Re: Improvement of procArray.xmin for VACUUM

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.

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>
> "Tom Lane" <tgl@sss.pgh.pa.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@momjian.us>          http://momjian.us
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