Re: Partitioning for query performance

On 2010-04-13, Danny Lo <lo.dannyk@gmail.com> wrote:
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> Hi,
>
>
>
> I have a question regarding improving query performing using table
> partitioning:

I recently partitioned a 20Gb table and was amazed at the performance
boost. I only did it because I wanted to delete old data and the original
table was too busy to vacuum.

>                                              EXECUTE 'SELECT * from
> tablename
>
>                                              where date = ''' ||
> current_date || '''';
>
>
....
> A parameterized query will not be optimized, since the
> planner cannot know which partitions the parameter value might select at run
> time. For the same reason, "stable" functions such as CURRENT_DATE must be
> avoided.

(PLPGSQL) EXECUTE is not a parameterised query.

The way you are doing it EXECUTE sees a string with only constants in it.

In any case even without constraint exclusion you can get good (but not best)
perfromance if your parts are indexed on the relevant column; as an
index scan which discovers the requested value is too high or is too low
is very fast (not as fast as constraint exclusion, but still fast)