Re: Avg performance for int8/numeric

This has been saved for the 8.3 release:

    http://momjian.postgresql.org/cgi-bin/pgpatches_hold

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Mark Kirkwood wrote:
> Avg performance for these two datatypes can be improved by *not*
> calculating the sum of squares in the shared accumulator
> (do_numeric_accum). However there is a little subtlety as this function
> is also the shared by variance and stddev!
>
> This patch:
>
> - Modifies do_numeric_accum to have an extra bool parameter and does not
> calc sumX2 when it is false.
> - Amends all the accumulators that call it to include the bool (set to
> true).
> - Adds new functions [int8|numeric]_avg_accum that call do_numeric_accum
> with the bool set to false.
> - Amends the the bootstrap entries for pg_aggregate to use the new
> accumulators for avg(int8|numeric).
> - Adds the new accumulators into the bootstrap entries for pg_proc.
>
> Performance gain is approx 33% (it is still slower than doing sum/count
> - possibly due to the construct/deconstruct overhead of the numeric
> transition array).
>
> Cheers
>
> Mark


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