Sharing connections

The PHP mysqlnd connection multiplexing plugin
changes the relationship between a users connection handle and the
underlying MySQL connection. Without the plugin, every MySQL
connection belongs to exactly one user connection at a time. The
multiplexing plugin changes. A MySQL connection is shared among
multiple user handles. There no one-to-one relation if using the
plugin.

Sharing pooled connections has an impact on the
connection state. State changing operations from multiple user
handles pointing to one MySQL connection are not isolated from each
other. If, for example, a session variable is set through one user
connection handle, the session variable becomes visible to all
other user handles that reference the same underlying MySQL
connection.

This is similar in concept to connection state
related phenomens described for the PHP mysqlnd replication and
load balancing plugin. Please, check the PECL/mysqlnd_ms
documentation for more details on the state of a
connection.

The proof-of-concept takes no measures to isolate
multiplexed connections from each other.