Josh Harrison <joshques@xxxxxxxxx> schrieb: > My questions > 1. I pg_dumped dummy and Shuffled_dummy (from database1) to another database > (database2) > When I issued the query in both database (database1 and database2) > > select * from dummy limit 1000 ( the planner chooses seq scan for this query) > select * from shuffled_dummy limit 1000 (planner chooses seq scan) > > > 2. Also when does the planner switch from choosing index scan to bitmap index > scan? Is it dependent on the number of rows to be retrieved or the position of > the relevant data in the blocks or something else? For a select * ... without a WHERE the db can't use an index, this query forced a seq-scan. A index is used when: - a index are created - a propper WHERE or ORDER BY in the query - this index is useful (a index isn't useful, for instance, for a small table or when almost all rows are in the result set) A bitmap index scan performed when: - 2 or more propper indexes available - see above Andreas -- Really, I'm not out to destroy Microsoft. That will just be a completely unintentional side effect. (Linus Torvalds) "If I was god, I would recompile penguin with --enable-fly." (unknow) Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889° ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
