位图索引的一些特性?
位图索引的优缺点?
来看下位图扫描的例子。
query plan ------------------------------------------------------------------------------------------------------------------------- ------------------- bitmap heap scan on bitmap_test (cost=2023.16..4157.75 rows=99967 width=4) (actual time=24.373..41.054 rows=100000 loop s=1) recheck cond: (is_visible = 'yes'::bpchar) -> bitmap index scan on idx_bitmap_is_visible (cost=0.00..1998.17 rows=99967 width=0) (actual time=24.252..24.252 ro ws=100000 loops=1) index cond: (is_visible = 'yes'::bpchar) total runtime: 47.175 ms (5 rows) time: 47.725 ms