"Jim C. Nasby" <[EMAIL PROTECTED]> writes: > Before we start debating merits of proposals based on random reads, can > someone confirm that the sampling code actually does read randomly?
Well, it's not so much that it's not "random", as that it's not sequential --- it skips blocks, and therefore you'd expect that kernel-level read-ahead would not kick in, or at least not be very effective. If there weren't much else going on, you could still assume that you'd be paying less seek cost than in a genuinely random-order fetching of the same number of blocks. Not sure how these effects would add up. I agree that some investigation would be wise before making any claims about how expensive the current method actually is. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly