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    SubjectRe: 2.6.0-test2-mm3 and mysql

    I do not know about the specific corruption Shane is talking about, but I
    could summarize what we have found out in the past 2 years. I have written
    the InnoDB backend to MySQL, and have been hunting Linux corruption bugs for
    2 years now.

    - Corruption seems to happen on Red Hat kernels 2.4.18 under heavy file i/o
    load on some computers.

    - A user ran a very simple stress test of type SELECT 'abbaguu' with many
    clients. On a 2-way Dell server he was able to get mysqld to crash
    predictably in < 24 hours. Sometimes he also got corruption. But another,
    cheaper computer worked ok. Both were running a Red Hat kernel 2.4.18. When
    the user upgraded to a 'stock' kernel 2.4.20, the crashes and corruption

    - Our 4-way Xeon SuSE-2.4.18 computer never corrupts databases, though I run
    very heavy stress tests on it.

    - Kernels 2.4.20 seem to be more reliable than 2.4.18. I have only one
    corruption case from such a kernel.

    - We know with certainty that corruption is sometimes caused by
    OS/drivers/hardware and not by mysqld, because in some cases rebooting the
    computer has magically fixed the corruption. Looks like Linux had corrupted
    its own file cache, but the data on disk was ok. I reported this on the
    Linux kernel mailing list 2 years ago, but got no definite feedback.

    - In some cases InnoDB reports checksum errors in pages. In those cases it
    is also very probable that the corruption was caused by OS/drivers/hardware,
    and not by mysqld.

    - I have not noticed any clear connection between corruption reports and the
    used file system.

    - I have personally tested on 4 Linux computers. On an old 2.2 kernel
    computer I was able to get read errors in 30 seconds. The three 2.4 kernel
    computers have worked ok.

    My hypothesis is that there are bugs in drivers of Linux. That would explain
    why some computers work ok. Or there are Linux kernel bugs which only
    manifest on certain hardware under certain file i/o workload.

    What to do? People who write drivers should run heavy, multithreaded file
    i/o tests on their computer using some SQL database which calls fsync(). For
    example, run the Perl '/sql-bench/innotest's all concurrently on MySQL. If
    the problems are in drivers, that could help.

    Best regards,

    Heikki Tuuri
    Innobase Oy


    List: linux-kernel
    Subject: Re: 2.6.0-test2-mm3 and mysql
    From: Andrew Morton <akpm () osdl ! org>
    Date: 2003-08-03 2:08:59
    [Download message RAW]

    Shane Shrybman <> wrote:
    > The db corruption hit again on test2-mm2.

    How do you know it is "db corruption"?

    > I am still backing out the 64 bit devt bit


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