PowerPoint-Prsentation

Ulf Wendel, Oracle

PECL/mysqlnd_mux 1.0.0-prototype

PHP mysqlnd
Connection Multiplexing

The speaker says...

When fast is not fast enough, you pull all triggers. This includes attempts to optimize an already reasonable fast operation: connect time to MySQL.

The PHP mysqlnd connection multiplexing plugin, shares a physical connection among multiple user handles. Thus, connection overhead is saved on the client side and the number of opened connection is reduced on the server side.PECL/mysqlnd_mux is an Oracle open source development available from pecl.php.net. Developed by Andrey Hristov.

Plugins are mostly transparent

WordPress, Drupal, Symfony, Oxid, ZendFramework, ...mysql, mysqli, PDO_MYSQLmysqlndConnection MultiplexingPECL/mysqlnd_mux plugin

MySQL Server

The speaker says...

PECL/mysqlnd_mux is a plugin for the mysqlnd library. The mysqlnd library is the default C client library used by the PHP MySQL extensions mysql, mysqli and PDO_MySQL internally. Mysqlnd ships with PHP since 5.3.

Plugins operate at a layer beneath the user APIs, thus improvements are available to all PHP MySQL APIs.

Other free plugins are PECL/mysqlnd_ms (replication and load balancing), PECL/mysqlnd_qc (client-side query cache) and many more.

Multiplexing: share connection among handles

Reduce client connect overhead, reduce server load

Prototype, requires PHP 5.5.0+

PECL/mysqlnd_mux

connect()MySQLPECL/mysqlnd_muxconnect()connect()

1 connectionn connection handles

The speaker says...

The PHP mysqlnd connection multiplexing proxies MySQL connections. Whenever a client attempts to open a connection to a host, the plugin checks whether there is already a cached network connection to the host in question. If not, a new connection is established and associated with the users' connection handle. Otherwise, the users' connection handle is linked with an already opened network connection.

This way, multiple user handles can point to the same network connection and share it. Connection overhead is saved and fewer connections are opened.

Multiplexing means serializing tasks

Possibility of wait situations

Prototype: no upgrade to dedicated connection

Prototype: no collision counter

The price you pay

MySQLMUXQuery 1Query 2

Query 1Query 2

Time

The speaker says...

Sharing a resource often requires serializing access to it. This is also the case with a shared connection of the PHP mysqlnd connection multiplexing plugin. Serializing actions bares the risks of collisions and wait situations. In the example, a clients query has to wait for completion of another clients query before it can be executed. Query 2 waits for query 1 to finish.

The prototype is using a mutex to synchronize access to a shared connection.

No new API calls, it just works!

Supports popular buffered queries
(mysql_query(), mysqli_query(),
PDO if using PDO::ATTR_EMULATE_PREPARES)

Prototype does not handle unbuffered queries
(mysqli_real_query())

Prepared statements not in 1.0.0-prototype
(mysqli_stmt_*())

MUX as a demo of the plugin API

The speaker says...

PECL/mysqlnd_mux 1.0.0-prototype is an example of the strenghts of the mysqlnd C plugin API. The initial public release is not a production-ready stable solution. Features have been skipped for the prototype to keep the demo of the plugin API short and comprehensive.

The astonishing finding of the plugin is that multiplexing can be added to add PHP MySQL APIs without changing the APIs. It just works for some cases already today. Other cases could be covered in future versions, depending on user feedback.

THAT'S IT FOLKS?

Connection remains open after close()

Connection establishment overhead reduced

Number of concurrent connections not reduced

Usually, connection state reset upon reuse

Compared to pooling

ClientMySQLConnection poolClient

ConnectionConnectionConnection

The speaker says...

A connection pool is a cache for connections. If a client openes a connection, the pool is checked for an already estiablished connection to the requested host. In case of a hit, the pooled connection is reset, then taken from the pool of unused connections and returned to the client. If no connection is found a new one gets opened and returned to the caller. Then, the connection is used until the client calls close(). Upon close(), the connection is not closed but put back into the pool for reuse.

Pooling saves time on reuse but does not reduce the total number of concurrent connections.

Connection remains open after close()

Connection overhead and reuse costs reduced

Number of concurrent connections not reduced

Connection state not reset before reuse

Persistent Connection

MySQLClient 1PoolConnection 1

SET @myvar = 1

MySQLClient 2PoolConnection 1

SELECT @myvar

The speaker says...

Persistent connections can be described as a special kind of pooled connections. As the name says, the state of a persistent connection is not reset between use. PHP persistent database connections have often been criticised for persisting the state of a connection... - for their very purpose!

Thus, when persistent connections have been added to the mysqli extension, mysqli actually got pooled connections. By default, the connection state is reset before reuse. Performance fanatics can disable this during compile time.

Speed-up tricks compared

MUXPooled Conn.Pers. Conn

Reduce connection overheadYesYesYes

Reduce # concurrently open connectionsYesNoNo

Connection state shared among clientsYesNoYes
(mysqli: No)

Serialization required, collisions possibleYesNoNo

Every optimization is a trade

You gain something: fewer connections opened

You give something: collision possible

You gain something: lower connection costs

You give something: no isolation of connection state

The speaker says...

Optimizations, such as multiplexing, pooling or persistent connections come at a price. There is no one-fits all trick.

Please, try to understand the properties of each option. Then, decide on a case-by-case basis which technology to use.

Pools are bound to a PHP process

Depending on deployment model,
a PHP process handles one or multiple requests

Remember: scope/life-span

HTTP ServerPHP processPHP processConnection poolConnection poolConn 1Conn 2Conn 3Conn 4

The speaker says...

Operating systems associate file descriptors, including network connections, with processes. At the end of the process, the network connections are closed. Thus, the life-span of every client-side cache/pool of a PHP process is that of the PHP process. No matter whether we are discussing connections cached for multiplexing or persistent connections as found in any of the PHP MySQL APIs (mysql, mysqli, PDO_MySQL).

Depending on the web server deployment model, a PHP process handles one or multiple requests (script runs).

THE END

http://www.slideshare.net/nixnutz/Contact: ulf.wendel@oracle.com, @Ulf_Wendel