From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Ants Aasma <ants(at)cybertec(dot)at> |
Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Josh Berkus <josh(at)agliodbs(dot)com>, PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: postgresql latency & bgwriter not doing its job |
Date: | 2014-09-04 17:01:03 |
Message-ID: | CA+TgmoY6uq=bphJeFDrNZUsqtYHr5t0GAR=RefWE3v9Cj_8G1g@mail.gmail.com |
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On Thu, Sep 4, 2014 at 3:09 AM, Ants Aasma <ants(at)cybertec(dot)at> wrote:
> On Thu, Sep 4, 2014 at 12:36 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
>> It's imo quite clearly better to keep it allocated. For one after
>> postmaster started the checkpointer successfully you don't need to be
>> worried about later failures to allocate memory if you allocate it once
>> (unless the checkpointer FATALs out which should be exceedingly rare -
>> we're catching ERRORs). It's much much more likely to succeed
>> initially. Secondly it's not like there's really that much time where no
>> checkpointer isn't running.
>
> In principle you could do the sort with the full sized array and then
> compress it to a list of buffer IDs that need to be written out. This
> way most of the time you only need a small array and the large array
> is only needed for a fraction of a second.
It's not the size of the array that's the problem; it's the size of
the detonation when the allocation fails.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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