969 Server Status Variables The number of times that a request for a table lock could not be granted immediately and a wait was needed. If this is high and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication. The number of hits for open tables cache lookups. The number of misses for open tables cache lookups. The number of overflows for the open tables cache. This is the number of times, after a table is opened or closed, a cache instance has an unused entry and the size of the instance is larger than table_open_cache  /  table_open_cache_instances . For the memory-mapped implementation of the log that is used by  mysqld  when it acts as the transaction coordinator for recovery of internal XA transactions, this variable indicates the largest number of pages used for the log since the server started. If the product of  Tc_log_max_pages_used and  Tc_log_page_size  is always significantly less than the log size, the size is larger than necessary and can be reduced. (The size is set by the  --log-tc-size  option. This variable is unused: It is unneeded for binary log-based recovery, and the memory-mapped recovery log method is not used unless the number of storage engines that are capable of two-phase commit and that support XA transactions is greater than one. ( InnoDB  is the only applicable engine.) The page size used for the memory-mapped implementation of the XA recovery log. The default value is determined using  getpagesize() . This variable is unused for the same reasons as described for Tc_log_max_pages_used . For the memory-mapped implementation of the recovery log, this variable increments each time the server was not able to commit a transaction and had to wait for a free page in the log. If this value is large, you might want to increase the log size (with the  --log-tc-size  option). For binary log-based recovery, this variable increments each time the binary log cannot be closed because there are two- phase commits in progress. (The close operation waits until all such transactions are finished.) The number of threads in the thread cache. The number of currently open connections. The number of threads created to handle connections. If  Threads_created  is big, you may want to increase the  thread_cache_size  value. The cache miss rate can be calculated as Threads_created / Connections . • Threads_created • Threads_connected • Threads_cached • Tc_log_page_waits • Tc_log_page_size • Tc_log_max_pages_used • Table_open_cache_overflows • Table_open_cache_misses • Table_open_cache_hits • Table_locks_waited