On 01.03.2018 22:48, Andres Freund wrote:
> Hi,
>
> I still don't think, as commented upon by Tom and me upthread, that we
> want this feature in the current form.
>
> Your arguments about layering violations seem to be counteracted by the
> fact that ProjectionIsNotChanged() basically appears to do purely
> executor work inside inside heapam.c.
ProjectionIsNotChanged doesn't perform evaluation itslef, is calls FormIndexDatum.
FormIndexDatum is also called in 13 other places in Postgres:
analyze.c, constraint.c, index.c, tuplesort, execIndexing.c
I still think that trying to store somewhere result odf index expression evaluation to be able to reuse in index update
isnot so good idea:
it complicates code and add extra dependencies between different modules.
And benefits of such optimization are not obvious: is index expression evaluation is so expensive, then
recheck_on_updateshould be prohibited for such index at all.
--
Konstantin Knizhnik
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