Heikki Linnakangas wrote: > > Should we consider only telling the kernel X pages ahead, meaning when > > we are on page 10 we tell it about page 16? > > Yes. You don't want to fire off thousands of posix_fadvise calls > upfront. That'll just flood the kernel, and it will most likely ignore > any advise after the first few hundred or so. I'm not sure what the > appropriate amount of read ahead would be, though. Probably depends a > lot on the OS and hardware, and needs to be a adjustable. > > In some cases we can't easily read ahead more than a certain number of > pages. For example, in a regular index scan, we can easily fire off > posix_advise calls for all the heap pages referenced by a single index > page, but reading ahead more than that becomes much more complex.
And if you read-ahead too far the pages might get pushed out of the kernel cache before you ask to read them. -- Bruce Momjian <[EMAIL PROTECTED]> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
