I've also wondered about the conventional wisdom that read ahead doesn't help random reads. I may well be missing something, but *if* the OS has enough memory to cache most of the table, surely read ahead will still work to your advantage?
Bruno Wolff III wrote:
No. When you are doing an index scan of a significant part of the table,
you will fetch some heap pages more than once. You will also be fetching
blocks out of order, so you will lose out on read ahead optimization
by the OS. This assumes that you don't get a lot of cache hits on the
help pages. If a significant portion of the table is cached, then the
trade off point will be at a higher percentage of the table.
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