Re: [HACKERS] nested loops in joins, ambiguous rewrite rules

> >We turn on geqo at 8 relations.  Try:  > >    SET GEQO TO 4 >
> >and try the query again.  Let us know.
> 
> Well isn't that something!  Thanks so much for your help!
> 
> I set the GEQO variable to 4 and now the 11.5 minute query
> executes in 6 seconds with this query plan:
> 
> Hash Join  (cost=21.99 size=152 width=124)   width=16)
> 
> 
> Are there any recommendations about what value *ought* to be
> set for GEQO?  It seems to me like 'ON=8' is pretty high -- for
> us, it meant that UNLESS we explicity set that variable for
> every JOIN query of 6-7 tables, the joins were going to bog down
> to a total crawl, while sending memory and CPU consumption
> through the roof (roughly 22MB and 90-95%, respectively, for
> the entire query-processing period).

We have toyed with lowering it to 6.  I think someone said that was too
low, but obviously, some queries need a value of 6 or lower.  I don't
understand when that is the case, though.  Any comments from anyone?

I believe the GEQO README was moved into the documentation in docs.  It
used to be there, but is no longer.


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