I hall
I have a query in this form:
empdb=# explain analyze select * from v_past_connections where id_user = 26195 and login_time > '2004-07-21';
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------
IndexScan using idx_user_logs_login_time on user_logs (cost=0.00..14.10 rows=1 width=28) (actual time=66.890..198.998
rows=5loops=1) Index Cond: (login_time > '2004-07-21 00:00:00+02'::timestamp with time zone) Filter: (id_user =
26195)Total runtime: 199.083 ms
(4 rows)
as you see the index on the time stamp column is used
The table have indexes on both columns:
empdb=# explain analyze select * from v_past_connections where login_time > '2004-07-21';
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------
IndexScan using idx_user_logs_login_time on user_logs (cost=0.00..12.90 rows=481 width=28) (actual time=7.338..661.300
rows=22477loops=1) Index Cond: (login_time > '2004-07-21 00:00:00+02'::timestamp with time zone) Total runtime:
676.472ms
(3 rows)
empdb=# explain analyze select * from v_past_connections where id_user = 26195;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------
IndexScan using idx_user_user_logs on user_logs (cost=0.00..252.47 rows=320 width=28) (actual time=4.420..100.122
rows=221loops=1) Index Cond: (id_user = 26195) Total runtime: 100.348 ms
(3 rows)
The rows filtered out with both condictions are two order of magnitude differents,
also the extimated rows are close to real numbers:
empdb=# select count(*) from v_past_connections where id_user = 26195; count
------- 221
(1 row)
empdb=# select count(*) from v_past_connections where login_time > '2004-07-21'; count
------- 22441
(1 row)
why then the planner choose to do an index scan using the filter that retrieve a bigger ammount of rows ? A bug ?
Regards
Gaetano Mendola