Re: Help on query plan.

> What does pg_stats show as the correlation value for the ip column?
> If you increase the statistics target and re-ANALYZE, does the
> correlation value change?
>
> regards, tom lane

well well well...let me see...I'm digging into an obscure
world...sorry I've never used a real database, just mysql heehe.

OK, as I don't know what is much and what isn't for the stats target,
I tried to increase it firstly to 15 (10 is default according to
documentation) and then to 20. Results follow:

No changes at all. Normal values since db build.
------------------------------------------------
access=# select correlation,attname from pg_stats where attname='ip';
correlation | attname
-------------+---------
0.202063 | ip
(1 row)

Changing statistics target to 15
------------------------------------------------
access=# alter table tbl_access alter column ip set statistics 15;
ALTER TABLE
access=# analyze verbose tbl_access (ip);
INFO: Analyzing public.tbl_access
ANALYZE
access=# select correlation,attname from pg_stats where attname='ip';
correlation | attname
-------------+---------
0.25932 | ip
(1 row)

Changing statistics target to 20
------------------------------------------------
access=# alter table tbl_access alter column ip set statistics 20;
ALTER TABLE
access=# analyze verbose tbl_access (ip);
INFO: Analyzing public.tbl_access
ANALYZE
access=# select correlation,attname from pg_stats where attname='ip';
correlation | attname
-------------+---------
0.213223 | ip
(1 row)

---------------------------------------------------------

Is there any place I can find more about how to better analyze the
data postgresql offers me? It looks really helpfull...

Thanks,

william

--
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