Re: [HACKERS] path toward faster partition pruning

On Thu, Sep 28, 2017 at 5:16 AM, David Rowley
<david.rowley@2ndquadrant.com> wrote:
> I'd imagine, for
> each partition key, you'd want to store a Datum with the minimum and
> maximum possible value based on the quals processed. If either the
> minimum or maximum is still set to NULL, then it's unbounded at that
> end. If you encounter partkey = Const, then minimum and maximum can be
> set to the value of that Const. From there you can likely ignore any
> other quals for that partition key, as if the query did contain
> another qual with partkey = SomeOtherConst, then that would have
> become a gating qual during the constant folding process. This way if
> the user had written WHERE partkey >= 1 AND partkey <= 1 the
> evaluation would end up the same as if they'd written WHERE partkey =
> 1 as the minimum and maximum would be the same value in both cases,
> and when those two values are the same then it would mean just one
> theoretical binary search on a partition range to find the correct
> partition instead of two.

I have not looked at the code submitted here in detail yet but I do
think we should try to avoid wasting cycles in the
presumably-quite-common case where equality is being tested.  The
whole idea of thinking of this as minimum/maximum seems like it might
be off precisely for that reason.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


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