Re: Analyze and vacuum, they are sort of mandatory....

if we had a pg_vacuum table that had the last timestamp of a vacuum/analyze for each table and the stats looked like 
the default, why not just print a warning message out to the user?




---------- Original Message -----------
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter_e@gmx.net>
Cc: "Mark Woodward" <pgsql@mohawksoft.com>, pgsql-hackers@postgresql.org
Sent: Sun, 12 Feb 2006 11:18:03 -0500
Subject: Re: [HACKERS] Analyze and vacuum, they are sort of mandatory.... 

> Peter Eisentraut <peter_e@gmx.net> writes:
> > Yes, that is what autovacuum does.  It detects changes in the database 
> > and runs analyze if failing to do so would cause PostgreSQL to behave 
> > badly.  I don't know why it's not turned on by default.
> 
> Conservatism.  It may well be on by default in some future release,
> but that's not happening in the first release where the code exists
> at all.
> 
> autovacuum isn't a 100% solution to the sort of problems Mark is
> complaining about anyway: on a freshly-loaded table you could get bad
> plans because autovacuum hadn't gotten to it yet.
> 
> One thing we could consider doing is boosting up the default no-stats
> assumption about the number of distinct values in a column, to the point
> where the planner wouldn't try a hash aggregate unless it had actual
> stats.  However, I'm unsure what negative side-effects that might have.
> 
>             regards, tom lane
> 
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------- End of Original Message -------