From: | Fabrízio de Royes Mello <fabriziomello(at)gmail(dot)com> |
---|---|
To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com> |
Subject: | Re: [HACKERS] Re: [HACKERS] GSoC 2015 proposal: Improve the performance of “ALTER TABLE .. SET LOGGED / UNLOGGED” statement |
Date: | 2015-07-09 13:39:35 |
Message-ID: | CAFcNs+o7X01y6QT8cQrtog1xru3df93wdVqOzAOSCGOQF4sGkg@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Jul 8, 2015 at 11:37 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> On 2015-07-08 10:58:51 -0300, Fabrízio de Royes Mello wrote:
> > Think in an ETL job that can be use an unlogged table to improve the
load
> > performance, but this job create a "large table" and to guarantee the
data
> > consistency you need to transform it into a regular table, and with the
> > current implementation rewrite the entire heap, toast and indexes.
>
> Don't buy that. The final target relation will usually already have
> content. Also everything but wal_level=minimal will force you to WAL log
> the contents anyway.
If the "wal_level=minimal" we don't need to force the wal log of the
contents. If the "wal_level != minimal" we need just to xlog all the pages,
but in both cases we don't need the extra job to create a new datafiles and
copy the contents between them. So we'll improve performance, or am I
missing something?
Regards,
--
Fabrízio de Royes Mello
Consultoria/Coaching PostgreSQL
>> Timbira: http://www.timbira.com.br
>> Blog: http://fabriziomello.github.io
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>> Github: http://github.com/fabriziomello
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