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    SubjectRe: [PATCHSET v5 0/12] Add support for async buffered reads
    Hi,

    On 2020-06-05 16:56:44 -0600, Jens Axboe wrote:
    > On 6/5/20 4:54 PM, Andres Freund wrote:
    > > On 2020-06-05 16:49:24 -0600, Jens Axboe wrote:
    > >> Yes that's expected, if we have to fallback to ->readpage(), then it'll
    > >> go to a worker. read-ahead is what drives the async nature of it, as we
    > >> issue the range (plus more, depending on RA window) as read-ahead for
    > >> the normal read, then wait for it.
    > >
    > > But I assume async would still work for files with POSIX_FADV_RANDOM
    > > set, or not? Assuming the system wide setting isn't zero, of course.
    >
    > Yes it'll work if FADV_RANDOM is set.

    Cool.


    > But just not if read-ahead is totally disabled. I guess we could make
    > that work too, though not sure that it's super important.

    It's not from my end. I was just trying to check if the reduced
    performance I saw was related to interactions between PG prefetching and
    kernel level prefetching. And changing the /sys entry seemed easier than
    making postgres set POSIX_FADV_RANDOM...

    Greetings,

    Andres Freund

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