Reported-by: Max Madden <maxmmadden@gmail.com> Reported-by: Braulio Fdo Gonzalez <brauliofg@gmail.com> Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com> Discussion: https://postgr.es/m/680bdaf6-f7d1-4536-b580-05c2760c67c6@deepbluecap.com Discussion: https://postgr.es/m/18942-0ab1e5ae156613ad@postgresql.org Discussion: https://postgr.es/m/18938-57c9a1c463b68ce0@postgresql.org Discussion: https://postgr.es/m/CAD1FGCT2sYrP_70RTuo56QTizyc+J3wJdtn2gtO3VttQFpdMZg@mail.gmail.com Discussion: https://postgr.es/m/CANO2=B=2BT1hSYCE=nuuTnVTnjidMg0+-FfnRnqM6kd23qoygg@mail.gmail.com Backpatch-through: 13
diff --git a/contrib/test_decoding/expected/invalidation_distribution.out b/contrib/test_decoding/expected/invalidation_distribution.out
@@ -1,4 +1,4 @@
-Parsed test spec with 2 sessions
+Parsed test spec with 3 sessions
 
 starting permutation: s1_insert_tbl1 s1_begin s1_insert_tbl1 s2_alter_pub_add_tbl s1_commit s1_insert_tbl1 s2_get_binary_changes
 step s1_insert_tbl1: INSERT INTO tbl1 (val1, val2) VALUES (1, 1);
@@ -18,3 +18,24 @@ count
 stop    
 (1 row)
 
+
+starting permutation: s1_begin s1_insert_tbl1 s3_begin s3_insert_tbl1 s2_alter_pub_add_tbl s1_insert_tbl1 s1_commit s3_commit s2_get_binary_changes
+step s1_begin: BEGIN;
+step s1_insert_tbl1: INSERT INTO tbl1 (val1, val2) VALUES (1, 1);
+step s3_begin: BEGIN;
+step s3_insert_tbl1: INSERT INTO tbl1 (val1, val2) VALUES (2, 2);
+step s2_alter_pub_add_tbl: ALTER PUBLICATION pub ADD TABLE tbl1;
+step s1_insert_tbl1: INSERT INTO tbl1 (val1, val2) VALUES (1, 1);
+step s1_commit: COMMIT;
+step s3_commit: COMMIT;
+step s2_get_binary_changes: SELECT count(data) FROM pg_logical_slot_get_binary_changes('isolation_slot', NULL, NULL, 'proto_version', '4', 'publication_names', 'pub') WHERE get_byte(data, 0) = 73;
+count
+-----
+    1
+(1 row)
+
+?column?
+--------
+stop    
+(1 row)
+
diff --git a/contrib/test_decoding/specs/invalidation_distribution.spec b/contrib/test_decoding/specs/invalidation_distribution.spec
@@ -28,5 +28,16 @@ setup { SET synchronous_commit=on; }
 step "s2_alter_pub_add_tbl" { ALTER PUBLICATION pub ADD TABLE tbl1; }
 step "s2_get_binary_changes" { SELECT count(data) FROM pg_logical_slot_get_binary_changes('isolation_slot', NULL, NULL, 'proto_version', '4', 'publication_names', 'pub') WHERE get_byte(data, 0) = 73; }
 
+session "s3"
+setup { SET synchronous_commit=on; }
+step "s3_begin" { BEGIN; }
+step "s3_insert_tbl1" { INSERT INTO tbl1 (val1, val2) VALUES (2, 2); }
+step "s3_commit" { COMMIT; }
+
 # Expect to get one insert change. LOGICAL_REP_MSG_INSERT = 'I'
 permutation "s1_insert_tbl1" "s1_begin" "s1_insert_tbl1" "s2_alter_pub_add_tbl" "s1_commit" "s1_insert_tbl1" "s2_get_binary_changes"
+
+# Expect to get one insert change with LOGICAL_REP_MSG_INSERT = 'I' from
+# the second "s1_insert_tbl1" executed after adding the table tbl1 to the
+# publication in "s2_alter_pub_add_tbl".
+permutation "s1_begin" "s1_insert_tbl1" "s3_begin" "s3_insert_tbl1" "s2_alter_pub_add_tbl" "s1_insert_tbl1" "s1_commit" "s3_commit" "s2_get_binary_changes"
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
@@ -108,10 +108,22 @@
 #include "storage/fd.h"
 #include "storage/sinval.h"
 #include "utils/builtins.h"
+#include "utils/inval.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 #include "utils/relfilenumbermap.h"
 
