Fix assertion failures while processing NEW_CID record in logical decoding.

When the logical decoding restarts from NEW_CID, since there is no
association between the top transaction and its subtransaction, both are
created as top transactions and have the same LSN. This caused the
assertion failure in AssertTXNLsnOrder().

This patch skips the assertion check until we reach the LSN at which we
start decoding the contents of the transaction, specifically
start_decoding_at LSN in SnapBuild. This is okay because we don't
guarantee to make the association between top transaction and
subtransaction until we try to decode the actual contents of transaction.
The ordering of the records prior to the start_decoding_at LSN should have
been checked before the restart.

The other assertion failure is due to the reason that we forgot to track
that we have considered top-level transaction id in the list of catalog
changing transactions that were committed when one of its subtransactions
is marked as containing catalog change.

Reported-by: Tomas Vondra, Osumi Takamichi
Author: Masahiko Sawada, Kuroda Hayato
Reviewed-by: Amit Kapila, Dilip Kumar, Kuroda Hayato, Kyotaro Horiguchi, Masahiko Sawada
Backpatch-through: 10
Discussion: https://postgr.es/m/a89b46b6-0239-2fd5-71a9-b19b1f7a7145%40enterprisedb.com
Discussion: https://postgr.es/m/TYCPR01MB83733C6CEAE47D0280814D5AED7A9%40TYCPR01MB8373.jpnprd01.prod.outlook.com

2 files changed, 17 insertions, 0 deletions

diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 368f60159da..967e5227423 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -722,10 +722,24 @@ static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
 #ifdef USE_ASSERT_CHECKING
+	LogicalDecodingContext *ctx = rb->private_data;
 	dlist_iter	iter;
 	XLogRecPtr	prev_first_lsn = InvalidXLogRecPtr;
 	XLogRecPtr	prev_base_snap_lsn = InvalidXLogRecPtr;
 
+	/*
+	 * Skip the verification if we don't reach the LSN at which we start
+	 * decoding the contents of transactions yet because until we reach the
+	 * LSN, we could have transactions that don't have the association between
+	 * the top-level transaction and subtransaction yet and consequently have
+	 * the same LSN.  We don't guarantee this association until we try to
+	 * decode the actual contents of transaction. The ordering of the records
+	 * prior to the start_decoding_at LSN should have been checked before the
+	 * restart.
+	 */
+	if (SnapBuildXactNeedsSkip(ctx->snapshot_builder, ctx->reader->EndRecPtr))
+		return;
+
 	dlist_foreach(iter, &rb->toplevel_by_lsn)
 	{
 		ReorderBufferTXN *cur_txn = dlist_container(ReorderBufferTXN, node,
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index d407fb3440e..1e7c918bdeb 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1103,6 +1103,9 @@ SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid,
 	else if (sub_needs_timetravel)
 	{
 		/* track toplevel txn as well, subxact alone isn't meaningful */
+		elog(DEBUG2, "forced transaction %u to do timetravel due to one of its subtransactions",
+			 xid);
+		needs_timetravel = true;
 		SnapBuildAddCommittedTxn(builder, xid);
 	}
 	else if (needs_timetravel)