On Sun, Jun 23, 2019 at 10:23:19PM +0200, Tomas Vondra wrote:
On Sun, Jun 23, 2019 at 08:48:26PM +0100, Dean Rasheed wrote:
On Sat, 22 Jun 2019 at 15:10, Tomas Vondra <tomas.von...@2ndquadrant.com> wrote:
One annoying thing I noticed is that the base_frequency tends to end up
being 0, most likely due to getting too small. It's a bit strange, though,
because with statistic target set to 10k the smallest frequency for a
single column is 1/3e6, so for 2 columns it'd be ~1/9e12 (which I think is
something the float8 can represent).
Yeah, it should be impossible for the base frequency to underflow to
0. However, it looks like the problem is with mcv_list_items()'s use
of %f to convert to text, which is pretty ugly.
Yeah, I realized that too, eventually. One way to fix that would be
adding %.15f to the sprintf() call, but that just adds ugliness. It's
probably time to rewrite the function to build the tuple from datums,
instead of relying on BuildTupleFromCStrings.
OK, attached is a patch doing this. It's pretty simple, and it does
resolve the issue with frequency precision.
There's one issue with the signature, though - currently the function
returns null flags as bool array, but values are returned as simple
text value (formatted in array-like way, but still just a text).
In the attached patch I've reworked both to proper arrays, but obviously
that'd require a CATVERSION bump - and there's not much apetite for that
past beta2, I suppose. So I'll just undo this bit.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
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