Removed Extensions
New Global Constants
Migrating from PHP 5.3.x to PHP 5.4.x
PHP Manual

## Other changes to extensions

Changes in extension behavior, and new features:

- mysqli - mysqli_result now implements Traversable

- pdo_mysql - Removed support for linking with MySQL client libraries older than 4.1

- The MySQL extensions mysql, mysqli and PDO_mysql use mysqlnd as the default library now. It is still possible to use libmysqlclient by specifying a path to the configure options.

- mysqlnd - Added named pipes support

Removed Extensions
New Global Constants
Migrating from PHP 5.3.x to PHP 5.4.x
PHP Manual