On 12/20/2012 12:26 AM, Gavin Flower wrote:
CREATE TABLE test (id int, int sub, text payload);
CREATE INDEX test_idx1 ON test (id, sub);
CREATE INDEX test_idx2 ON test (id);
Now test_idx2 is logically included in test_idx1, but if the majority of transactions only query on id, then test_idx2 would be more better as it ties up less RAM
if sub is an integer, that index isn't that much larger. both indexes need to index all the rows, and with the header and block overhead, the extra word isn't that big of a deal. as long as there are some transactions using the other index, most of both of them will likely want to be in memory, so you'll end up using MORE memory.
