Re: PG planning randomly ?

On Tue, Feb 26, 2008 at 11:12 AM, Laurent Raufaste <analogue@glop.org> wrote:
> 2008/2/26, Tom Lane <tgl@sss.pgh.pa.us>:
>
> >
>  > What PG version is this?
>  >
>  >  If it's 8.2 or later then increasing the stats target for _comment.path
>  >  to 100 or more would likely help.
>  >
>
>  I'm using PG 8.2.4.
>  We are using 100 as default_statistics_target by default and all our
>  column are using this value:
>  # SELECT attname,attstattarget FROM pg_attribute WHERE attrelid=16743
>  AND attname='path' ;
>   attname | attstattarget
>  ---------+---------------
>   path    |            -1
>
>  I tried increasing the stats target with the command:
>  SET default_statistics_target=1000 ;
>  That's the command I launched before executing the ANALYZE showed in
>  the previous mail.
>  The ANALYZE were longer to complete, but it did not change the planner
>  behavior (sometimes right, sometimes wrong).

You're doing it wrong.  The default target affects newly created
columns / tables.  You need to use alter table to change a stats
target after creation.  Like so:

alter table abc alter column xyz set statistics 100;