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    SubjectRe: [PATCH 00/33] Adaptive read-ahead V12
    On 5/25/06, Andrew Morton <akpm@osdl.org> wrote:
    > These are nice-looking numbers, but one wonders. If optimising readahead
    > makes this much difference to postgresql performance then postgresql should
    > be doing the readahead itself, rather than relying upon the kernel's
    > ability to guess what the application will be doing in the future. Because
    > surely the database can do a better job of that than the kernel.
    >
    > That would involve using posix_fadvise(POSIX_FADV_RANDOM) to disable kernel
    > readahead and then using posix_fadvise(POSIX_FADV_WILLNEED) to launch
    > application-level readahead.

    Users have also reported that this patch fixes performance problems
    from web servers using sendfile(). In the case of lighttpd they
    actually stopped using sendfile() for large transfers and wrote a user
    space replacement where they could control readahead manually. With
    this patch in place sendfile() went back to being faster than the user
    space implementation.

    --
    Jon Smirl
    jonsmirl@gmail.com
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