From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org> |
Subject: | Re: Improvement of procArray.xmin for VACUUM |
Date: | 2007-03-27 00:50:48 |
Message-ID: | 200703270050.l2R0omk14530@momjian.us |
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Lists: | pgsql-patches |
Gregory Stark wrote:
>
> I have a question about what would happen for a transaction running a command
> like COPY FROM. Is it possible it would manage to arrange to have no live
> snapshots at all? So it would have no impact on concurrent VACUUMs? What about
> something running a large pg_restore?
Interesting idea. If the table had triggers, it would need a snapshot,
but if not, yea, that is certainly possible.
---------------------------------------------------------------------------
>
> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>
> > On the whole though I think we should let this idea go till 8.4;
>
> I tend to agree but for a different reason. I think it's something that will
> open the doors for a lot of new ideas. If we put it in CVS HEAD early in 8.4 I
> think (or hope at any rate) we'll think of at least a few new things we can do
> with the new more precise information it exposes.
>
> Just as an example, if you find you have no live snapshots can you throw out
> the combocid hash? Any tuple you find with a combocid that's been discarded
> that way must predate your current scan and therefore is deleted for you.
>
> --
> Gregory Stark
> EnterpriseDB http://www.enterprisedb.com
>
>
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
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