Re: stats_block_level

Satoshi Nagayasu <nagayasus@nttdata.co.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