This is one of the big myths about database optimizations. Indexes are not always good, and full table scans are not always bad. I have just experienced this at work. We were able to make 300+% gains on our queries by forcing oracle to do a full table scan over a 12 million row table.

Ultimately, you have to know what your query is doing before you start optimizing it. With Postgres, start using the EXPLAIN syntax to figure out if you're using indexes or full table scans. (ie EXPLAIN select * from foo where baz = 'baz'). Next, it helps to understand what your query is doing, and perhaps create a different index that is more selective.

12 secs to scan a 180k row table sounds awfully slow, but it depends on hardware and your I/O subsystem.


--
Ben
"Naked I came from my mother's womb, and naked I will depart."

In reply to Re^5: Musings about a database ecology by bprew
in thread Musings about a database ecology by talexb

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