| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>, "Gregory Stark" <stark(at)enterprisedb(dot)com>, "Bruce Momjian" <bruce(at)momjian(dot)us>, "PostgreSQL-patches" <pgsql-patches(at)postgresql(dot)org> |
| Subject: | Re: HOT patch - version 15 |
| Date: | 2007-09-06 19:36:27 |
| Message-ID: | 1134.1189107387@sss.pgh.pa.us |
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| Lists: | pgsql-patches |
I wrote:
> Hmm ... also check commit status (pg_clog access). I've always thought
> that those things couldn't be done in bgwriter, because it wasn't
> running real transactions, but right at the moment I can't see that
> there is any obstacle. Perhaps that meme dates from a time when
> GetOldestXmin didn't work outside a transaction?
On further thought, I think what I'm remembering is that full-scale
VACUUM can't work inside bgwriter, because you need to take table-level
locks and worry about index vs heap consistency. But as long as HOT
pruning involves only a single heap page I see no need for it to take
more than the buffer-level locks on that page.
regards, tom lane
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