| From: | Florian Pflug <fgp(dot)phlo(dot)org(at)gmail(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Gregory Stark <stark(at)enterprisedb(dot)com>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org> |
| Subject: | Re: HOT patch - version 15 |
| Date: | 2007-09-10 18:05:23 |
| Message-ID: | 46E58763.6030508@gmail.com |
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| Lists: | pgsql-patches |
Bruce Momjian wrote:
> Looking at the patch I see:
>
> + /*
> + * Mark the page as clear of prunable tuples. If we find a tuple which
> + * may become prunable, we shall set the hint again.
> + */
> + PageClearPrunable(page);
>
> I like the idea of the page hint bit, but my question is if there is a
> long-running transaction, isn't each SELECT going to try to defragment a
> page over and over again because there is still something prunable on
> the page?
Maybe that risk could be lowered if instead of a flag, we stored the
minimal global xmin needed to prune at least one tuple.
greetings, Florian Pflug
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