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  1. 27 Jul, 2007 2 commits
    • malff/marcsql@weblab.(none)'s avatar
      Code review changes · ac7b17ea
      malff/marcsql@weblab.(none) authored
      ac7b17ea
    • malff/marcsql@weblab.(none)'s avatar
      WL#3984 (Revise locking of mysql.general_log and mysql.slow_log) · c7bbd891
      malff/marcsql@weblab.(none) authored
      Bug#25422 (Hang with log tables)
      Bug 17876 (Truncating mysql.slow_log in a SP after using cursor locks the
                thread)
      Bug 23044 (Warnings on flush of a log table)
      Bug 29129 (Resetting general_log while the GLOBAL READ LOCK is set causes
                 a deadlock)
      
      Prior to this fix, the server would hang when performing concurrent
      ALTER TABLE or TRUNCATE TABLE statements against the LOG TABLES,
      which are mysql.general_log and mysql.slow_log.
      
      The root cause traces to the following code:
      in sql_base.cc, open_table()
        if (table->in_use != thd)
        {
          /* wait_for_condition will unlock LOCK_open for us */
          wait_for_condition(thd, &LOCK_open, &COND_refresh);
        }
      The problem with this code is that the current implementation of the
      LOGGER creates 'fake' THD objects, like
      - Log_to_csv_event_handler::general_log_thd
      - Log_to_csv_event_handler::slow_log_thd
      which are not associated to a real thread running in the server,
      so that waiting for these non-existing threads to release table locks
      cause the dead lock.
      
      In general, the design of Log_to_csv_event_handler does not fit into the
      general architecture of the server, so that the concept of general_log_thd
      and slow_log_thd has to be abandoned:
      - this implementation does not work with table locking
      - it will not work with commands like SHOW PROCESSLIST
      - having the log tables always opened does not integrate well with DDL
      operations / FLUSH TABLES / SET GLOBAL READ_ONLY
      
      With this patch, the fundamental design of the LOGGER has been changed to:
      - always open and close a log table when writing a log
      - remove totally the usage of fake THD objects
      - clarify how locking of log tables is implemented in general.
      
      See WL#3984 for details related to the new locking design.
      
      Additional changes (misc bugs exposed and fixed):
      
      1)
      
      mysqldump which would ignore some tables in dump_all_tables_in_db(),
       but forget to ignore the same in dump_all_views_in_db().
      
      2)
      
      mysqldump would also issue an empty "LOCK TABLE" command when all the tables
      to lock are to be ignored (numrows == 0), instead of not issuing the query.
      
      3)
      
      Internal errors handlers could intercept errors but not warnings
      (see sql_error.cc).
      
      4)
      
      Implementing a nested call to open tables, for the performance schema tables,
      exposed an existing bug in remove_table_from_cache(), which would perform:
        in_use->some_tables_deleted=1;
      against another thread, without any consideration about thread locking.
      This call inside remove_table_from_cache() was not required anyway,
      since calling mysql_lock_abort() takes care of aborting -- cleanly -- threads
      that might hold a lock on a table.
      This line (in_use->some_tables_deleted=1) has been removed.
      c7bbd891
  2. 21 Jul, 2007 3 commits
  3. 20 Jul, 2007 6 commits
  4. 19 Jul, 2007 27 commits
  5. 18 Jul, 2007 2 commits