Re: -HEAD planner issue wrt hash_joins on dbt3 ?

Tom Lane ha scritto:
> Matteo Beccati <php@beccati.com> writes:
>> I cannot see anything bad by using something like that:
>> if (histogram is large/representative enough)
> 
> Well, the question is exactly what is "large enough"?  I feel a bit
> uncomfortable about applying the idea to a histogram with only 10
> entries (especially if we ignore two of 'em).  With 100 or more,
> it sounds all right.  What's the breakpoint?

Yes, I think 100-200 could be a good breakpoint. I don't actually know 
what is the current usage of SET STATISTICS, I usually set it to 1000 
for columns which need more precise selectivity.

The breakpoint could be set even higher (500?) so there is space to 
increase statistics without enabling the histogram check, but I don't 
feel very comfortable though suggesting this kind of possibly 
undocumented side effect...


Best ragards
--
Matteo Beccati
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