From: | Andres Freund <andres(at)anarazel(dot)de> |
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To: | pgsql-hackers(at)postgresql(dot)org |
Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Joachim Wieland <joe(at)mcknight(dot)de>, Greg Smith <greg(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, José Arthur Benetasso Villanova <jose(dot)arthur(at)gmail(dot)com> |
Subject: | Re: directory archive format for pg_dump |
Date: | 2010-12-16 22:53:21 |
Message-ID: | 201012162353.21655.andres@anarazel.de |
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Lists: | pgsql-hackers |
On Thursday 16 December 2010 23:34:02 Heikki Linnakangas wrote:
> On 17.12.2010 00:29, Andres Freund wrote:
> > On Thursday 16 December 2010 19:33:10 Joachim Wieland wrote:
> >> On Thu, Dec 16, 2010 at 12:48 PM, Heikki Linnakangas
> >>
> >> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> >>> As soon as we have parallel pg_dump, the next big thing is going to be
> >>> parallel dump of the same table using multiple processes. Perhaps we
> >>> should prepare for that in the directory archive format, by allowing
> >>> the data of a single table to be split into multiple files. That way
> >>> parallel pg_dump is simple, you just split the table in chunks of
> >>> roughly the same size, say 10GB each, and launch a process for each
> >>> chunk, writing to a separate file.
> >>
> >> How exactly would you "just split the table in chunks of roughly the
> >> same size" ? Which queries should pg_dump send to the backend? If it
> >> just sends a bunch of WHERE queries, the server would still scan the
> >> same data several times since each pg_dump client would result in a
> >> seqscan over the full table.
> >
> > I would suggest implementing< > support for tidscans and doing it in
> > segment size...
>
> I don't think there's any particular gain from matching the server's
> data file segment size, although 1GB does sound like a good chunk size
> for this too.
Its noticeable more efficient reading from different files in different processes
in comparison to all hammering the same file.
Andres
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