On Fri, Jun 10, 2011 at 1:22 PM, <tv@xxxxxxxx> wrote: >> If I had set the primary key to (diag_id, create_time) would simple >> queries on >> diag_id still work well i.e. >> select * from tdiag where diag_id = 1234; > > Yes. IIRC the performance penalty for using non-leading column of an index > is negligible. But why don't you try that on your own - just run an > explain and you'll get an immediate answer if that works. The effective penalty, which you don't see on your explain, is the size of the index. Depends on the data stored there, but the index can grow up to double size (usually less than that), and the bigger index is slower for all operations. But, in general, if you need both a single-column a multi-column index, just go for a multipurpose multicolumn one. -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
