"Zeugswetter Andreas ADI SD" <[EMAIL PROTECTED]> writes: >> Are you filling multiple buffers in the buffer cache with a >> single read-call? > > yes, needs vector or ScatterGather IO.
I would expect that to get only moderate improvement. To get the full benefit I would think you would want to either fire off a separate thread to do the read-ahead, use libaio, or funnel the read-ahead requests to a separate thread like our bgwriter only it would be a bgreader or something like that. >> The OS should be doing readahead for us >> anyway, so I don't see how just issuing multiple ReadBuffers >> one after each other helps. > > Last time I looked OS readahead was only comparable to 32k blocked reads. > 256k blocked reads still perform way better. Also when the OS is confronted > with an IO storm the 256k reads perform way better than OS readahead. Well that's going to depend on the OS. Last I checked Linux's readahead logic is pretty straightforward and doesn't try to do any better than 32k readahead and is easily fooled. However I wouldn't be surprised if that's changed. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(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