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Re: autovacuum launcher using InitPostgres

From: Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: autovacuum launcher using InitPostgres
Date: 2009-08-31 21:42:16
Message-ID: m21vmr64p3.fsf@hi-media.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Hi,

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> The user may not care about the difference, but there's a point in
>> having the limit be the simpler concept of "this is the maximum amount
>> of processes running vacuum at any time".  The launcher is very
>> uninteresting to users.

Adding to this, the launcher will not consume maintenance_work_mem
whereas each worker is able to allocate that much, IIUC.

> I committed things that way, but I'm still not convinced that we
> shouldn't expose the launcher in pg_stat_activity.  The thing that
> is bothering me is that it is now able to take locks and potentially
> could block some other process or even participate in a deadlock.
> Do we really want to have entries in pg_locks that don't match any
> entry in pg_stat_activity?

Having the launcher locks show as such gets my vote too, but then I'm
following on your opinion that a launcher ain't a worker and that users
need to know about it. 

Let's keep the autovacuum_max_workers GUC naming, not counting the
"there can be only one" launcher so that we're able to size
maintenance_work_mem.

Regards,
-- 
dim

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