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From: Greg Smith <gsmith@gregsmith.com>
To: pgsql-performance@postgresql.org
Subject: Re: I/O on select count(*)
Date: Sun, 18 May 2008 01:28:26 -0400 (EDT)
Message-ID: <Pine.GSO.4.64.0805180113450.8667@westnet.com> (raw)
In-Reply-To: <18382.1210992302@sss.pgh.pa.us>
References: <920841.71690.qm@web44808.mail.sp1.yahoo.com>
	<482B1D5F.EE98.0025.0@wicourts.gov>
	<Pine.GSO.4.64.0805142133250.27290@westnet.com>
	<20080515020553.GN9838@alvh.no-ip.org>
	<Pine.LNX.4.64.0805151245360.16756@aragorn.flymine.org>
	<20080515155232.GC8221@alvh.no-ip.org>
	<Pine.GSO.4.64.0805161118210.4987@westnet.com>
	<20080516201528.GJ13061@alvh.no-ip.org>
	<18382.1210992302@sss.pgh.pa.us>

I just collected all the good internals information included in this 
thread and popped it onto http://wiki.postgresql.org/wiki/Hint_Bits where 
I'll continue to hack away at the text until it's readable.  Thanks to 
everyone who answered my questions here, that's good progress toward 
clearing up a very underdocumented area.

I note a couple of potential TODO items not on the official list yet that 
came up during this discussion:

-Smooth latency spikes when switching commit log pages by preallocating 
cleared pages before they are needed

-Improve bulk loading by setting "frozen" hint bits for tuple inserts 
which occur within the same database transaction as the creation of the 
table into which they're being inserted

Did I miss anything?  I think everything brought up falls either into one 
of those two or the existing "Consider having the background writer update 
the transaction status hint bits..." TODO.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD



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