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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Daniel Farina <daniel@heroku.com>
Cc: Craig Ringer <ringerc@ringerc.id.au>
Cc: Harold A. Giménez <harold.gimenez@gmail.com>
Subject: Re: [PERFORM] DELETE vs TRUNCATE explanation
Date: Thu, 19 Jul 2012 17:02:08 -0400
Message-ID: <13265.1342731728@sss.pgh.pa.us> (raw)
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References: <4FFCCAC4.4030503@ringerc.id.au>
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	<CA+TgmoagwPY! G8QO3ykccp4_dpYy_Y_KKzF4QQB <CA+TgmobkLaBJa5+HG9VsV_MNJGiVEBymio-msdKETZiPk1q36Q@mail.gmail.com>

Robert Haas <robertmhaas@gmail.com> writes:
> What if we change the hash table to have RelFileNode as the key and an
> array of MAX_FORKNUM bitmapsets as the value?  Then when you get a
> "forget" request, you can just zap all the sets to empty.

Hm ... the only argument I can really make against that is that there'll
be no way to move such a table into shared memory; but there's probably
little hope of that anyway, given points made upthread.  The bitmapset
manipulations are a bit tricky but solvable, and I agree there's
something to be said for not tying this stuff so closely to the
mechanism for relfilenode recycling.

			regards, tom lane



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