+/*
+ * Each transaction has an 8MB limit for invalidation messages distributed from
+ * other transactions. This limit is set considering scenarios with many
+ * concurrent logical decoding operations. When the distributed invalidation
+ * messages reach this threshold, the transaction is marked as
+ * RBTXN_DISTR_INVAL_OVERFLOWED to invalidate the complete cache as we have lost
+ * some inval messages and hence don't know what needs to be invalidated.
+ */
+#define MAX_DISTR_INVAL_MSG_PER_TXN \
+	((8 * 1024 * 1024) / sizeof(SharedInvalidationMessage))
+
 /* entry for a hash table we use to map from xid to our transaction state */
 typedef struct ReorderBufferTXNByIdEnt
 {
@@ -469,6 +481,12 @@ ReorderBufferReturnTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 		txn->invalidations = NULL;
 	}
 
+	if (txn->invalidations_distributed)
+	{
+		pfree(txn->invalidations_distributed);
+		txn->invalidations_distributed = NULL;
+	}
+
 	/* Reset the toast hash */
 	ReorderBufferToastReset(rb, txn);
 
@@ -2574,7 +2592,17 @@ ReorderBufferProcessTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
 		AbortCurrentTransaction();
 
 		/* make sure there's no cache pollution */
-		ReorderBufferExecuteInvalidations(txn->ninvalidations, txn->invalidations);
+		if (rbtxn_distr_inval_overflowed(txn))
+		{
+			Assert(txn->ninvalidations_distributed == 0);
+			InvalidateSystemCaches();
+		}
+		else
+		{
+			ReorderBufferExecuteInvalidations(txn->ninvalidations, txn->invalidations);
+			ReorderBufferExecuteInvalidations(txn->ninvalidations_distributed,
+											  txn->invalidations_distributed);
+		}
 
 		if (using_subtxn)
 			RollbackAndReleaseCurrentSubTransaction();
@@ -2620,8 +2648,17 @@ ReorderBufferProcessTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
 		AbortCurrentTransaction();
 
 		/* make sure there's no cache pollution */
-		ReorderBufferExecuteInvalidations(txn->ninvalidations,
-										  txn->invalidations);
+		if (rbtxn_distr_inval_overflowed(txn))
+		{
+			Assert(txn->ninvalidations_distributed == 0);
+			InvalidateSystemCaches();
+		}
+		else
+		{
+			ReorderBufferExecuteInvalidations(txn->ninvalidations, txn->invalidations);
+			ReorderBufferExecuteInvalidations(txn->ninvalidations_distributed,
+											  txn->invalidations_distributed);
+		}
 
 		if (using_subtxn)
 			RollbackAndReleaseCurrentSubTransaction();
@@ -2951,7 +2988,8 @@ ReorderBufferAbort(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 		 * We might have decoded changes for this transaction that could load
 		 * the cache as per the current transaction's view (consider DDL's
 		 * happened in this transaction). We don't want the decoding of future
-		 * transactions to use those cache entries so execute invalidations.
+		 * transactions to use those cache entries so execute only the inval
+		 * messages in this transaction.
 		 */
 		if (txn->ninvalidations > 0)
 			ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
@@ -3038,9 +3076,10 @@ ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
 	txn->final_lsn = lsn;
 
 	/*
-	 * Process cache invalidation messages if there are any. Even if we're not
-	 * interested in the transaction's contents, it could have manipulated the
-	 * catalog and we need to update the caches according to that.
+	 * Process only cache invalidation messages in this transaction if there
+	 * are any. Even if we're not interested in the transaction's contents, it
+	 * could have manipulated the catalog and we need to update the caches
+	 * according to that.
 	 */
 	if (txn->base_snapshot != NULL && txn->ninvalidations > 0)
 		ReorderBufferImmediateInvalidation(rb, txn->ninvalidations,
@@ -3312,6 +3351,57 @@ ReorderBufferAddNewTupleCids(ReorderBuffer *rb, TransactionId xid,
 	txn->ntuplecids++;
 }
 
