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    SubjectRe: [PATCH] O_STREAMING - flag for optimal streaming I/O

    On 09-Oct-2002 Andrew Morton wrote:
    > Giuliano Pochini wrote:
    >>
    >> > The point of O_STREAMING is one change: drop pages in the pagecache
    >> > behind our current position, that are free-able, because we know we will
    >> > never want them.
    >>
    >> Does it drop pages unconditionally ?
    >
    > Yup.
    >
    >> What happens if I do a
    >> streaming_cat largedatabase > /dev/null while other processes
    >> are working on it ?
    >
    > You'll make your database run really slowly.
    >
    >> It's not a good thing to remove the whole
    >> cached data other apps are working on.
    >
    > Don't do that then ;)

    I was thinking about hot backups of databases. But even if it
    did not drop caches "shared" by other processes it would drop
    them anyway because write-behind is still on. Probably only
    O_DIRECT can help in this case.

    > Seriously, there are tons of ways of creating local performance
    > DoS'es of this form. fsync is an excellent tool for that.

    Yes, I'm aware of that.


    Bye.

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