Re: [GENERAL] Idea for the statistics collector

Added to TODO:
* Add tool to query pg_stat_* tables and report indexes that aren't needed  or tables that might need indexes

---------------------------------------------------------------------------

Christopher Kings-Lynne wrote:
> I was thinking of writing a command line tool like 'pgtune' that looks at
> the stats views and will generate SQL code for, or do automatically the
> following:
> 
> * Dropping indices that are never used
> * Creating appropriate indices to avoid large, expensive sequential scans.
> 
> This would put us in the 'mysql makes my indices for me by magic' league -
> but would be far more powerful and flexible.  How to do multikey indices is
> beyond me tho.
> 
> *sigh* I'm recovering from a septoplasty on my nose atm, so I might have
> some time to do some coding!
> 
> Chris
> 
> ----- Original Message -----
> From: "Bruce Momjian" <pgman@candle.pha.pa.us>
> To: "Martijn van Oosterhout" <kleptog@svana.org>
> Cc: "PostgreSQL-development" <pgsql-hackers@postgresql.org>
> Sent: Friday, June 21, 2002 10:50 AM
> Subject: Re: [HACKERS] [GENERAL] Idea for the statistics collector
> 
> 
> > Martijn van Oosterhout wrote:
> > > Since it's currently all for collecting statistics on tables, why can't
> it
> > > collect another type of statistic, like:
> > >
> > > - How often the estimator gets it wrong?
> > >
> > > At the end of an index scan, the executor could compare the number of
> rows
> > > returned against what was estimated, and if it falls outside a certain
> > > range, flag it.
> > >
> > > Also, the average ratio of rows coming out of a distinct node vs the
> number
> > > going in.
> > >
> > > For a join clause, the amount of correlation between two columns (hard).
> > >
> > > etc
> > >
> > > Ideally, the planner could then use this info to make better plans.
> > > Eventually, the whole system could become somewhat self-tuning.
> > >
> > > Does anyone see any problems with this?
> >
> > [ Discussion moved to hackers.]
> >
> > I have thought that some type of feedback from the executor back into
> > the optimizer would be a good feature.  Not sure how to do it, but your
> > idea makes sense.  It certainly could update the table statistics after
> > a sequential scan.
> >
> > --
> >   Bruce Momjian                        |  http://candle.pha.pa.us
> >   pgman@candle.pha.pa.us               |  (610) 853-3000
> >   +  If your life is a hard drive,     |  830 Blythe Avenue
> >   +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026
> >
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> 
> 
> 
> 
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> 

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
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