Julien Rouhaud <julien.rouh...@dalibo.com> writes:
> I figured out that it's not possible to use a hypothetical gin index, as
> the gincostestimate function try to retrieve some statistical data from
> the index meta page.
> Attached patch fixes this. I believe this should be back-patched as was
I don't much care for this patch though. The core problem is that just
returning all zeroes seems quite useless: it will probably result in silly
cost estimates. The comment in the patch claiming that this would be the
situation in a never-vacuumed index is wrong, because ginbuild() updates
those stats too. But I'm not sure exactly what to do instead :-(.
Ideally we'd put it on the head of the hypothetical-index plugin to invent
some numbers, but I dunno if we want to create such an API or not ... and
we certainly couldn't back-patch such a change.
Maybe we could do something along the lines of pretending that 90% of the
index size given by the plugin is entry pages? Don't know what a good
ratio would be exactly, but we could probably come up with one with a bit
regards, tom lane
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