Re: two queries and dual cpu (perplexed)

Shoaib Burq (VPAC) wrote:
> OK ... so just to clearify...  (and pardon my ignorance):
>
> I need to increase the value of 'default_statistics_target' variable and
> then run VACUUM ANALYZE, right? If so what should I choose for the
> 'default_statistics_target'?
>
> BTW I only don't do any sub-selection on the View.
>
> I have attached the view in question and the output of:
> SELECT oid , relname, relpages, reltuples
>         FROM pg_class ORDER BY relpages DESC;
>
> reg
> shoaib

Actually, you only need to alter the statistics for that particular
column, not for all columns in the db.

What you want to do is:

ALTER TABLE "ClimateChangeModel40"
    ALTER COLUMN <whatever the column is>
    SET STATISTICS 100;
VACUUM ANALYZE "ClimateChangeModel40";

The column is just the column that you have the "IX_ClimateId" index on,
I don't know which one that is.

The statistics value ranges from 1 - 1000, the default being 10, and for
indexed columns you are likely to want somewhere between 100-200.

If you set it to 100 and the planner is still mis-estimating the number
of rows, try 200, etc.

The reason to keep the number low is because with a high number the
planner has to spend more time planning. But especially for queries like
this one, you'd rather the query planner spent a little bit more time
planning, and got the right plan.

John
=:->