| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
| Cc: | "Florian Pflug" <fgp(dot)phlo(dot)org(at)gmail(dot)com>, "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Bruce Momjian" <bruce(at)momjian(dot)us>, "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>, "Gregory Stark" <stark(at)enterprisedb(dot)com>, "PostgreSQL-patches" <pgsql-patches(at)postgresql(dot)org> |
| Subject: | Re: HOT patch - version 15 |
| Date: | 2007-09-08 20:39:28 |
| Message-ID: | 29293.1189283968@sss.pgh.pa.us |
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| Lists: | pgsql-patches |
"Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> writes:
> Tom argued that following the tuple chain is cheap enough, and might
> even be cheaper than what we have now, that we don't need to prune just
> for the purpose of keeping the chains short. To which I pointed out that
> currently, without HOT, we mark index tuples pointing to dead tuples as
> killed to avoid following them in the future, so HOT without pruning is
> not cheaper than what we have now.
That hack only works in plain indexscans, though, not bitmapped scans.
Anyway, I remain unconvinced that the chains would normally get very
long in the first place, if we could prune when updating.
The we-already-pinned-the-page problem is a bit nasty but may not be
insurmountable.
regards, tom lane
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