Subject: Re: dates and partitioning
From: Brad Nicholson <bnichols@ca.afilias.info>
To: Kevin Kempter <cs_dba@consistentstate.com>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <201007200936.07736.cs_dba@consistentstate.com>
References: <201007200936.07736.cs_dba@consistentstate.com>
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Date: Tue, 20 Jul 2010 11:55:30 -0400
Message-ID: <1279641330.15825.91.camel@bnicholson-desktop>
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On Tue, 2010-07-20 at 09:36 -0600, Kevin Kempter wrote:
> Hi All;
> 
> we have a table partitioned by day, the check constraint on the child tables 
> looks like this (this is the may 31st partition):
> 
> CHECK 
> (stime >= '2010-05-30 00:00:00+00'::timestamp with time zone 
>   AND stime <= '2010-05-30 23:59:59+00'::timestamp with time zone)
> 
> 
> We have a python based app that creates code like this:
> 
>                 select
>                  *
>                 from
>                     table_a a, 
>                     table_b b,
>                     table_d d
>                 where a.id = b.id
>                     and b.id = d.id
>                     and stime >= timestamp %s at time zone \'UTC\'
>                     and stime < timestamp %s at time zone \'UTC\'
>                     and stime >= timestamp %s at time zone d.name
>                     and stime < timestamp %s at time zone d.name
>                    ...
> 
> 
> so here's my questions:
> 
> 1) the above app generated query pshows up like this in pg_stat_activity:
> 
> and stime >= timestamp E'2010-07-17' at time zone 'UTC'   
> and stime < timestamp E'2010-07-21' at time zone 'UTC' 
> and stime >= timestamp E'2010-07-18' at time zone d.name  
> and stime < timestamp E'2010-07-19' at time zone d.name 
> 
> what's the E'date' from? and why does it show up this way?

That's E is an escape character.  Python is likely putting that in.

See http://www.postgresql.org/docs/8.4/static/sql-syntax-lexical.html -
section 4.1.2.2

> 
> 2) the above query creates a plan that does a sequential scan & filter on 
> every partition. Why won't it only hit the correct partitions? Is it due to 
> the way the date was specified? or maybe the "at time zone" syntax?

Do you have constraint_exclusion turned on?

-- 
Brad Nicholson  416-673-4106
Database Administrator, Afilias Canada Corp.