On 5/1/23 18:33, Robert Haas wrote:
> Why not? It seems like something some people might want to log and
> others not. Running the whole server at DEBUG1 to get this information
> doesn't seem like a suitable answer.
Since the statement is also logged, it could spam the log with huge
queries, which might also be a reason to stop logging this kind of
problems until the issue is fixed.
I attached the patch without the guc anyway just in case.
What I was wondering was whether we would be better off putting this
into the statistics collector, vs. doing it via logging. Both
approaches seem to have pros and cons.
We tried to explore different options with my collegues in another
thread [1]. I feel like both solutions are worthwhile, and would be
helpful. I plan to take a look at the pg_stat_statement patch [2] next.
Since it's my first patch, I elected to choose the easiest solution to
implement first. I also proposed this because I think logging can help
pinpoint a lot of problems at a minimal cost, since it is easy to setup
and exploit for everyone, everywhere
[1]
https://www.postgresql.org/message-id/d657df20-c4bf-63f6-e74c-cb85a81d0...@dalibo.com
[2]
https://www.postgresql.org/message-id/flat/6acbe570-068e-bd8e-95d5-00c737b865e8%40gmail.com
--
Benoit Lobréau
Consultant
http://dalibo.com
From fc71ef40f33f94b0506a092fb5b3dcde6de6d60a Mon Sep 17 00:00:00 2001
From: benoit <benoit.lobr...@dalibo.com>
Date: Tue, 2 May 2023 10:08:00 +0200
Subject: [PATCH] Add logging for exceeded parallel worker slot limits
Procude a log message when a backend attempts to spawn a parallel worker
but fails due to insufficient worker slots. The shortage can stem from
max_worker_processes, max_parallel_worker, or
max_parallel_maintenance_workers. The log message can help database
administrators and developers diagnose performance issues related to
parallelism and optimize the configuration of the system accordingly.
---
src/backend/access/transam/parallel.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/src/backend/access/transam/parallel.c
b/src/backend/access/transam/parallel.c
index b26f2a64fb..c60d1bd739 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -630,6 +630,11 @@ LaunchParallelWorkers(ParallelContext *pcxt)
pcxt->nknown_attached_workers = 0;
}
+ if (pcxt->nworkers_launched < pcxt->nworkers_to_launch)
+ ereport(LOG,
+ (errmsg("Parallel Worker draught during
statement execution: workers spawned %d, requested %d",
+ pcxt->nworkers_launched,
pcxt->nworkers_to_launch)));
+
/* Restore previous memory context. */
MemoryContextSwitchTo(oldcontext);
}
--
2.39.2
