From 7c906c5b46f8189a04e67bc550cba33dd3851b6e Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Tue, 25 Feb 2025 09:22:16 +0530 Subject: [PATCH] Doc: Fix pg_copy_logical_replication_slot description. This commit documents that the failover option is not copied when using the pg_copy_logical_replication_slot function. In passing, we modify the comments in the function clarifying the reason for this behavior. Reported-by: Author: Hou Zhijie Reviewed-by: Amit Kapila Backpatch-through: 17, where it was introduced Discussion: https://postgr.es/m/173976850802.682632.11315364077431550250@wrigleys.postgresql.org --- doc/src/sgml/func.sgml | 4 ++++ src/backend/replication/slotfuncs.c | 19 ++++++++++++------- 2 files changed, 16 insertions(+), 7 deletions(-) diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 1c5e4bc5732..d8b27903593 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -29118,6 +29118,10 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset from the same LSN as the source logical slot. Both temporary and plugin are optional; if they are omitted, the values of the source slot are used. + The failover option of the source logical slot + is not copied and is set to false by default. This + is to avoid the risk of being unable to continue logical replication + after failover to standby where the slot is being synchronized. diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c index dd6c1d5a7e3..43c3cc7336b 100644 --- a/src/backend/replication/slotfuncs.c +++ b/src/backend/replication/slotfuncs.c @@ -698,13 +698,18 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot) * hence pass find_startpoint false. confirmed_flush will be set * below, by copying from the source slot. * - * To avoid potential issues with the slot synchronization where the - * restart_lsn of a replication slot can go backward, we set the - * failover option to false here. This situation occurs when a slot - * on the primary server is dropped and immediately replaced with a - * new slot of the same name, created by copying from another existing - * slot. However, the slot synchronization will only observe the - * restart_lsn of the same slot going backward. + * We don't copy the failover option to prevent potential issues with + * slot synchronization. For instance, if a slot was synchronized to + * the standby, then dropped on the primary, and immediately recreated + * by copying from another existing slot with much earlier restart_lsn + * and confirmed_flush_lsn, the slot synchronization would only + * observe the LSN of the same slot moving backward. As slot + * synchronization does not copy the restart_lsn and + * confirmed_flush_lsn backward (see update_local_synced_slot() for + * details), if a failover happens before the primary's slot catches + * up, logical replication cannot continue using the synchronized slot + * on the promoted standby because the slot retains the restart_lsn + * and confirmed_flush_lsn that are much later than expected. */ create_logical_replication_slot(NameStr(*dst_name), plugin,