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Re: stats_block_level

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Satoshi Nagayasu <nagayasus(at)nttdata(dot)co(dot)jp>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: stats_block_level
Date: 2007-07-27 04:30:55
Message-ID: 7173.1185510655@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Satoshi Nagayasu <nagayasus(at)nttdata(dot)co(dot)jp> writes:
> I think the stats stuff should be on by default even if it causes
> some performance penalty.

> Because when we have performance problems on the production system,
> it needs more performance penalty (about 5%~) to measure the stats
> by turning their params on.

> In real scenario, we always need the performance information,
> so we always need to turn. So I want the performance information
> can be taken by default.

I don't really agree with this argument.  I've been reading
pgsql-performance for some years now, and I can't recall any incident
whatsoever in which we asked somebody for their stats_block_level
numbers.  To be honest I think those numbers are just about useless.

However, in the current state of the system it seems to be nearly
free to collect them if we are collecting row-level stats, and since
that's happening by default as of 8.3, it's probably worth simplifying
the user-visible behavior by collecting both sets of stats if we collect
either.

			regards, tom lane

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