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  1. MariaDB Server
  2. MDEV-7340

[PATCH] parallel replication status variables

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    Description

      from pivanof on mailing list in reference to parallel replication:

      > some status variables which could be plotted over time and show (or at
      > least hint on) whether this is significant bottleneck for performance
      > or not.

      > This could be something like total time (in both wall time and
      > accumulated CPU time) spent executing transactions in parallel, time
      > spent rolling back transactions due to this lock conflict, time spent
      > rolling back transactions because of other reasons (e.g. due to STOP
      > SLAVE or reconnect after master crash), maybe also time spent waiting
      > in one parallel thread while transaction is executing in another
      > thread, etc.

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          Task - A task that needs to be done. MDEV-7202 [PATCH] additional statistics for parallel replication - Slave_parallel_eventqueue_size/Slave_parallel_eventqueue_freepending

          • Minor - Minor loss of function, or other problem where easy workaround is present.
          • Closed
          relates to

          Task - A task that needs to be done. MDEV-5296 No status information available for parallel replication

          • Major - Major loss of function.
          • Open

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            danblack Daniel Black added a comment -

            nice. Thank you. Was looking to see if anything other than status_lock could be used but like you didn't see an easy approach. status vars look good.

            danblack Daniel Black added a comment - nice. Thank you. Was looking to see if anything other than status_lock could be used but like you didn't see an easy approach. status vars look good.
            knielsen Kristian Nielsen added a comment - - edited

            Do you mean LOCK_status?

              statistic_add(*current_status_var,
            		 
                            new_time - slave_worker_phase_start_time, &LOCK_status);

            If my understanding is correct, this statistic_add compiles into an atomic
            add operation on platforms of interest. The lock is not actually used,
            unless some wierd platform that does not have atomic operations.

            EDIT: Actually, it appears that neither lock nor atomic operations are
            used. There is a SAFE_STATISTICS define that causes them to be used, but it
            is never enabled. So there is no locking apparently, and the statistics can
            at least theoretically be off, trading 100% accuracy for improved
            performance.

            knielsen Kristian Nielsen added a comment - - edited Do you mean LOCK_status? statistic_add(*current_status_var, new_time - slave_worker_phase_start_time, &LOCK_status); If my understanding is correct, this statistic_add compiles into an atomic add operation on platforms of interest. The lock is not actually used, unless some wierd platform that does not have atomic operations. EDIT: Actually, it appears that neither lock nor atomic operations are used. There is a SAFE_STATISTICS define that causes them to be used, but it is never enabled. So there is no locking apparently, and the statistics can at least theoretically be off, trading 100% accuracy for improved performance.
            danblack Daniel Black added a comment -

            thanks for looking this up.

            I'm quite happy with this tradeoff.

            If you're happy with its final form any chance of a backport? It applies to 10.0 with minimal fuzz.

            danblack Daniel Black added a comment - thanks for looking this up. I'm quite happy with this tradeoff. If you're happy with its final form any chance of a backport? It applies to 10.0 with minimal fuzz.
            danblack Daniel Black added a comment -

            Any chance of a port to 10.0? I don't particularly care if it changes sightly in the future. Something is better than nothing.

            danblack Daniel Black added a comment - Any chance of a port to 10.0? I don't particularly care if it changes sightly in the future. Something is better than nothing.
            danblack Daniel Black added a comment -

            Amazingly this patch still applies (with fuzz level 3) to 10.1 head. I didn't test the current correctness however.

            danblack Daniel Black added a comment - Amazingly this patch still applies (with fuzz level 3) to 10.1 head. I didn't test the current correctness however.

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              knielsen Kristian Nielsen
              danblack Daniel Black
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