| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Simon Riggs" <simon(at)2ndquadrant(dot)com> |
| Cc: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Gavin Sherry" <swm(at)linuxworld(dot)com(dot)au>, "ITAGAKI Takahiro" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Dead Space Map for vacuum |
| Date: | 2006-12-29 21:41:11 |
| Message-ID: | 17760.1167428471@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
"Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> On Fri, 2006-12-29 at 10:49 -0500, Tom Lane wrote:
>> Counterexample: table in which all tuples exceed half a page.
> Current FSM code will ignore those too, if they are less than the
> average size of the tuple so far requested. Thats a pretty wierd
> counterexample, even if it is a case that needs handling.
Better read it again. The number that's passed to the FSM is the
free space *after* vacuuming, which in this scenario will be
BLCKSZ-less-page-header. This case is not broken now, but it will
be if we adopt your proposal.
regards, tom lane
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