On Wed, May 24, 2017 at 2:17 PM, Justin Pryzby <pry...@telsasoft.com> wrote:
> We got bitten again by what appears to be the same issue I reported > (perhaps > poorly) here: > https://www.postgresql.org/message-id/20170326193344. > GS31628%40telsasoft.com > > We have PG9.6.3 table heirarchies partitioned by time. Our reports use > subqueries each with their own copies of a range clauses on time column, as > needed to get constraint exclusion reference: > https://www.postgresql.org/message-id/25076.1366321335%40sss.pgh.pa.us > > SELECT * FROM > (SELECT * FROM t WHERE col>const) a JOIN > (SELECT * FROM t WHERE col>const) b USING (col) > > I'm diagnosing a bad estimate/plan due to excessively high n_distinct > leading > to underestimated rowcount when selecting from a small fraction of the > table > heirarchy. This leads intermittently to bad things, specifically a > cascade of > misestimates and associated nested loops around millions of rows. > ​Justin, I'm not going to be much help personally but I just wanted to say that with PGCon just completed and Beta1 just starting, combined with the somewhat specialized nature of the problem, a response should be forthcoming even though its taking a bit longer than usual. David J.
