Re: vacuum analyze feedback

> 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.

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