Jan, I think we should suspend further discussion for now...in summary:
ARC Buffer management is an important new performance feature for 7.5; the implementation is a good one and should have positive benefit for everybody's workload. ARC will adapt to a variety of situations and has been designed to allow Vacuum to avoid interfering with user applications. That's the important bit: The implementation notes are detailed; I've read them a few times to ensure I've got it straight. I am confident that the situation I described CAN exist with regard to multiple concurrent queries performing full table scans upon a single large table. Further debate on that point is continuing because of my poor explanation of that situation; forgive me. Thanks very much for your further explanations and examples. I will take a more practical tack on this now: providing evidence of a real query mix that exhibits the described properties and quantifying the effects and their frequency. If it IS worth it, and I accept that it may not be, I'll have a hack at the very specialised improvement I was suggesting, for very specific workload types. Best Regards Simon Riggs ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org