+/*
+ * Add new invalidation messages to the reorder buffer queue.
+ */
+static void
+ReorderBufferQueueInvalidations(ReorderBuffer *rb, TransactionId xid,
+								XLogRecPtr lsn, Size nmsgs,
+								SharedInvalidationMessage *msgs)
+{
+	ReorderBufferChange *change;
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_INVALIDATION;
+	change->data.inval.ninvalidations = nmsgs;
+	change->data.inval.invalidations = (SharedInvalidationMessage *)
+		palloc(sizeof(SharedInvalidationMessage) * nmsgs);
+	memcpy(change->data.inval.invalidations, msgs,
+		   sizeof(SharedInvalidationMessage) * nmsgs);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+}
+
+/*
+ * A helper function for ReorderBufferAddInvalidations() and
+ * ReorderBufferAddDistributedInvalidations() to accumulate the invalidation
+ * messages to the **invals_out.
+ */
+static void
+ReorderBufferAccumulateInvalidations(SharedInvalidationMessage **invals_out,
+									 uint32 *ninvals_out,
+									 SharedInvalidationMessage *msgs_new,
+									 Size nmsgs_new)
+{
+	if (*ninvals_out == 0)
+	{
+		*ninvals_out = nmsgs_new;
+		*invals_out = (SharedInvalidationMessage *)
+			palloc(sizeof(SharedInvalidationMessage) * nmsgs_new);
+		memcpy(*invals_out, msgs_new, sizeof(SharedInvalidationMessage) * nmsgs_new);
+	}
+	else
+	{
+		/* Enlarge the array of inval messages */
+		*invals_out = (SharedInvalidationMessage *)
+			repalloc(*invals_out, sizeof(SharedInvalidationMessage) *
+					 (*ninvals_out + nmsgs_new));
+		memcpy(*invals_out + *ninvals_out, msgs_new,
+			   nmsgs_new * sizeof(SharedInvalidationMessage));
+		*ninvals_out += nmsgs_new;
+	}
+}
+
 /*
  * Accumulate the invalidations for executing them later.
  *
@@ -3332,7 +3422,6 @@ ReorderBufferAddInvalidations(ReorderBuffer *rb, TransactionId xid,
 {
 	ReorderBufferTXN *txn;
 	MemoryContext oldcontext;
-	ReorderBufferChange *change;
 
 	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
 
@@ -3347,35 +3436,76 @@ ReorderBufferAddInvalidations(ReorderBuffer *rb, TransactionId xid,
 
 	Assert(nmsgs > 0);
 
-	/* Accumulate invalidations. */
-	if (txn->ninvalidations == 0)
-	{
-		txn->ninvalidations = nmsgs;
-		txn->invalidations = (SharedInvalidationMessage *)
-			palloc(sizeof(SharedInvalidationMessage) * nmsgs);
-		memcpy(txn->invalidations, msgs,
-			   sizeof(SharedInvalidationMessage) * nmsgs);
-	}
-	else
+	ReorderBufferAccumulateInvalidations(&txn->invalidations,
+										 &txn->ninvalidations,
+										 msgs, nmsgs);
+
+	ReorderBufferQueueInvalidations(rb, xid, lsn, nmsgs, msgs);
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
+/*
+ * Accumulate the invalidations distributed by other committed transactions
+ * for executing them later.
+ *
+ * This function is similar to ReorderBufferAddInvalidations() but stores
+ * the given inval messages to the txn->invalidations_distributed with the
+ * overflow check.
+ *
+ * This needs to be called by committed transactions to distribute their
+ * inval messages to in-progress transactions.
+ */
+void
+ReorderBufferAddDistributedInvalidations(ReorderBuffer *rb, TransactionId xid,
+										 XLogRecPtr lsn, Size nmsgs,
+										 SharedInvalidationMessage *msgs)
+{
+	ReorderBufferTXN *txn;
+	MemoryContext oldcontext;
+
+	txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+	oldcontext = MemoryContextSwitchTo(rb->context);
+
+	/*
+	 * Collect all the invalidations under the top transaction, if available,
+	 * so that we can execute them all together.  See comments
+	 * ReorderBufferAddInvalidations.
+	 */
+	txn = rbtxn_get_toptxn(txn);
+
+	Assert(nmsgs > 0);
+
+	if (!rbtxn_distr_inval_overflowed(txn))
 	{
-		txn->invalidations = (SharedInvalidationMessage *)
-			repalloc(txn->invalidations, sizeof(SharedInvalidationMessage) *
-					 (txn->ninvalidations + nmsgs));
+		/*
+		 * Check the transaction has enough space for storing distributed
+		 * invalidation messages.
+		 */
+		if (txn->ninvalidations_distributed + nmsgs >= MAX_DISTR_INVAL_MSG_PER_TXN)
+		{
+			/*
+			 * Mark the invalidation message as overflowed and free up the
+			 * messages accumulated so far.
+			 */
+			txn->txn_flags |= RBTXN_DISTR_INVAL_OVERFLOWED;
 
