On Thu, Aug 12, 2021 at 09:38:45AM -0400, Matt Dupree wrote: > > The rowcount estimate for the time column is bad for all these plans - do you > > know why ? You're using inheritence - have you analyzed the parent tables recently ? > > Yes. I used ANALYZE before posting, as it's one of the "things to try" > listed in the slow queries wiki. I even ran the queries immediately after > analyzing. No difference. Can you say more about why the bad row estimate > would cause Postgres to use the bigger index? I would expect Postgres to > use the smaller index if it's over-estimating how many rows will be > returned. The overestimate is in the table's "time" column (not index) and applies to all the plans. Is either half of the AND estimated correctly? If you do a query with only ">=", and a query with only "<=", do either of them give an accurate rowcount estimate ? |Index Scan using other_events_1004175222_pim_evdef_67951aef14bc_idx on public.other_events_1004175222 (cost=0.28..1,648,877.92 rows=1,858,891 width=32) (actual time=1.008..15.245 rows=23 loops=1) |Index Cond: ((other_events_1004175222."time" >= '1624777200000'::bigint) AND (other_events_1004175222."time" <= '1627369200000'::bigint)) It seems like postgres expects the scan to return a large number of matching rows, so tries to use the more selective index which includes the "type" column. But "type" is not very selective either (it has only 4 distinct values), and "time" is not the first column, so it reads a large fraction of the table, slowly. Could you check pg_stat_all_tables and be sure the last_analyzed is recent for both parent and child tables ? Could you send the histogram bounds for "time" ? SELECT tablename, attname, inherited, array_length(histogram_bounds,1), (histogram_bounds::text::text[])[1], (histogram_bounds::text::text[])[array_length(histogram_bounds,1)] FROM pg_stats ... ; -- Justin
