Piwik with its many small transactions looks like the classical candidate for database connection pooling.
I haven’t been able to find a document way to enable pooling for the connections to our MySQL database.
We ended up modifying function connect() in core/Tracker/Db/Pdo/Mysql.php:
before:
$this->connection = @new PDO($this->dsn, $this->username, $this->password, $config = array(PDO::ATTR_PERSISTENT => true));
after:
$this->connection = @new PDO($this->dsn, $this->username, $this->password, $config = array());
It seems to us that connection pooling should be configurable in config.inc.php.
[This is Piwik 2.4.1]