Fix catalog lookup with the wrong snapshot during logical decoding.

Previously, we relied on HEAP2_NEW_CID records and XACT_INVALIDATION
records to know if the transaction has modified the catalog, and that
information is not serialized to snapshot. Therefore, after the restart,
if the logical decoding decodes only the commit record of the transaction
that has actually modified a catalog, we will miss adding its XID to the
snapshot. Thus, we will end up looking at catalogs with the wrong
snapshot.

To fix this problem, this change adds the list of transaction IDs and
sub-transaction IDs, that have modified catalogs and are running during
snapshot serialization, to the serialized snapshot. After restart or
otherwise, when we restore from such a serialized snapshot, the
corresponding list is restored in memory. Now, when decoding a COMMIT
record, we check both the list and the ReorderBuffer to see if the
transaction has modified catalogs.

Since this adds additional information to the serialized snapshot, we
cannot backpatch it. For back branches, we took another approach.
We remember the last-running-xacts list of the decoded RUNNING_XACTS
record after restoring the previously serialized snapshot. Then, we mark
the transaction as containing catalog changes if it's in the list of
initial running transactions and its commit record has
XACT_XINFO_HAS_INVALS. This doesn't require any file format changes but
the transaction will end up being added to the snapshot even if it has
only relcache invalidations. But that won't be a problem since we use
snapshot built during decoding only to read system catalogs.

This commit bumps SNAPBUILD_VERSION because of a change in SnapBuild.

Reported-by: Mike Oh
Author: Masahiko Sawada
Reviewed-by: Amit Kapila, Shi yu, Takamichi Osumi, Kyotaro Horiguchi, Bertrand Drouvot, Ahsan Hadi
Backpatch-through: 10
Discussion: https://postgr.es/m/81D0D8B0-E7C4-4999-B616-1E5004DBDCD2%40amazon.com

2 files changed, 13 insertions, 1 deletions

diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 2c9206ace41..8695901ba71 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -381,6 +381,11 @@ typedef struct ReorderBufferTXN
 	dlist_node	node;
 
 	/*
+	 * A node in the list of catalog modifying transactions
+	 */
+	dlist_node	catchange_node;
+
+	/*
 	 * Size of this transaction (changes currently in memory, in bytes).
 	 */
 	Size		size;
@@ -527,6 +532,12 @@ struct ReorderBuffer
 	dlist_head	txns_by_base_snapshot_lsn;
 
 	/*
+	 * Transactions and subtransactions that have modified system catalogs.
+	 */
+	dlist_head	catchange_txns;
+	int			catchange_ntxns;
+
+	/*
 	 * one-entry sized cache for by_txn. Very frequently the same txn gets
 	 * looked up over and over again.
 	 */
@@ -677,6 +688,7 @@ extern void ReorderBufferSkipPrepare(ReorderBuffer *rb, TransactionId xid);
 extern void ReorderBufferPrepare(ReorderBuffer *rb, TransactionId xid, char *gid);
 extern ReorderBufferTXN *ReorderBufferGetOldestTXN(ReorderBuffer *);
 extern TransactionId ReorderBufferGetOldestXmin(ReorderBuffer *rb);
+extern TransactionId *ReorderBufferGetCatalogChangesXacts(ReorderBuffer *rb);
 
 extern void ReorderBufferSetRestartPoint(ReorderBuffer *, XLogRecPtr ptr);
 
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index d179251aad9..e6adea24f22 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -82,7 +82,7 @@ extern void SnapBuildSetTwoPhaseAt(SnapBuild *builder, XLogRecPtr ptr);
 
 extern void SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn,
 							   TransactionId xid, int nsubxacts,
-							   TransactionId *subxacts);
+							   TransactionId *subxacts, uint32 xinfo);
 extern bool SnapBuildProcessChange(SnapBuild *builder, TransactionId xid,
 								   XLogRecPtr lsn);
 extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,