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Allow changing autovacuum_max_workers without restarting.

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This commit introduces a new parameter named
autovacuum_worker_slots that controls how many autovacuum worker
slots to reserve during server startup.  Modifying this new
parameter's value does require a server restart, but it should
typically be set to the upper bound of what you might realistically
need to set autovacuum_max_workers.  With that new parameter in
place, autovacuum_max_workers can now be changed with a SIGHUP
(e.g., pg_ctl reload).

If autovacuum_max_workers is set higher than
autovacuum_worker_slots, a WARNING is emitted, and the server will
only start up to autovacuum_worker_slots workers at a given time.
If autovacuum_max_workers is set to a value less than the number of
currently-running autovacuum workers, the existing workers will
continue running, but no new workers will be started until the
number of running autovacuum workers drops below
autovacuum_max_workers.

Reviewed-by: Sami Imseih, Justin Pryzby, Robert Haas, Andres Freund, Yogesh Sharma
Discussion: https://postgr.es/m/20240410212344.GA1824549%40nathanxps13
This commit is contained in:
Nathan Bossart
2025-01-06 15:01:22 -06:00
parent 5e68f61192
commit c758119e5b
11 changed files with 117 additions and 31 deletions
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6
src/backend/utils/init/postinit.c
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@@ -547,15 +547,15 @@ InitializeMaxBackends(void)
Assert(MaxBackends == 0);
/* Note that this does not include "auxiliary" processes */
MaxBackends = MaxConnections + autovacuum_max_workers +
MaxBackends = MaxConnections + autovacuum_worker_slots +
max_worker_processes + max_wal_senders + NUM_SPECIAL_WORKER_PROCS;
if (MaxBackends > MAX_BACKENDS)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("too many server processes configured"),
errdetail("\"max_connections\" (%d) plus \"autovacuum_max_workers\" (%d) plus \"max_worker_processes\" (%d) plus \"max_wal_senders\" (%d) must be less than %d.",
MaxConnections, autovacuum_max_workers,
errdetail("\"max_connections\" (%d) plus \"autovacuum_worker_slots\" (%d) plus \"max_worker_processes\" (%d) plus \"max_wal_senders\" (%d) must be less than %d.",
MaxConnections, autovacuum_worker_slots,
max_worker_processes, max_wal_senders,
MAX_BACKENDS - (NUM_SPECIAL_WORKER_PROCS - 1))));
}