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Re: vacuum analyze feedback

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Ed Loehr <eloehr(at)austin(dot)rr(dot)com>
Cc: pghackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: vacuum analyze feedback
Date: 2000-05-25 19:54:40
Message-ID: 200005251954.PAA05479@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
> Bruce Momjian wrote:
> > 
> > > I know this topic has been rehashed a million times, but I just wanted to
> > > add one datapoint.  I have a database (150 tables, less than 20K tuples
> > > in any one table) which I 'vacuum analyze'*HOURLY*, blocking all access,
> > > and I still see frequent situations where my query times bloat by roughly
> > > 300% (4 times slower) in the intervening time between vacuums.  All this
> > > is to say that I think a more strategic implementation of the
> > > functionality of vacuum analyze (specifically, non-batched, automated,
> > > on-the-fly vacuuming/analyzing) would be a major "value add".  I haven't
> > > educated myself as to the history of it, but I do wonder why the
> > > performance focus is not on this.  I'd imagine it would be a performance
> > > hit (which argues for making it optional), but I'd gladly take a 10%
> > > performance hit over the current highly undesireable degradation.  You
> > > could do a whole lotta optimization on the planner/parser/executor and
> > > not get close to the end-user-perceptible gains from fixing this
> > > problem...
> > 
> > Vadim is planning over-write storage manager in 7.2 which will allow
> > expired tuples to be reunsed without vacuum.
> 
> Sorry, I missed that in prior threads...that would be good.
> 
> > Or is the ANALYZE the issue for you?  
> 
> Both, actually.  More specifically, blocking end-user access during
> vacuum, and degraded end-user performance as pg_statistics diverge from
> reality.  Both are losses of service from the system.
> 
> > You need hourly statistics?
> 
> My unstated point was that hourly stats have turned out *not* to be
> nearly good enough in my case.  Better would be if the system was smart
> enough to recognize when the outcome of a query/plan was sufficiently
> divergent from statistics to warrant a system-initiated analyze (or
> whatever form it would take).  I'll probably end up doing this detection
> from the app/client side, but that's not the right place for it, IMO.

Yes, I think eventually, we need to feed information about actual query
results back into the optimizer for use in later queries.

-- 
  Bruce Momjian                        |  http://www.op.net/~candle
  pgman(at)candle(dot)pha(dot)pa(dot)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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