Re: rows selectivity overestimate for @> operator for arrays

2022-05-27 Thread Tom Lane
Alexey Ermakov writes: > so if we store mostly one element in array and they're almost all > distinct then in tables with more then stats_target/0.0063 (~1.58M for > maximum stats target 1) rows we'll get 0.005 constant for selectivity. Yeah. There's a comment in array_selfuncs.c about *

Re: How to monitor Postgres real memory usage

2022-05-27 Thread Justin Pryzby
On Sat, May 28, 2022 at 01:40:14AM +0800, 徐志宇徐 wrote: > vm.swappiness=0 I think this is related to the problem. swappiness=0 means to *never* use swap, even if that means that processes are killed. If you really wanted that, you should remove the swap space. Swap is extremely slow and worth avo

rows selectivity overestimate for @> operator for arrays

2022-05-27 Thread Alexey Ermakov
Hello, please look into following example: postgres=# create table test_array_selectivity as select array[id]::int[] as a from generate_series(1, 1000) gs(id); SELECT 1000 postgres=# explain analyze select * from test_array_selectivity where a @> array[1];