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Oracle Enterprise Manager for MySQL Database User's Guide
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6.40 Threads Activity Metrics

Lists the Threads Activity metrics and provides a brief description of each.

Table 6.40 Threads Activity Metrics

CachedThe number of threads in the thread cache.
ConnectedThe number of currently open connections.
Created (Delta)The number of threads created to handle connections.
RunningThe number of threads that are not sleeping.
Slow Launch Threads (Delta)The number of threads that have taken more than slow_launch_time seconds to create.
Connection Limit Usage (Rate)Once the maximum connection limit for the MySQL server has been reached, no other user connections can be established and errors occur on the client side of the application.
Thread Pooling Not EnabledAs of MySQL 5.5.16, commercial distributions of MySQL include a thread pool plugin that provides an alternative thread-handling model designed to reduce overhead and improve performance. It implements a thread pool that increases server performance by efficiently managing statement execution threads for large numbers of client connections. With servers that have many concurrent active connections (generally, more than the number of CPUs within the machine) it can be beneficial for performance to enable the Thread Pool plugin. This keeps the number of actively executing threads within the server lower, generally leaving less contention for locks and resources, whilst still maintaining very high connection counts from applications.
Too Many Concurrent Queries RunningToo many active queries indicates there is a severe load on the server, and may be a sign of lock contention or unoptimized SQL queries.