RE: [HACKERS] Some notes on optimizer cost estimates

> -----Original Message-----
> From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
> 
> > "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > > I've wondered why we cound't analyze database without vacuum.
> > > We couldn't run vacuum light-heartedly because it acquires an
> > > exclusive lock for the target table. 
> > 
> > There is probably no real good reason, except backwards compatibility,
> > why the ANALYZE function (obtaining pg_statistic data) is part of
> > VACUUM at all --- it could just as easily be a separate command that
> > would only use read access on the database.  Bruce is thinking about
> > restructuring VACUUM, so maybe now is a good time to think about
> > splitting out the ANALYZE code too.
> 
> I put it in vacuum because at the time I didn't know how to do such
> things and vacuum already scanned the table.  I just linked on the the
> scan.  Seemed like a good idea at the time.
> 
> It is nice that ANALYZE is done during vacuum.  I can't imagine why you
> would want to do an analyze without adding a vacuum to it.  I guess
> that's why I made them the same command.
> 
> If I made them separate commands, both would have to scan the table,
> though the analyze could do it without the exclusive lock, which would
> be good.
>

The functionality of VACUUM and ANALYZE is quite different.
I don't prefer to charge VACUUM more than now about analyzing
database.  Probably looong lock,more aborts .... 
Various kind of analysis would be possible by splitting out ANALYZE.
Regards.

Hiroshi Inoue
Inoue@tpf.co.jp