On Wed, Oct 28, 2020 at 5:30 PM Tom Lane <t...@sss.pgh.pa.us> wrote: > "Olivier Poquet" <opoq...@plumdev.com> writes: > > Looking at it in more detail, I found that the planner is assuming that > I'll get millions of rows back even when I do a simple query that does an > index scan on my partial index: > > We don't look at partial-index predicates when trying to estimate the > selectivity of a WHERE clause. It's not clear to me whether that'd be > a useful thing to do, or whether it could be shoehorned into the system > easily. (One big problem is that while the index size could provide > an upper bound, it's not apparent how to combine that knowledge with > selectivities of unrelated conditions. Also, it's riskier to extrapolate > a current rowcount estimate from stale relpages/reltuples data for an > index than it is for a table, because the index is less likely to scale > up linearly.) > > regards, tom lane >
Aren't there custom stats created for functional indexes? Would it be feasible to create those for partial indexes as well, maybe only optionally? I assume there may be giant gaps with that notion.
