From 060f9f5ea53752736fa5b3b7bf5779b257265b62 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 17 Jan 2025 13:27:47 +0900
Subject: [PATCH] Revert recent changes related to handling of 2PC files at
 recovery

This commit reverts 8f67f994e8ea (down to v13) and c3de0f9eed38 (down to
v17), as these are proving to not be completely correct regarding two
aspects:
- In v17 and newer branches, c3de0f9eed38's check for epoch handling is
incorrect, and does not correctly handle frozen epochs.  A logic closer
to widen_snapshot_xid() should be used.  The 2PC code should try to
integrate deeper with FullTransactionIds, 5a1dfde8334b being not enough.
- In v13 and newer branches, 8f67f994e8ea is a workaround for the real
issue, which is that we should not attempt CLOG lookups without reaching
consistency.  This exists since 728bd991c3c4, and this is reachable with
ProcessTwoPhaseBuffer() called by restoreTwoPhaseData() at the beginning
of recovery.

Per discussion with Noah Misch.

Discussion: https://postgr.es/m/20250116010051.f3.nmisch@google.com
Backpatch-through: 13
---
 src/backend/access/transam/twophase.c | 16 ++++++++--------
 src/test/recovery/t/009_twophase.pl   | 25 +------------------------
 2 files changed, 9 insertions(+), 32 deletions(-)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index 9f1616c8773..16848fa226c 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -2156,40 +2156,40 @@ ProcessTwoPhaseBuffer(TransactionId xid,
 	if (!fromdisk)
 		Assert(prepare_start_lsn != InvalidXLogRecPtr);
 
-	/* Reject XID if too new */
-	if (TransactionIdFollowsOrEquals(xid, origNextXid))
+	/* Already processed? */
+	if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
 	{
 		if (fromdisk)
 		{
 			ereport(WARNING,
-					(errmsg("removing future two-phase state file for transaction %u",
+					(errmsg("removing stale two-phase state file for transaction %u",
 							xid)));
 			RemoveTwoPhaseFile(xid, true);
 		}
 		else
 		{
 			ereport(WARNING,
-					(errmsg("removing future two-phase state from memory for transaction %u",
+					(errmsg("removing stale two-phase state from memory for transaction %u",
 							xid)));
 			PrepareRedoRemove(xid, true);
 		}
 		return NULL;
 	}
 
-	/* Already processed? */
-	if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
+	/* Reject XID if too new */
+	if (TransactionIdFollowsOrEquals(xid, origNextXid))
 	{
 		if (fromdisk)
 		{
 			ereport(WARNING,
-					(errmsg("removing stale two-phase state file for transaction %u",
+					(errmsg("removing future two-phase state file for transaction %u",
 							xid)));
 			RemoveTwoPhaseFile(xid, true);
 		}
 		else
 		{
 			ereport(WARNING,
-					(errmsg("removing stale two-phase state from memory for transaction %u",
+					(errmsg("removing future two-phase state from memory for transaction %u",
 							xid)));
 			PrepareRedoRemove(xid, true);
 		}
diff --git a/src/test/recovery/t/009_twophase.pl b/src/test/recovery/t/009_twophase.pl
index 59c186a1c82..a5686db2526 100644
--- a/src/test/recovery/t/009_twophase.pl
+++ b/src/test/recovery/t/009_twophase.pl
@@ -7,7 +7,7 @@ use warnings;
 
 use PostgresNode;
 use TestLib;
-use Test::More tests => 28;
+use Test::More tests => 27;
 
 my $psql_out = '';
 my $psql_rc  = '';
@@ -527,26 +527,3 @@ $cur_standby->psql(
 is( $psql_out,
 	qq{27|issued to paris},
 	"Check expected t_009_tbl2 data on standby");
-
-###############################################################################
-# Check handling of orphaned 2PC files at recovery.
-###############################################################################
-
-$cur_primary->teardown_node;
-
-# Grab location in logs of primary
-my $log_offset = -s $cur_primary->logfile;
-
-# Create a fake file with a transaction ID large enough to be in the future,
-# then check that the primary is able to start and remove this file at
-# recovery.
-
-my $future_2pc_file = $cur_primary->data_dir . '/pg_twophase/00FFFFFF';
-append_to_file $future_2pc_file, "";
-
-$cur_primary->start;
-$cur_primary->log_check(
-	"future two-phase file removed at recovery",
-	$log_offset,
-	log_like =>
-	  [qr/removing future two-phase state file for transaction 16777215/]);
-- 
2.30.2