whoops, didn't see the i=9 (linebreak! linebreak!)
nonetheless that is a static constant constraint on the column i, and i was asking if constraint exclusions would work
fordynamic constraints (like those derived from a table joined against.) so for example the bar table has only 0-9 in
itshistogram for i, but constraint exclusion can't use that to eliminate tables foo_2 and foo_3. this is precisely the
kindof information an index can use via join selectivity.
i am not going to the pg conference, sorry to say.
b
On Oct 28, 2010, at 1:48 PM, Joshua D. Drake wrote:
> On Thu, 2010-10-28 at 12:59 -0700, Ben wrote:
>> On Oct 28, 2010, at 12:44 PM, Joshua D. Drake wrote:
>>>
>>> My tests show you are incorrect:
>>>
>>>
>>> part_test=# explain analyze select * from foo join bar using (i) where
>>> i=9;
>>> QUERY
>>> PLAN
>>> ------------------------------------------------------------------------------------------------------------------
>>> Nested Loop (cost=34.26..106.76 rows=200 width=20) (actual
>>> time=0.004..0.004 rows=0 loops=1)
>>> -> Append (cost=0.00..68.50 rows=20 width=12) (actual
>>> time=0.004..0.004 rows=0 loops=1)
>>> -> Seq Scan on foo (cost=0.00..34.25 rows=10 width=12)
>>> (actual time=0.001..0.001 rows=0 loops=1)
>>> Filter: (i = 9)
>>> -> Seq Scan on foo_1 foo (cost=0.00..34.25 rows=10 width=12)
>>> (actual time=0.000..0.000 rows=0 loops=1)
>>> Filter: (i = 9)
>>> -> Materialize (cost=34.26..34.36 rows=10 width=12) (never
>>> executed)
>>> -> Seq Scan on bar (cost=0.00..34.25 rows=10 width=12) (never
>>> executed)
>>> Filter: (i = 9)
>>> Total runtime: 0.032 ms
>>> (10 rows)
>>
>> strange. my tests don't agree with your tests :
>
> Do you have constraint_exclusion turned on? You should verify with show
> constraint_exclusion (I saw what you wrote below).
>
> JD
>
> P.S. Blatant plug, you coming to http://www.postgresqlconference.org ?
>
>
> --
> PostgreSQL.org Major Contributor
> Command Prompt, Inc: http://www.commandprompt.com/ - 509.416.6579
> Consulting, Training, Support, Custom Development, Engineering
> http://twitter.com/cmdpromptinc | http://identi.ca/commandprompt
>