Hi, i think i need a little help with a problem with pg_statistic. Lets say i have a table to collect traffic-data. The table has a column time_stamp of type timesamptz. The table has a single-column index on time_stamp. The table has around 5 million records.
If i delete all statistical data from pg_statistic and do a explain analyze i got this result. ------------------------------------------------------------------------- explain analyze select * from tbl_traffic where tbl_traffic.time_stamp >= '2003-05-01' and tbl_traffic.time_stamp < '2003-06-01'; NOTICE: QUERY PLAN: Index Scan using idx_ts on tbl_traffic (cost=0.00..97005.57 rows=24586 width=72) (actual time=0.19..7532.63 rows=1231474 loops=1) Total runtime: 8179.08 msec EXPLAIN ------------------------------------------------------------------------- after i do a vacuum full verbose analyze i got the following result. ------------------------------------------------------------------------- explain analyze select * from tbl_traffic where tbl_traffic.time_stamp >= '2003-05-01' and tbl_traffic.time_stamp < '2003-06-01'; NOTICE: QUERY PLAN: Seq Scan on tbl_traffic (cost=0.00..127224.24 rows=1197331 width=52) (actual time=0.03..14934.70 rows=1231474 loops=1) Total runtime: 15548.35 msec EXPLAIN ------------------------------------------------------------------------- now i disable seqscans with set enable_seqscan to off and i got the following. ------------------------------------------------------------------------- explain analyze select * from tbl_traffic where tbl_traffic.time_stamp >= '2003-05-01' and tbl_traffic.time_stamp < '2003-06-01'; NOTICE: QUERY PLAN: Index Scan using idx_ts on tbl_traffic (cost=0.00..3340294.11 rows=1197331 width=52) (actual time=0.21..7646.29 rows=1231474 loops=1) Total runtime: 8285.92 msec EXPLAIN ------------------------------------------------------------------------- Could anybody explain or give some hint why the index is not used although it is faster than a sequence-scan ? BTW: version ----------------------------------------------------------- PostgreSQL 7.2 on i686-pc-linux-gnu, compiled by GCC 2.96 Thanks in advance, as ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org