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  1. MariaDB Server
  2. MDEV-329

MariaDB 5.5 does not use fdatasync()

Details

    • Bug
    • Status: Closed (View Workflow)
    • Blocker
    • Resolution: Fixed
    • 5.5.24
    • 5.5.25
    • None
    • None

    Description

      I discovered a serious problem in 5.5 related to fsync (5.3 and below appears
      not affected).

      By default, we do not run any fsync at all. This is because the
      --debug-no-sync option is incorrectly enabled by default.

      This problem was introduced here:

      revid:sergii@pisem.net-20111212225840-8aotf02a1alw1gta

      • {"sync_sys", 0, - "Enable system sync calls. Disable only when running tests or debugging!", - &opt_sync, &opt_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0}

        ,
        +

        {"debug-no-sync", 0, + "Disables system sync calls. Only for running tests or debugging!", + &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0}

        ,

      The option was renamed and the meaning was reversed - but the default was left
      unchanged, effectively reversing the default.

      We need to fix this ASAP, as it causes data loss / silent corruption when the
      host machine crashes.

      There is an additional problem that even with --debug-no-sync=0, we are using
      fsync(), not fdatasync() as we should. There is code to use fdatasync(), but
      apparently availability of fdatasync() is not correctly detected by
      cmake. This is also a quite serious issue; one one machine I tested with a
      good RAID controller, fdatasync() is 2.5 times faster than fsync().

      Work-around: pass --debug-no-sync=0 in config or on command line (but this will not fix fdatasync() performance problem).

      Attachments

        Activity

          This patch seems to fix it:

          === modified file 'config.h.cmake'
          — config.h.cmake 2012-04-19 02:02:28 +0000
          +++ config.h.cmake 2012-06-08 08:49:30 +0000
          @@ -150,6 +150,7 @@
          #cmakedefine HAVE_FCNTL 1
          #cmakedefine HAVE_FCONVERT 1
          #cmakedefine HAVE_FDATASYNC 1
          +#cmakedefine HAVE_DECL_FDATASYNC 1
          #cmakedefine HAVE_FESETROUND 1
          #cmakedefine HAVE_FINITE 1
          #cmakedefine HAVE_FP_EXCEPT 1

          === modified file 'sql/mysqld.cc'
          — sql/mysqld.cc 2012-05-21 18:54:41 +0000
          +++ sql/mysqld.cc 2012-06-08 08:49:06 +0000
          @@ -6161,7 +6161,7 @@ struct my_option my_long_options[]=
          #endif

          {"debug-no-sync", 0, "Disables system sync calls. Only for running tests or debugging!", - &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0}

          ,
          + &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
          #ifdef HAVE_REPLICATION
          {"debug-sporadic-binlog-dump-fail", 0,
          "Option used by mysql-test for debugging and testing of replication.",

          knielsen Kristian Nielsen added a comment - This patch seems to fix it: === modified file 'config.h.cmake' — config.h.cmake 2012-04-19 02:02:28 +0000 +++ config.h.cmake 2012-06-08 08:49:30 +0000 @@ -150,6 +150,7 @@ #cmakedefine HAVE_FCNTL 1 #cmakedefine HAVE_FCONVERT 1 #cmakedefine HAVE_FDATASYNC 1 +#cmakedefine HAVE_DECL_FDATASYNC 1 #cmakedefine HAVE_FESETROUND 1 #cmakedefine HAVE_FINITE 1 #cmakedefine HAVE_FP_EXCEPT 1 === modified file 'sql/mysqld.cc' — sql/mysqld.cc 2012-05-21 18:54:41 +0000 +++ sql/mysqld.cc 2012-06-08 08:49:06 +0000 @@ -6161,7 +6161,7 @@ struct my_option my_long_options[]= #endif {"debug-no-sync", 0, "Disables system sync calls. Only for running tests or debugging!", - &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0} , + &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0}, #ifdef HAVE_REPLICATION {"debug-sporadic-binlog-dump-fail", 0, "Option used by mysql-test for debugging and testing of replication.",

          Pushed to lp:maria/5.5

          knielsen Kristian Nielsen added a comment - Pushed to lp:maria/5.5

          People

            knielsen Kristian Nielsen
            knielsen Kristian Nielsen
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            Dates

              Created:
              Updated:
              Resolved:

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