> -----Original Message----- > From: Pavel Stehule [mailto:pavel.stehule@xxxxxxxxx] > > 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 Hmmm... how many elements to be skipped here ? SELECT _array[1] FROM t2; I wonder if the time rather get spent in first retrieving the array itself before accessing its elements. regards, Marc Mamin > > 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
