As of MySQL 5.5.16, commercial distributions of MySQL include
the thread pool plugin. The default thread-handling model in
MySQL Server executes statements using one thread per client
connection. As more clients connect to the server and execute
statements, overall performance degrades. The thread pool plugin
provides an alternative thread-handling model designed to reduce
overhead and improve performance. The plugin implements a thread
pool that increases server performance by efficiently managing
statement execution threads for large numbers of client
connections.
This is a commercial feature, available as of MySQL 5.5.16. See
Commercial Editions,
http://mysql.com/products/.
The thread pool addresses several problems of the one thread per
connection model:
Too many thread stacks make CPU caches almost useless in
highly parallel execution workloads. The thread pool
promotes thread stack reuse to minimize the CPU cache
footprint.
With too many threads executing in parallel, context
switching overhead is high. This also presents a challenging
task to the operating system scheduler. The thread pool
controls the number of active threads to keep the
parallelism within the MySQL server at a level that it can
handle and that is appropriate for the server host on which
MySQL is executing.
Too many transactions executing in parallel increases
resource contention. In InnoDB,
this increases the time spent holding central mutexes. The
thread pool controls when transactions start to ensure that
not too many execute in parallel.
The thread pool plugin is a commercial feature. It is not
included in MySQL community distributions.
On Windows, the thread pool plugin requires Windows Vista or
newer. On Linux, the plugin requires kernel 2.6.9 or newer.
© 2012, Oracle Corporation and/or its affiliates
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