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Re: Random penalties on GIN index updates?

From: Jesper Krogh <jesper(at)krogh(dot)cc>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Random penalties on GIN index updates?
Date: 2009-10-22 04:57:49
Message-ID: 4ADFE64D.1080608@krogh.cc (view raw or flat)
Thread:
Lists: pgsql-performance
Robert Haas wrote:
> On Wed, Oct 21, 2009 at 2:35 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Jesper Krogh <jesper(at)krogh(dot)cc> writes:
>>> What I seems to miss a way to make sure som "background" application is
>>> the one getting the penalty, so a random user doing a single insert
>>> won't get stuck. Is that doable?
>> You could force a vacuum every so often, but I don't think that will
>> help the locking situation.  You really need to back off work_mem ---
>> 512MB is probably not a sane global value for that anyway.
> 
> Yeah, it's hard to imagine a system where that doesn't threaten all
> kinds of other bad results.  I bet setting this to 4MB will make this
> problem largely go away.
> 
> Arguably we shouldn't be using work_mem to control this particular
> behavior, but...

I came from Xapian, where you only can have one writer process, but
batching up in several GB's improved indexing performance dramatically.
Lowering work_mem to 16MB gives "batches" of 11.000 documents and stall
between 45 and 90s.  ~ 33 docs/s

-- 
Jesper

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