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Re: Parallel query execution

From: Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Parallel query execution
Date: 2013-01-16 00:11:20
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Lists: pgsql-hackers
On Wed, Jan 16, 2013 at 7:14 AM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> I mentioned last year that I wanted to start working on parallelism:
> Years ago I added thread-safety to libpq.  Recently I added two parallel
> execution paths to pg_upgrade.  The first parallel path allows execution
> of external binaries pg_dump and psql (to restore).  The second parallel
> path does copy/link by calling fork/thread-safe C functions.  I was able
> to do each in 2-3 days.
> I believe it is time to start adding parallel execution to the backend.
> We already have some parallelism in the backend:
> effective_io_concurrency and helper processes.  I think it is time we
> start to consider additional options.
> Parallelism isn't going to help all queries, in fact it might be just a
> small subset, but it will be the larger queries.  The pg_upgrade
> parallelism only helps clusters with multiple databases or tablespaces,
> but the improvements are significant.
> I have summarized my ideas by updating our Parallel Query Execution wiki
> page:
> Please consider updating the page yourself or posting your ideas to this
> thread.  Thanks.
Honestly that would be a great feature, and I would be happy helping
working on it.
Taking advantage of parallelism in a server with multiple core, especially
for things like large sorting operations would be great.
Just thinking loudly, but wouldn't it be the role of the planner to
determine if such or such query is worth using parallelism? The executor
would then be in charge of actually firing the tasks in parallel that
planner has determined necessary to do.
Michael Paquier

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