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
-----------------------------------------------------------------------------------------------------------------------------------------
Index Scan 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=5 loops=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
----------------------------------------------------------------------------------------------------------------------------------------------
Index Scan 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=22477 loops=1)
Index Cond: (login_time > '2004-07-21 00:00:00+02'::timestamp with time zone)
Total runtime: 676.472 ms
(3 rows)empdb=# explain analyze select * from v_past_connections where id_user = 26195;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------
Index Scan using idx_user_user_logs on user_logs (cost=0.00..252.47 rows=320
width=28) (actual time=4.420..100.122 rows=221 loops=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
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