Re: Combining Aggregates

On Sun, Mar 20, 2016 at 2:23 PM, David Rowley
<david(dot)rowley(at)2ndquadrant(dot)com> wrote:
>
> I've had a look over this. I had to first base it on the 0005 patch,
> as it seemed like the pg_aggregate.h changes didn't include the
> serialfn and deserialfn changes, and an OID was being consumed by
> another function I added in patch 0003.
>
> On testing I also noticed some wrong results, which on investigation,
> are due to the wrong array elements being added together.
>
> For example:
>
> postgres=# select stddev(num) from f;
> stddev
> ------------------
> 28867.5149028984
> (1 row)
>
>
> postgres=# set max_parallel_degree=8;
> SET
> postgres=# select stddev(num) from f;
> stddev
> --------
> 0
> (1 row)
>
> + N += transvalues2[0];
> + sumX += transvalues2[1];
> + CHECKFLOATVAL(sumX, isinf(transvalues1[1]) || isinf(transvalues2[1]), true);
> + sumX2 += transvalues1[2];
>
> The last line should use transvalues2[2], not transvalues1[2].

Thanks.

> There's also quite a few mistakes in float8_regr_combine()
>
> + sumX2 += transvalues2[2];
> + CHECKFLOATVAL(sumX2, isinf(transvalues1[2]) || isinf(transvalues2[1]), true);
>
> Wrong array element on isinf() check
>
> + sumY2 += transvalues2[4];
> + CHECKFLOATVAL(sumY2, isinf(transvalues1[4]) || isinf(transvalues2[3]), true);
>
> Wrong array element on isinf() check
>
> + sumXY += transvalues2[5];
> + CHECKFLOATVAL(sumXY, isinf(transvalues1[5]) || isinf(transvalues2[1]) ||
> + isinf(transvalues2[3]), true);
>
> Wrong array element on isinf() check, and the final
> isinf(transvalues2[3]) check does not need to be there.

Thanks for the changes, I just followed the float8_regr_accum function while
writing float8_regr_combine function. Now I understood isinf proper usage.

Regards,
Hari Babu
Fujitsu Australia