Обсуждение: Plannner favoring nested loop

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Plannner favoring nested loop

От
Abu Mushayeed
Дата:
Hello,
 
I am trying to determine if I can make the planner see that nested loop is very expensive while it is trying to do an plan for a query and not pick that route.
 
Is there a way to this in postgres? I know about the "set enable..." commands. I was wondering if I can do it without the hints.
 
Thanks
Abu

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Re: Plannner favoring nested loop

От
Tom Lane
Дата:
Abu Mushayeed <abumushayeed@yahoo.com> writes:
>   I am trying to determine if I can make the planner see that nested loop is very expensive while it is trying to do
anplan for a query and not pick that route.  

If it's doing that when it shouldn't, it's probably because it's
underestimated the number of rows in the outer relation.  Look to your
stats settings.

            regards, tom lane

Re: Plannner favoring nested loop

От
Abu Mushayeed
Дата:
My default_statistics_target in the postgresql.conf file is set at 250. The tables are vacuumed everyday. Now, does that mean, for each column or only for the column on which index exist, increase the value of "statistics" value, so while analyzing it uses more rows in the sample.
Thanks
Abu
Tom Lane <tgl@sss.pgh.pa.us> wrote:
Abu Mushayeed writes:
> I am trying to determine if I can make the planner see that nested loop is very expensive while it is trying to do an plan for a query and not pick that route.

If it's doing that when it shouldn't, it's probably because it's
underestimated the number of rows in the outer relation. Look to your
stats settings.

regards, tom lane

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