Uploaded image for project: 'MariaDB Server'
  1. MariaDB Server
  2. MDEV-31095

Create separate tpool thread for async aio

    XMLWordPrintable

Details

    Description

      Linux mutex does not ensure that mutex are given in a FIFO order, but instead allows 'fast threads' to steal the mutex, which causes other threads to starve.

      This is a problem with tpool as if there is burst of aio_reads, it will create 'nproc*2' threads to handle the request even if one thread could do the job (if the block is on a very fast device or on a memory device). If the file is on a hard disk things may be even worse.

      This can be seen by just starting the server on a data directory with a large 'ib_buffer_pool' file.
      In this case the startup code will on my machine create 72 threads on startup to fill the
      buffer pool, which is not a good idea for most system (especially desktops) as the memory
      used may not be released to the operating system.

      In addition the current code does not honor the variables srv_n_read_io_threads or srv_n_write_io_threads.

      The suggested fix is to use a separate tpool for just async io and use a limited number of threads for this. Here is some suggested code to use as a base:

      --- b/storage/innobase/srv/srv0srv.cc
      +++ b/storage/innobase/srv/srv0srv.cc
      @@ -580,12 +580,13 @@ static void thread_pool_thread_end()
       
       void srv_thread_pool_init()
       {
      +  uint max_threads= srv_n_read_io_threads + srv_n_write_io_threads;
         DBUG_ASSERT(!srv_thread_pool);
       
       #if defined (_WIN32)
      -  srv_thread_pool= tpool::create_thread_pool_win();
      +  srv_thread_pool= tpool::create_thread_pool_win(1, max_threads);
       #else
      -  srv_thread_pool= tpool::create_thread_pool_generic();
      +  srv_thread_pool= tpool::create_thread_pool_generic(1, max_threads);
       #endif
         srv_thread_pool->set_thread_callbacks(thread_pool_thread_init,
                                               thread_pool_thread_end);
      

      Attachments

        Issue Links

          Activity

            People

              wlad Vladislav Vaintroub
              monty Michael Widenius
              Votes:
              0 Vote for this issue
              Watchers:
              6 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved:

                Git Integration

                  Error rendering 'com.xiplink.jira.git.jira_git_plugin:git-issue-webpanel'. Please contact your Jira administrators.