Обсуждение: dates and partitioning

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?


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?


Thanks in advance...

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.

Tuesday, July 20, 2010, 5:36:07 PM you wrote:


> 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?

Quick guess: How is your 'constraint_exclusion'-setting?
Which version of postgres?

--
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