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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
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Previously, only backends, autovacuum workers, and background workers
had an entry in the PMChildFlags array. With this commit, all
postmaster child processes, including all the aux processes, have an
entry. Dead-end backends still don't get an entry, though, and other
processes that don't touch shared memory will never mark their
PMChildFlags entry as active.
We now maintain separate freelists for different kinds of child
processes. That ensures that there are always slots available for
autovacuum and background workers. Previously, pre-authentication
backends could prevent autovacuum or background workers from starting
up, by using up all the slots.
The code to manage the slots in the postmaster process is in a new
pmchild.c source file. Because postmaster.c is just so large.
Assigning pmsignal slot numbers is now pmchild.c's responsibility.
This replaces the PMChildInUse array in pmsignal.c.
Some of the comments in postmaster.c still talked about the "stats
process", but that was removed in commit 5891c7a8ed. Fix those while
we're at it.
Reviewed-by: Andres Freund <[email protected]>
Discussion: https://www.postgresql.org/message-id/[email protected]
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