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    SubjectRe: PATCH: Raw device IO for 2.1.131
    Date
      Matthew Brown <mbrown@smartpages.com> writes:
    > Harald Milz writes:
    > > But there _is_ another technical issue nobody mentioned so far in this
    > > thread. Using e.g. Oracle on raw devices saves you from doing a fsck in a
    > > high availability failover situation,
    >
    > Well, you could still use a partition like /dev/sda1 for a database --
    > the only issue is that this goes through the buffer cache instead of
    > reading or writing directly to the disk.
    >
    Wrong. Since the buffer cache makes no guarantee at all about which order
    your data is written, and since you cannot do a partial fsync(), there is
    no integrity guarantee to be had here. (Syncing the whole thing at the end
    of every transaction is obviously out of the question.)

    You could probably open a log file with O_SYNC and trace all changes there,
    but you'd still need some kind of checkpointing.


    All of this, IMHO, just shows that databases are ugly. I mean, look at the
    difference between Oracle and mysql. Oracle is everything including the
    kitchen sink while mysql doesn't even have transactions (just atomic
    updates). A new connection to this here Oracle server takes about a second.
    A complete connect/select-something-simple/disconnect to a mysql server
    on the same machine takes 1/100th of a second. Oracle costs ten times as
    much as mysql (assuming you need to pay for mysql at all, which is not
    always true, and besides it's Open Source).

    Granted that Oracle has tons of features mysql doesn't have, but that
    doesn't exactly justify it being 100 times slower...

    --
    Matthias Urlichs | noris network GmbH | smurf@noris.de | ICQ: 20193661
    The quote was selected randomly. Really. | http://www.noris.de/~smurf/
    --
    My neighbor has a circular driveway.
    He can't get out.
    -- Steve Wright

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