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.

Regards,
Ed Loehr