Flush statistics during idle periods in parallel apply worker.

Parallel apply workers previously failed to report statistics while
waiting for new work in the main loop. This resulted in the stats from the
most recent transaction remaining unbuffered, leading to arbitrary
reporting delays—particularly when streamed transactions were infrequent.

This commit ensures that statistics are explicitly flushed when the worker
is idle, providing timely visibility into accumulated worker activity.

Author: Zhijie Hou <houzj.fnst@fujitsu.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Backpatch-through: 16, where it was introduced
Discussion: https://postgr.es/m/TYRPR01MB1419579F217CC4332B615589594202@TYRPR01MB14195.jpnprd01.prod.outlook.com

diff --git a/src/backend/replication/logical/applyparallelworker.c b/src/backend/replication/logical/applyparallelworker.c
index 2d140e262c11127da0f9b6dac900320dc6e57eca..b70adf342a56da0d611b1c6791512ece35f65603 100644 (file)
--- a/src/backend/replication/logical/applyparallelworker.c
+++ b/src/backend/replication/logical/applyparallelworker.c
@@ -811,6 +811,15 @@ LogicalParallelApplyLoop(shm_mq_handle *mqh)
 
                                if (rc & WL_LATCH_SET)
                                        ResetLatch(MyLatch);
+
+                               /*
+                                * Force stats reporting to avoid long delays. There can be long
+                                * idle gaps before the leader assigns the next transaction, and
+                                * the only opportunity to report stats during such gaps is
+                                * here.
+                                */
+                               if ((rc & WL_TIMEOUT) && !IsTransactionState())
+                                       pgstat_report_stat(true);
                        }
                }
                else