Fixed BUG#15868: InnoDB hangs under 200 threads making INSERTs: 'thread thrashing'.

 Applied changes due Heikki Tuuri.

sql/mysqld.cc

@@ -5531,7 +5531,7 @@ log and this option does nothing anymore.",
    "Sets the maximum number of threads allowed inside InnoDB. Value 0"
    " will disable the thread throttling.",
    (gptr*) &srv_thread_concurrency, (gptr*) &srv_thread_concurrency,
-   0, GET_LONG, REQUIRED_ARG, 0, 0, 1000, 0, 1, 0},
+   0, GET_LONG, REQUIRED_ARG, 8, 0, 1000, 0, 1, 0},
   {"innodb_thread_sleep_delay", OPT_INNODB_THREAD_SLEEP_DELAY,
    "Time of innodb thread sleeping before joining InnoDB queue (usec). Value 0"
     " disable a sleep",