Re: cheaper snapshots

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Hannu Krosing <hannu(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: cheaper snapshots
Date: 2011-07-28 14:23:33
Message-ID: CA+TgmoYOiHH=w4TNjUhmABKfuVYCRY9MeLLm0A2biSK+yFjf9A@mail.gmail.com
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On Thu, Jul 28, 2011 at 10:17 AM, Hannu Krosing <hannu(at)2ndquadrant(dot)com> wrote:
> My hope was, that this contention would be the same than simply writing
> the WAL buffers currently, and thus largely hidden by the current WAL
> writing sync mechanisma.
>
> It really covers just the part which writes commit records to WAL, as
> non-commit WAL records dont participate in snapshot updates.

I'm confused by this, because I don't think any of this can be done
when we insert the commit record into the WAL stream. It has to be
done later, at the time we currently remove ourselves from the
ProcArray. Those things need not happen in the same order, as I noted
in my original post.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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