v1-0001-Wake-up-autovacuum-launcher-from-postmaster-when-.patch

From ab4362c9e85ad4ad288c80042b7b862bccd2a326 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Thu, 8 Jan 2026 21:36:32 +0200
Subject: [PATCH v1 1/1] Wake up autovacuum launcher from postmaster when a
 worker exits

When an autovacuum worker exits, the launcher needs to be notified
with SIGUSR2, so that it can rebalance and possibly launch a new
worker. The launcher must be notified only after the worker has
finished ProcKill(), so that the worker slot is available for a new
worker. Before this commit, the autovacuum worker was responsible for
that, which required a slightly complicated dance to pass the
launcher's PID from FreeWorkerInfo() to ProcKill() in a global
variable.

Simplify that by moving the responsibility of the signaling to the
postmaster. The postmaster was already doing it when it failed to fork
a worker process, so it seems logical to make it responsible for
notifying the launcher on worker exit too. That's also how the
notification on background worker exit is done.
---
 src/backend/postmaster/autovacuum.c | 22 ----------------------
 src/backend/postmaster/postmaster.c |  8 ++++++++
 src/backend/storage/lmgr/proc.c     |  4 ----
 src/include/postmaster/autovacuum.h |  3 ---
 4 files changed, 8 insertions(+), 29 deletions(-)

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 3e507d23cc9..22379de1e31 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -323,9 +323,6 @@ avl_dbase  *avl_dbase_array;
 /* Pointer to my own WorkerInfo, valid on each worker */
 static WorkerInfo MyWorkerInfo = NULL;
 
-/* PID of launcher, valid only in worker while shutting down */
-int			AutovacuumLauncherPid = 0;
-
 static Oid	do_start_worker(void);
 static void ProcessAutoVacLauncherInterrupts(void);
 pg_noreturn static void AutoVacLauncherShutdown(void);
@@ -1604,11 +1601,6 @@ AutoVacWorkerMain(const void *startup_data, size_t startup_data_len)
 		do_autovacuum();
 	}
 
-	/*
-	 * The launcher will be notified of my death in ProcKill, *if* we managed
-	 * to get a worker slot at all
-	 */
-
 	/* All done, go away */
 	proc_exit(0);
 }
@@ -1623,20 +1615,6 @@ FreeWorkerInfo(int code, Datum arg)
 	{
 		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
 
-		/*
-		 * Wake the launcher up so that he can launch a new worker immediately
-		 * if required.  We only save the launcher's PID in local memory here;
-		 * the actual signal will be sent when the PGPROC is recycled.  Note
-		 * that we always do this, so that the launcher can rebalance the cost
-		 * limit setting of the remaining workers.
-		 *
-		 * We somewhat ignore the risk that the launcher changes its PID
-		 * between us reading it and the actual kill; we expect ProcKill to be
-		 * called shortly after us, and we assume that PIDs are not reused too
-		 * quickly after a process exits.
-		 */
-		AutovacuumLauncherPid = AutoVacuumShmem->av_launcherpid;
-
 		dlist_delete(&MyWorkerInfo->wi_links);
 		MyWorkerInfo->wi_dboid = InvalidOid;
 		MyWorkerInfo->wi_tableoid = InvalidOid;
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 921d73226d6..d6133bfebc6 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -2664,6 +2664,14 @@ CleanupBackend(PMChild *bp,
 	if (bp_bgworker_notify)
 		BackgroundWorkerStopNotifications(bp_pid);
 
+	/*
+	 * If it was an autovacuum worker, wake up the launcher so that it can
+	 * immediately launch a new worker or rebalance to cost limit setting of
+	 * the remaining workers.
+	 */
+	if (bp_bkend_type == B_AUTOVAC_WORKER && AutoVacLauncherPMChild != NULL)
+		signal_child(AutoVacLauncherPMChild, SIGUSR2);
+
 	/*
 	 * If it was a background worker, also update its RegisteredBgWorker
 	 * entry.
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 66274029c74..063826ae576 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -1035,10 +1035,6 @@ ProcKill(int code, Datum arg)
 	ProcGlobal->spins_per_delay = update_spins_per_delay(ProcGlobal->spins_per_delay);
 
 	SpinLockRelease(ProcStructLock);
-
-	/* wake autovac launcher if needed -- see comments in FreeWorkerInfo */
-	if (AutovacuumLauncherPid != 0)
-		kill(AutovacuumLauncherPid, SIGUSR2);
 }
 
 /*
diff --git a/src/include/postmaster/autovacuum.h b/src/include/postmaster/autovacuum.h
index e43067d0260..5aa0f3a8ac1 100644
--- a/src/include/postmaster/autovacuum.h
+++ b/src/include/postmaster/autovacuum.h
@@ -44,9 +44,6 @@ extern PGDLLIMPORT int autovacuum_multixact_freeze_max_age;
 extern PGDLLIMPORT double autovacuum_vac_cost_delay;
 extern PGDLLIMPORT int autovacuum_vac_cost_limit;
 
-/* autovacuum launcher PID, only valid when worker is shutting down */
-extern PGDLLIMPORT int AutovacuumLauncherPid;
-
 extern PGDLLIMPORT int Log_autovacuum_min_duration;
 extern PGDLLIMPORT int Log_autoanalyze_min_duration;
 
-- 
2.47.3