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Re: Parallel query execution

From: Claudio Freire <klaussfreire(at)gmail(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Stephen Frost <sfrost(at)snowman(dot)net>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Parallel query execution
Date: 2013-01-16 02:36:55
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Lists: pgsql-hackers
On Tue, Jan 15, 2013 at 8:19 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> Given our row-based storage architecture, I can't imagine we'd do
>> anything other than take a row-based approach to this..  I would think
>> we'd do two things: parallelize based on partitioning, and parallelize
>> seqscan's across the individual heap files which are split on a per-1G
>> boundary already.  Perhaps we can generalize that and scale it based on
>> the number of available processors and the size of the relation but I
>> could see advantages in matching up with what the kernel thinks are
>> independent files.
> The 1GB idea is interesting.  I found in pg_upgrade that file copy would
> just overwhelm the I/O channel, and that doing multiple copies on the
> same device had no win, but those were pure I/O operations --- a
> sequential scan might be enough of a mix of I/O and CPU that parallelism
> might help.

AFAIR, synchroscans were introduced because multiple large sequential
scans were counterproductive (big time).

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