v1-0001-Allow-old-WALs-to-be-removed-during-REPACK-CONCUR.patch

From 3b4c9a890fdeb854949a36b6be8f1fc00a5edafe Mon Sep 17 00:00:00 2001
From: Zhijie Hou <houzj.fnst@fujitsu.com>
Date: Fri, 10 Apr 2026 16:24:55 +0800
Subject: [PATCH v1] Allow old WALs to be removed during REPACK CONCURRENTLY

---
 src/backend/commands/repack_worker.c      | 14 +++++++++++++-
 src/backend/replication/logical/logical.c |  4 +++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 5bd020e0184..50f000ca6df 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -394,12 +394,24 @@ decode_concurrent_changes(LogicalDecodingContext *ctx,
 
 			/*
 			 * If WAL segment boundary has been crossed, inform the decoding
-			 * system that the catalog_xmin can advance.
+			 * system that the slot can advance.
+			 *
+			 * Once REPACK begins copying data to the new table, the logical
+			 * decoding machinery prevents the slot from advancing beyond the
+			 * oldest running transaction (which is the REPACK transaction
+			 * itself). As a result, restart_lsn and catalog_xmin can no longer
+			 * advance automatically.
+			 *
+			 * To allow old WAL files to be recycled, we manually advance the
+			 * slot each time a WAL segment boundary is crossed. We do not
+			 * advance catalog_xmin here because the REPACK transaction anyway
+			 * holds a snapshot that prevents catalog tuple removal.
 			 */
 			end_lsn = ctx->reader->EndRecPtr;
 			XLByteToSeg(end_lsn, segno_new, wal_segment_size);
 			if (segno_new != repack_current_segment)
 			{
+				LogicalIncreaseRestartDecodingForSlot(end_lsn, end_lsn);
 				LogicalConfirmReceivedLocation(end_lsn);
 				elog(DEBUG1, "REPACK: confirmed receive location %X/%X",
 					 (uint32) (end_lsn >> 32), (uint32) end_lsn);
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index d8e02c53558..baa639835f7 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -1913,8 +1913,10 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
 			SpinLockRelease(&MyReplicationSlot->mutex);
 
 			ReplicationSlotsComputeRequiredXmin(false);
-			ReplicationSlotsComputeRequiredLSN();
 		}
+
+		if (updated_restart)
+			ReplicationSlotsComputeRequiredLSN();
 	}
 	else
 	{
-- 
2.53.0.windows.2