v1-0001-Fix-premature-xmin-advancement-during-fast-forwar.patch

From 5327186830024769c2d893fba5859ebbdc04af29 Mon Sep 17 00:00:00 2001
From: Zhijie Hou <houzj.fnst@cn.fujitsu.com>
Date: Tue, 22 Apr 2025 10:58:35 +0800
Subject: [PATCH v1 1/2] Fix premature xmin advancement during fast forward
 decoding

Fast forward decoding could lead to premature advancement of catalog_xmin,
resulting in required catalog data being removed by vacuum. The issue arise
because we do not build a base snapshot when decoding changes during fast
forward mode, preventing reference to the minimum transaction ID that remains
visible in the snapshot when determining the candidate for catalog_xmin. As a
result, catalog_xmin was directly advanced to the oldest running transaction ID
found in the latest running_xacts record.

To resolve this, the commit allows the base snapshot to be built during fast
forward decoding.
---
 src/backend/replication/logical/decode.c | 37 ++++++++++++++++--------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 78f9a0a11c4..8dc467a8bb3 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -412,19 +412,24 @@ heap2_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 	/*
 	 * If we don't have snapshot or we are just fast-forwarding, there is no
-	 * point in decoding changes.
+	 * point in decoding data changes. However, it's crucial to build the base
+	 * snapshot during fast-forward mode (as done in SnapBuildProcessChange())
+	 * because the snapshot's minimum visible transaction ID (xmin) must be
+	 * referenced when determining the candidate catalog_xmin for the
+	 * replication slot.
 	 */
-	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
-		ctx->fast_forward)
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
 		return;
 
 	switch (info)
 	{
 		case XLOG_HEAP2_MULTI_INSERT:
-			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+			if (SnapBuildProcessChange(builder, xid, buf->origptr) &&
+				!ctx->fast_forward)
 				DecodeMultiInsert(ctx, buf);
 			break;
 		case XLOG_HEAP2_NEW_CID:
+			if (!ctx->fast_forward)
 			{
 				xl_heap_new_cid *xlrec;
 
@@ -471,16 +476,20 @@ heap_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 	/*
 	 * If we don't have snapshot or we are just fast-forwarding, there is no
-	 * point in decoding data changes.
+	 * point in decoding data changes. However, it's crucial to build the base
+	 * snapshot during fast-forward mode (as done in SnapBuildProcessChange())
+	 * because the snapshot's minimum visible transaction ID (xmin) must be
+	 * referenced when determining the candidate catalog_xmin for the
+	 * replication slot.
 	 */
-	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT ||
-		ctx->fast_forward)
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
 		return;
 
 	switch (info)
 	{
 		case XLOG_HEAP_INSERT:
-			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+			if (SnapBuildProcessChange(builder, xid, buf->origptr) &&
+				!ctx->fast_forward)
 				DecodeInsert(ctx, buf);
 			break;
 
@@ -491,17 +500,20 @@ heap_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 			 */
 		case XLOG_HEAP_HOT_UPDATE:
 		case XLOG_HEAP_UPDATE:
-			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+			if (SnapBuildProcessChange(builder, xid, buf->origptr) &&
+				!ctx->fast_forward)
 				DecodeUpdate(ctx, buf);
 			break;
 
 		case XLOG_HEAP_DELETE:
-			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+			if (SnapBuildProcessChange(builder, xid, buf->origptr) &&
+				!ctx->fast_forward)
 				DecodeDelete(ctx, buf);
 			break;
 
 		case XLOG_HEAP_TRUNCATE:
-			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+			if (SnapBuildProcessChange(builder, xid, buf->origptr) &&
+				!ctx->fast_forward)
 				DecodeTruncate(ctx, buf);
 			break;
 
@@ -525,7 +537,8 @@ heap_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 			break;
 
 		case XLOG_HEAP_CONFIRM:
-			if (SnapBuildProcessChange(builder, xid, buf->origptr))
+			if (SnapBuildProcessChange(builder, xid, buf->origptr) &&
+				!ctx->fast_forward)
 				DecodeSpecConfirm(ctx, buf);
 			break;
 
-- 
2.30.0.windows.2