WAL Log invalidations at command end with wal_level=logical.

When wal_level=logical, write invalidations at command end into WAL so
that decoding can use this information.

This patch is required to allow the streaming of in-progress transactions
in logical decoding.  The actual work to allow streaming will be committed
as a separate patch.

We still add the invalidations to the cache and write them to WAL at
commit time in RecordTransactionCommit(). This uses the existing
XLOG_INVALIDATIONS xlog record type, from the RM_STANDBY_ID resource
manager (see LogStandbyInvalidations for details).

So existing code relying on those invalidations (e.g. redo) does not need
to be changed.

The invalidations written at command end uses a new xlog record type
XLOG_XACT_INVALIDATIONS, from RM_XACT_ID resource manager. See
LogLogicalInvalidations for details.

These new xlog records are ignored by existing redo procedures, which
still rely on the invalidations written to commit records.

The invalidations are decoded and accumulated in top-transaction, and then
executed during replay.  This obviates the need to decode the
invalidations as part of a commit record.

Bump XLOG_PAGE_MAGIC, since this introduces XLOG_XACT_INVALIDATIONS.

Author: Dilip Kumar, Tomas Vondra, Amit Kapila
Reviewed-by: Amit Kapila
Tested-by: Neha Sharma and Mahendra Singh Thalor
Discussion: https://postgr.es/m/688b0b7f-2f6c-d827-c27b-216a8e3ea700@2ndquadrant.com

1 files changed, 54 insertions, 0 deletions

diff --git a/src/backend/utils/cache/inval.c b/src/backend/utils/cache/inval.c
index 591dd33be67..628d6f5d0cc 100644
--- a/src/backend/utils/cache/inval.c
+++ b/src/backend/utils/cache/inval.c
@@ -85,6 +85,9 @@
  *	worth trying to avoid sending such inval traffic in the future, if those
  *	problems can be overcome cheaply.
  *
+ *	When wal_level=logical, write invalidations into WAL at each command end to
+ *	support the decoding of the in-progress transactions.  See
+ *	CommandEndInvalidationMessages.
  *
  * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -1094,6 +1097,11 @@ CommandEndInvalidationMessages(void)
 
 	ProcessInvalidationMessages(&transInvalInfo->CurrentCmdInvalidMsgs,
 								LocalExecuteInvalidationMessage);
+
+	/* WAL Log per-command invalidation messages for wal_level=logical */
+	if (XLogLogicalInfoActive())
+		LogLogicalInvalidations();
+
 	AppendInvalidationMessages(&transInvalInfo->PriorCmdInvalidMsgs,
 							   &transInvalInfo->CurrentCmdInvalidMsgs);
 }
@@ -1501,3 +1509,49 @@ CallSyscacheCallbacks(int cacheid, uint32 hashvalue)
 		i = ccitem->link - 1;
 	}
 }
+
+/*
+ * LogLogicalInvalidations
+ *
+ * Emit WAL for invalidations.  This is currently only used for logging
+ * invalidations at the command end or at commit time if any invalidations
+ * are pending.
+ */
+void
+LogLogicalInvalidations()
+{
+	xl_xact_invals xlrec;
+	SharedInvalidationMessage *invalMessages;
+	int			nmsgs = 0;
+
+	/* Quick exit if we haven't done anything with invalidation messages. */
+	if (transInvalInfo == NULL)
+		return;
+
+	ProcessInvalidationMessagesMulti(&transInvalInfo->CurrentCmdInvalidMsgs,
+									 MakeSharedInvalidMessagesArray);
+
+	Assert(!(numSharedInvalidMessagesArray > 0 &&
+			 SharedInvalidMessagesArray == NULL));
+
+	invalMessages = SharedInvalidMessagesArray;
+	nmsgs = numSharedInvalidMessagesArray;
+	SharedInvalidMessagesArray = NULL;
+	numSharedInvalidMessagesArray = 0;
+
+	if (nmsgs > 0)
+	{
+		/* prepare record */
+		memset(&xlrec, 0, MinSizeOfXactInvals);
+		xlrec.nmsgs = nmsgs;
+
+		/* perform insertion */
+		XLogBeginInsert();
+		XLogRegisterData((char *) (&xlrec), MinSizeOfXactInvals);
+		XLogRegisterData((char *) invalMessages,
+						 nmsgs * sizeof(SharedInvalidationMessage));
+		XLogInsert(RM_XACT_ID, XLOG_XACT_INVALIDATIONS);
+
+		pfree(invalMessages);
+	}
+}