Hi Tom, You are right, this query is not the right approach for performance testing. I thought that this will give an indication about the performance of a select statement on that table. One of those slow queries are running on col02 which has a btree index. But I use the 'in' expression to get a set of matching rows: select * from table where col02 in ('...',[...],'...') This query gets sometimes really slow, I guess it depends on the size of the set used by 'in'. Would the query perform better when I cluster the index on col02 and force to order the set for the in clause? Is there a way to disable the caching for testing? Once I ran the query, the result set seems to be cached and the second run of the query is fast. This makes a testing a little difficult ;-) regards. Rainer ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to majordomo@xxxxxxxxxxxxxx so that your message can get through to the mailing list cleanly