8.11.6.1. Thread Pool Components and Installation

The thread pool feature comprises these components:

A plugin library object file contains a plugin for the thread pool code and plugins for several INFORMATION_SCHEMA tables.

For a detailed description of how the thread pool works, see Section 8.11.6.2, "Thread Pool Operation".

The INFORMATION_SCHEMA tables are named TP_THREAD_STATE, TP_THREAD_GROUP_STATE, and TP_THREAD_GROUP_STATS. These tables provide information about thread pool operation. For more information, see Section 20.31, "Thread Pool INFORMATION_SCHEMA Tables".
Several system variables are related to the thread pool. The thread_handling system variable has a value of loaded-dynamically when the server successfully loads the thread pool plugin.

The other related variables are implemented by the thread pool plugin; they are not available unless it is enabled:
- thread_pool_algorithm: The concurrency algorithm to use for scheduling.
- thread_pool_high_priority_connection: How to schedule statement execution for a session.
- thread_pool_prio_kickup_timer: How long before the thread pool moves a statement awaiting execution from the low-priority queue to the high-priority queue.
- thread_pool_max_unused_threads: How many sleeping threads to permit.
- thread_pool_size: The number of thread groups in the thread pool. This is the most important parameter controlling thread pool performance.
- thread_pool_stall_limit: The time before an executing statement is considered to be stalled.
If any variable implemented by the plugin is set to an illegal value at startup, plugin initialization fails and the plugin does not load.

For information about setting thread pool parameters, see Section 8.11.6.3, "Thread Pool Tuning".
The Performance Schema exposes information about the thread pool and may be used to investigate operational performance. For more information, see Chapter 21, MySQL Performance Schema.

To be usable by the server, the thread pool library object file must be located in the MySQL plugin directory (the directory named by the plugin_dir system variable). To enable thread pool capability, load the plugins to be used by starting the server with the --plugin-load option. For example, if you name just the plugin object file, the server loads all plugins that it contains (that is, the thread pool plugin and all the INFORMATION_SCHEMA tables). To do this, put these lines in your my.cnf file:

[mysqld]plugin-load=thread_pool.so

If object files have a suffix different from .so on your system, substitute the correct suffix (for example, .dll on Windows).

If necessary, set the value of the plugin_dir system variable to tell the server the location of the plugin directory.

If desired, you can load individual plugins from the library file. To load the thread pool plugin but not the INFORMATION_SCHEMA tables, use an option like this:

[mysqld]plugin-load=thread_pool=thread_pool.so

To load the thread pool plugin and only the TP_THREAD_STATE INFORMATION_SCHEMA table, use an option like this:

[mysqld]plugin-load=thread_pool=thread_pool.so;TP_THREAD_STATE=thread_pool.so

To verify plugin installation, examine the INFORMATION_SCHEMA.PLUGINS table or use the SHOW PLUGINS statement. See Section 5.1.8.2, "Obtaining Server Plugin Information".

If the server loads the thread plugin successfully, it sets the thread_handling system variable to dynamically-loaded. If the plugin fails to load, the server writes a message to the error log.