From: | David Johnston <polobo(at)yahoo(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Wrong estimate in query plan |
Date: | 2013-10-24 14:29:51 |
Message-ID: | 1382624991276-5775785.post@n5.nabble.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general |
Eelke Klein wrote
> What I noticed is that are no most common values mentioned ofcourse the
> value 1 only occurs once in the column but as all other values are NULL
> you
> could argue it is a common value.
A random sampling is unlikely to choose a record that only appears in 0.1
percent of the table.
Two sequential scans plus a hash seems like a good plan.
The smaller table is so small a sequential scan is fast. The larger table
experts to have all records read so it to should be scanned. Combining with
a hash seems sound. The fact the cross-column estimate is way off isn't
that big a deal though I'd be curious to hear Tom's opinion on why this is
so for educational purposes.
David J.
--
View this message in context: http://postgresql.1045698.n5.nabble.com/Wrong-estimate-in-query-plan-tp5775727p5775785.html
Sent from the PostgreSQL - general mailing list archive at Nabble.com.
From | Date | Subject | |
---|---|---|---|
Next Message | maillists0 | 2013-10-24 16:10:57 | Re: Replication and fsync |
Previous Message | Rémi Cura | 2013-10-24 14:02:47 | Re: GIST index : order Hack : getting the order used by CLUSTER .. USING my_index |