From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 6 Jul 2026 02:37:36 +0000 (+0900)
Subject: Emit a warning when io_min_workers exceeds io_max_workers
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=9d1188f29865e66c4196578501e74e8c815fba8d;p=thirdparty%2Fpostgresql.git

Emit a warning when io_min_workers exceeds io_max_workers

When io_min_workers is set strictly higher than io_max_workers, the
minimum has no effect since the pool will never grow past
io_max_workers.  Previously this was silently accepted, which could
be confusing for users expecting at least io_min_workers workers to
always be running.

In order to avoid noise in the server logs, the following restrictions
are in place:
- The only process printing the WARNING is the IO worker with ID 0, on
startup and reload, which is we know the only process always running
when using IO workers.
- At reload, the message shows only if one of the bounds has changed.

Note that this commit reuses a log message updated by 7905416eef9b.

Author: Baji Shaik <baji.pgdev@gmail.com>
Reviewed-by: Tristan Partin <tristan@partin.io>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/CA+fm-RO_O7-XThg2qjj=ir35x9nOFbZYu07gttqAbM5T88QB4Q@mail.gmail.com
---

diff --git a/src/backend/storage/aio/method_worker.c b/src/backend/storage/aio/method_worker.c
index 63e34d66690..cf75b2816b7 100644
--- a/src/backend/storage/aio/method_worker.c
+++ b/src/backend/storage/aio/method_worker.c
@@ -662,6 +662,27 @@ pgaio_worker_can_timeout(void)
 	return true;
 }
 
+/*
+ * Emit a WARNING if io_min_workers > io_max_workers, since the worker
+ * pool will never exceed io_max_workers regardless of the minimum setting.
+ */
+static void
+check_io_worker_gucs(void)
+{
+	/* Only do the check in one worker, to limit noise */
+	if (MyIoWorkerId != 0)
+		return;
+
+	if (io_min_workers > io_max_workers)
+		ereport(WARNING,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("\"%s\" (%d) should be less than or equal to \"%s\" (%d)",
+						"io_min_workers", io_min_workers,
+						"io_max_workers", io_max_workers),
+				 errdetail("The I/O worker pool will not exceed \"%s\" (%d) workers.",
+						   "io_max_workers", io_max_workers)));
+}
+
 void
 IoWorkerMain(const void *startup_data, size_t startup_data_len)
 {
@@ -694,6 +715,8 @@ IoWorkerMain(const void *startup_data, size_t startup_data_len)
 	/* also registers a shutdown callback to unregister */
 	pgaio_worker_register();
 
+	check_io_worker_gucs();
+
 	sprintf(cmd, "%d", MyIoWorkerId);
 	set_ps_display(cmd);
 
@@ -1011,9 +1034,20 @@ IoWorkerMain(const void *startup_data, size_t startup_data_len)
 
 		if (ConfigReloadPending)
 		{
+			int			io_max_workers_prev = io_max_workers;
+			int			io_min_workers_prev = io_min_workers;
+
 			ConfigReloadPending = false;
 			ProcessConfigFile(PGC_SIGHUP);
 
+			/*
+			 * Emit a WARNING if io_min_workers > io_max_workers.  If no bound
+			 * has changed, skip this to avoid too many log messages.
+			 */
+			if (io_min_workers_prev != io_min_workers ||
+				io_max_workers_prev != io_max_workers)
+				check_io_worker_gucs();
+
 			/* If io_max_workers has been decreased, exit highest first. */
 			if (MyIoWorkerId >= io_max_workers)
 				break;