Re: Parallel tuplesort (for parallel B-Tree index creation)

From: Peter Geoghegan <pg(at)heroku(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Subject: Re: Parallel tuplesort (for parallel B-Tree index creation)
Date: 2016-09-26 19:40:05
Message-ID: CAM3SWZSxvacUK8o22Jk0ufSUqW-nVPaBYcLnrse_hMHFbYN84g@mail.gmail.com
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On Mon, Sep 26, 2016 at 6:58 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> That requires some kind of mutual exclusion mechanism, like an LWLock.
>
> No, it doesn't. Shared memory queues are single-reader, single-writer.

The point is that there is a natural dependency when merging is
performed eagerly within the leader. One thing needs to be in lockstep
with the others. That's all.

--
Peter Geoghegan

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