removed in 5.6.1 and works on old Solaris versions < 9
http://www.mysqlperformanceblog.com/2012/06/04/thread_concurrency-doesnt-do-what-you-expect/
#max_heap_table_size=32M
#thread_cache_size=16
#thread_stack=65536
-# Try number of CPU's*2
-#thread_concurrency=8
+# http://www.mysqlperformanceblog.com/2012/06/04/thread_concurrency-doesnt-do-what-you-expect/
+# thread_concurrency is deprecated, removed in 5.6.1 and works on old Solaris versions < 9
#wait_timeout=28800
#query_cache_size=8M
#query_cache_limit=1M