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Re: getting to beta

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: Dan Ports <drkp(at)csail(dot)mit(dot)edu>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: getting to beta
Date: 2011-04-07 03:52:16
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Wed, Apr 6, 2011 at 6:32 PM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> The real fix for this problem is probably to have the ability to
>> actually return memory to the shared pool, rather than having
>> everyone grab as they need it until there's no more and never give
>> back. But that's not going to happen in 9.1, so the question is
>> whether this is a sufficiently serious problem that we ought to
>> impose the proposed stopgap fix between now and whenever we do
>> that.
> There is a middle course between leaving the current approach of
> preallocating half the maximum size and leaving the other half up
> for grabs and the course Heikki proposes of making the maximum a
> hard limit.  I submitted a patch to preallocate the maximum, so a
> request for a particular HTAB object will never get "out of shared
> memory" unless it is past its maximum:
> That would leave some extra which is factored into the calculations
> up for grabs, but each table would be guaranteed at least its
> maximum number of entries.  This seems pretty safe to me, and not
> very invasive.  We could always revisit in this 9.2 if that's not
> good enough.

OK, I agree.  We certainly can't have a temporary demand for predicate
locks starve out heavyweight locks for the rest of the postmaster
lifetime, or visca versa.  So we need to do at least that much.

Robert Haas
The Enterprise PostgreSQL Company

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