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Re: Dead Space Map for vacuum

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: 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: 2006-12-28 15:48:20
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Lists: pgsql-hackers
Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> I experimented with a different DSM design last winter. I got busy with 
> other things and never posted it AFAIR, but the idea was to store a 
> bitmap in the special area on every 32k heap page. That had some advantages:

> * doesn't require a new dedicated shared memory area that needs to be 
> allocated and tuned.
> * doesn't introduce a (single) new global lwlock that might become hotspot.

I agree with doing something along that line (not necessarily with
putting the bits into existing heap pages, but anyway with keeping the
information on disk not in shared memory).  Our experience with the
existing FSM design has been uniformly negative; so I don't wish to add
still another shared memory area that requires tricky manual size
tuning.  I think sooner or later we'll need to redesign FSM so it's not
kept in a fixed-size shared memory area.  Let's not make that mistake

			regards, tom lane

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