2012/6/26 Marc Mamin <M.Mamin@xxxxxxxxxxxx>: > >>> On 22/06/12 09:02, Maxim Boguk wrote: > >>> May be I completely wrong but I always assumed that the access speed to the array element in PostgreSQL should be close to constant time. >>> But in tests I found that access speed degrade as O(N) of array size. > >>> Is that behaviour is correct? yes - access to n position means in postgresql - skip n-1 elements Regards Pavel > > >> From: pgsql-performance-owner@xxxxxxxxxxxxxx On Behalf Of Jesper Krogh > >> Default column storage is to "compress it, and store in TOAST" with large values. >> This it what is causing the shift. Try to change the column storage of the column >> to EXTERNAL instead and rerun the test. > > > Hello, > > I've repeated your test in a simplified form: > you are right :-( > > create table t1 ( _array int[]); > alter table t1 alter _array set storage external; > insert into t1 SELECT ARRAY(SELECT * FROM generate_series(1,50000)); > > create table t2 ( _array int[]); > alter table t2 alter _array set storage external; > insert into t2 SELECT ARRAY(SELECT * FROM generate_series(1,5000000)); > > explain analyze SELECT _array[1] FROM t1; > Total runtime: 0.125 ms > > explain analyze SELECT _array[1] FROM t2; > Total runtime: 8.649 ms > > > best regards, > > Marc Mamin > > > > -- > Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
