From 2cb9f3a2b70a9182d9b4d45d25e67779b2712ca8 Mon Sep 17 00:00:00 2001 From: Zhijie Hou Date: Thu, 9 Apr 2026 20:11:40 +0800 Subject: [PATCH v3] Fix slotsync worker busy loop causing repeated logical decoding logs. Previously, the slotsync worker could enter a busy loop and emit four logical log messages every 200 ms, even when both the primary and standby were idle. This happened because the worker incorrectly treated certain cases as successful slot updates, causing it to use the minimum sleep interval and repeatedly restart slot syncing. This commit fixes this by ensuring the worker does not treat such cases as updates, allowing it to sleep normally and avoid excessive log output. --- src/backend/replication/logical/slotsync.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c index f90653e5232..527b26d1a2b 100644 --- a/src/backend/replication/logical/slotsync.c +++ b/src/backend/replication/logical/slotsync.c @@ -332,10 +332,15 @@ update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid) slot->data.confirmed_flush = remote_slot->confirmed_lsn; slot->data.catalog_xmin = remote_slot->catalog_xmin; SpinLockRelease(&slot->mutex); + + updated_xmin_or_lsn = true; } else { bool found_consistent_snapshot; + XLogRecPtr old_confirmed_lsn = slot->data.confirmed_flush; + XLogRecPtr old_restart_lsn = slot->data.restart_lsn; + XLogRecPtr old_catalog_xmin = slot->data.catalog_xmin; LogicalSlotAdvanceAndCheckSnapState(remote_slot->confirmed_lsn, &found_consistent_snapshot); @@ -365,9 +370,20 @@ update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid) skip_reason = SS_SKIP_NO_CONSISTENT_SNAPSHOT; } - } - updated_xmin_or_lsn = true; + /* + * The restart_lsn and catalog_xmin may not change when the synced + * slot is building its first consistent snapshot (or cannot build + * one at all), or when the slot on the primary advances + * restart_lsn to an xl_running_xacts record that begins exactly + * at confirmed_flush_lsn (e.g., via pg_logical_slot_peek_xxx), a + * position not reachable by + * LogicalSlotAdvanceAndCheckSnapState(). + */ + updated_xmin_or_lsn = (old_confirmed_lsn != slot->data.confirmed_flush || + old_restart_lsn != slot->data.restart_lsn || + old_catalog_xmin != slot->data.catalog_xmin); + } } /* Update slot sync skip stats */ -- 2.31.1