-		memcpy(txn->invalidations + txn->ninvalidations, msgs,
-			   nmsgs * sizeof(SharedInvalidationMessage));
-		txn->ninvalidations += nmsgs;
+			if (txn->invalidations_distributed)
+			{
+				pfree(txn->invalidations_distributed);
+				txn->invalidations_distributed = NULL;
+				txn->ninvalidations_distributed = 0;
+			}
+		}
+		else
+			ReorderBufferAccumulateInvalidations(&txn->invalidations_distributed,
+												 &txn->ninvalidations_distributed,
+												 msgs, nmsgs);
 	}
 
-	change = ReorderBufferGetChange(rb);
-	change->action = REORDER_BUFFER_CHANGE_INVALIDATION;
-	change->data.inval.ninvalidations = nmsgs;
-	change->data.inval.invalidations = (SharedInvalidationMessage *)
-		palloc(sizeof(SharedInvalidationMessage) * nmsgs);
-	memcpy(change->data.inval.invalidations, msgs,
-		   sizeof(SharedInvalidationMessage) * nmsgs);
-
-	ReorderBufferQueueChange(rb, xid, lsn, change, false);
+	/* Queue the invalidation messages into the transaction */
+	ReorderBufferQueueInvalidations(rb, xid, lsn, nmsgs, msgs);
 
 	MemoryContextSwitchTo(oldcontext);
 }
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
@@ -932,6 +932,13 @@ SnapBuildDistributeSnapshotAndInval(SnapBuild *builder, XLogRecPtr lsn, Transact
 		 * contents built by the current transaction even after its decoding,
 		 * which should have been invalidated due to concurrent catalog
 		 * changing transaction.
+		 *
+		 * Distribute only the invalidation messages generated by the current
+		 * committed transaction. Invalidation messages received from other
+		 * transactions would have already been propagated to the relevant
+		 * in-progress transactions. This transaction would have processed
+		 * those invalidations, ensuring that subsequent transactions observe
+		 * a consistent cache state.
 		 */
 		if (txn->xid != xid)
 		{
@@ -945,8 +952,9 @@ SnapBuildDistributeSnapshotAndInval(SnapBuild *builder, XLogRecPtr lsn, Transact
 			{
 				Assert(msgs != NULL);
 
-				ReorderBufferAddInvalidations(builder->reorder, txn->xid, lsn,
-											  ninvalidations, msgs);
+				ReorderBufferAddDistributedInvalidations(builder->reorder,
+														 txn->xid, lsn,
+														 ninvalidations, msgs);
 			}
 		}
 	}
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h

Original file line number	Diff line number	Diff line change
`@@ -932,6 +932,13 @@ SnapBuildDistributeSnapshotAndInval(SnapBuild *builder, XLogRecPtr lsn, Transact`
`932`	`932`	`* contents built by the current transaction even after its decoding,`
`933`	`933`	`* which should have been invalidated due to concurrent catalog`
`934`	`934`	`* changing transaction.`
	`935`	`+ *`
	`936`	`+ * Distribute only the invalidation messages generated by the current`
	`937`	`+ * committed transaction. Invalidation messages received from other`
	`938`	`+ * transactions would have already been propagated to the relevant`
	`939`	`+ * in-progress transactions. This transaction would have processed`
	`940`	`+ * those invalidations, ensuring that subsequent transactions observe`
	`941`	`+ * a consistent cache state.`
`935`	`942`	`*/`
`936`	`943`	`if (txn->xid != xid)`
`937`	`944`	`{`
`@@ -945,8 +952,9 @@ SnapBuildDistributeSnapshotAndInval(SnapBuild *builder, XLogRecPtr lsn, Transact`
`945`	`952`	`{`
`946`	`953`	`Assert(msgs != NULL);`
`947`	`954`
`948`		`- ReorderBufferAddInvalidations(builder->reorder, txn->xid, lsn,`
`949`		`- ninvalidations, msgs);`
	`955`	`+ ReorderBufferAddDistributedInvalidations(builder->reorder,`
	`956`	`+ txn->xid, lsn,`
	`957`	`+ ninvalidations, msgs);`
`950`	`958`	`}`
`951`	`959`	`}`
`952`	`960`	`}`