| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com> |
| Cc: | "Jim C(dot) Nasby" <decibel(at)decibel(dot)org>, "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, Robert Treat <xzilla(at)users(dot)sourceforge(dot)net>, pgsql-patches(at)postgresql(dot)org, Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com> |
| Subject: | Re: Have vacuum emit a warning when it runs out of maintenance_work_mem |
| Date: | 2007-05-14 16:54:08 |
| Message-ID: | 13246.1179161648@sss.pgh.pa.us |
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| Lists: | pgsql-patches |
Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Jim C. Nasby wrote:
>> If nothing else, it would likely be
>> worth special-casing an entire page being dead, which is a common case
>> for queue tables. That could be done by making an entry in the page
>> number array with a special offset value.
> That won't work, because someone might add live tuples to the page after
> the 1st vacuum pass. You could only invoke that special case when
> there's no room on the page for new tuples, but that's a hack and not as
> common.
The bitmap case seems to me to be plenty efficient already for an
all-dead page. The regime where my proposal seems to leave something
to be desired is just a few dead tuples per page --- it's not very much
better than the existing code in that case.
regards, tom lane
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