On 10/18/14, 5:46 PM, Tom Lane wrote:
Marko Tiikkaja <ma...@joh.to> writes:
Yes, exactly; if I had had the option to disable the index from the
optimizer's point of view, I'd have seen that it's not used for looking
up any data by any queries, and thus I would have known that I can
safely drop it without slowing down queries. Which was the only thing I
cared about, and where the stats we provide failed me.
This argument is *utterly* wrongheaded, because it assumes that the
planner's use of the index provided no benefit to your queries. If the
planner was touching the index at all then it was planning queries in
which knowledge of the extremal value was relevant to accurate selectivity
estimation. So it's quite likely that without the index you'd have gotten
different and inferior plans, whether or not those plans actually chose to
use the index.
Maybe. But at the same time that's a big problem: there's no way of
knowing whether the index is actually useful or not when it's used only
by the query planner.
.marko
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