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  1. MariaDB Server
  2. MDEV-7100

InnoDB error monitor might unnecessary wait log_sys mutex

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          Description

          InnoDB error monitor is responsible to call every second
          sync_arr_wake_threads_if_sema_free() to wake up possible hanging threads if they are missed in mutex_signal_object.

          This is not possible if error monitor itself is on mutex/semaphore wait. We should avoid all unnecessary mutex/semaphore waits on error monitor.

          Currently error monitor calls function buf_flush_stat_update() that calls log_get_lsn() function and there we will try to get log_sys mutex. Better, solution for error monitor is that in buf_flush_stat_update() we will try to get lsn with mutex_nowait() and if we did not get mutex do not update the stats.

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                jplindst Jan Lindström added a comment -

                revno: 4347
                committer: Jan Lindström <jplindst@mariadb.org>
                branch nick: 5.5
                timestamp: Thu 2014-11-13 11:24:19 +0200
                message:
                MDEV-7100: InnoDB error monitor might unnecessary wait log_sys mutex

                Analysis: InnoDB error monitor is responsible to call every second
                sync_arr_wake_threads_if_sema_free() to wake up possible hanging
                threads if they are missed in mutex_signal_object. This is not
                possible if error monitor itself is on mutex/semaphore wait. We
                should avoid all unnecessary mutex/semaphore waits on error monitor.
                Currently error monitor calls function buf_flush_stat_update()
                that calls log_get_lsn() function and there we will try to get
                log_sys mutex. Better, solution for error monitor is that in
                buf_flush_stat_update() we will try to get lsn with
                mutex_enter_nowait() and if we did not get mutex do not update
                the stats.

                Fix: Use log_get_lsn_nowait() function on buf_flush_stat_update()
                function. If returned lsn is 0, we do not update flush stats.
                log_get_lsn_nowait() will use mutex_enter_nowait() and if
                we get mutex we return a correct lsn if not we return 0.

                Show
                jplindst Jan Lindström added a comment - revno: 4347 committer: Jan Lindström <jplindst@mariadb.org> branch nick: 5.5 timestamp: Thu 2014-11-13 11:24:19 +0200 message: MDEV-7100 : InnoDB error monitor might unnecessary wait log_sys mutex Analysis: InnoDB error monitor is responsible to call every second sync_arr_wake_threads_if_sema_free() to wake up possible hanging threads if they are missed in mutex_signal_object. This is not possible if error monitor itself is on mutex/semaphore wait. We should avoid all unnecessary mutex/semaphore waits on error monitor. Currently error monitor calls function buf_flush_stat_update() that calls log_get_lsn() function and there we will try to get log_sys mutex. Better, solution for error monitor is that in buf_flush_stat_update() we will try to get lsn with mutex_enter_nowait() and if we did not get mutex do not update the stats. Fix: Use log_get_lsn_nowait() function on buf_flush_stat_update() function. If returned lsn is 0, we do not update flush stats. log_get_lsn_nowait() will use mutex_enter_nowait() and if we get mutex we return a correct lsn if not we return 0.
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                jplindst Jan Lindström added a comment -

                revno: 4481
                committer: Jan Lindström <jplindst@mariadb.org>
                branch nick: 10.0-bugs
                timestamp: Thu 2014-11-13 12:00:57 +0200
                message:
                MDEV-7100: InnoDB error monitor might unnecessary wait log_sys mutex

                Analysis: InnoDB error monitor is responsible to call every second
                sync_arr_wake_threads_if_sema_free() to wake up possible hanging
                threads if they are missed in mutex_signal_object. This is not
                possible if error monitor itself is on mutex/semaphore wait. We
                should avoid all unnecessary mutex/semaphore waits on error monitor.
                Currently error monitor calls function buf_flush_stat_update()
                that calls log_get_lsn() function and there we will try to get
                log_sys mutex. Better, solution for error monitor is that in
                buf_flush_stat_update() we will try to get lsn with
                mutex_enter_nowait() and if we did not get mutex do not update
                the stats.

                Fix: Use log_get_lsn_nowait() function on buf_flush_stat_update()
                function. If returned lsn is 0, we do not update flush stats.
                log_get_lsn_nowait() will use mutex_enter_nowait() and if
                we get mutex we return a correct lsn if not we return 0.

                Show
                jplindst Jan Lindström added a comment - revno: 4481 committer: Jan Lindström <jplindst@mariadb.org> branch nick: 10.0-bugs timestamp: Thu 2014-11-13 12:00:57 +0200 message: MDEV-7100 : InnoDB error monitor might unnecessary wait log_sys mutex Analysis: InnoDB error monitor is responsible to call every second sync_arr_wake_threads_if_sema_free() to wake up possible hanging threads if they are missed in mutex_signal_object. This is not possible if error monitor itself is on mutex/semaphore wait. We should avoid all unnecessary mutex/semaphore waits on error monitor. Currently error monitor calls function buf_flush_stat_update() that calls log_get_lsn() function and there we will try to get log_sys mutex. Better, solution for error monitor is that in buf_flush_stat_update() we will try to get lsn with mutex_enter_nowait() and if we did not get mutex do not update the stats. Fix: Use log_get_lsn_nowait() function on buf_flush_stat_update() function. If returned lsn is 0, we do not update flush stats. log_get_lsn_nowait() will use mutex_enter_nowait() and if we get mutex we return a correct lsn if not we return 0.

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                  • Assignee:
                    jplindst Jan Lindström
                    Reporter:
                    jplindst Jan Lindström
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