Threads_created

Compute Thread Cache Miss Rate

The thread cache miss rate can be computed using the Threads_created and Connections status variables:

• The Threads_created status variable shows how many threads have been created since the server was brought online

• The Connections status variable shows how many new connection attempts have been made since the server was brought online

If you divide Threads_created by Connections, that shows the thread cache miss rate:

 SELECT threads_created, connections,
    (threads_created / connections) AS thread_cache_miss_rate
 FROM
    (SELECT gs1.VARIABLE_VALUE AS threads_created
    FROM information_schema.GLOBAL_STATUS gs1
    WHERE gs1.VARIABLE_NAME LIKE 'Threads_created') tc
JOIN
    (SELECT gs2.VARIABLE_VALUE AS connections
    FROM information_schema.GLOBAL_STATUS gs2
    WHERE gs2.VARIABLE_NAME LIKE 'Connections') c;

If the above query is executed at different times, the results can be interpreted in the following way:

• If thread_cache_miss_rate stays constant or grows and approaches 1, the current thread cache size is not large enough to keep up with new connection requests.

• If thread_cache_miss_rate shrinks and approaches 0, the current thread cache size is either equal to or larger than needed to keep up with new connection requests. To determine whether it is larger than needed, the Threads_cached status variable can also be monitored to determine whether the thread cache consistently contains too many cached threads.

For information about how to configure the thread cache, see "thread_cache_size".

Show Value with SHOW STATUS

SHOW GLOBAL STATUS statement can show the global value:

SHOW GLOBAL STATUS
   LIKE 'Threads_created';

Since this status variable is only global scope, SHOW STATUS and SHOW SESSION STATUS also show the global value.

Information Schema

The information_schema.GLOBAL_STATUS table can be queried to obtain the global value:

SELECT *
FROM information_schema.GLOBAL_STATUS
WHERE VARIABLE_NAME LIKE 'Threads_created';

This status variable is only global scope, so the information_schema.SESSION_STATUS table can also be queried to obtain the global value:

SELECT *
FROM information_schema.SESSION_STATUS
WHERE VARIABLE_NAME LIKE 'Threads_created';