The Zend Optimizer+ opcode caching and optimization is now available for open source use under the PHP License. Until now, you could only use it as closed source as part of Zend Server.
Zend Optimizer+ improves the speed of PHP execution through opcode caching. It improves server performance by storing compiled PHP bytecode in shared memory, so when used a second time the code doesn’t have to be read from the disk or compiled.
Recently, Zend CTO Zeev Suraski put forward a proposal on the PHP wiki for integrating the Zend Optimizer+ component into the Open Source PHP distribution.
His RFC (request for comments) says that Optimizer+ offers a consistently better performance than its main rival, APC, with improvements of between 5 and 20 per cent in terms of requests per second. The RFC also says that Optimizer+ is typically fully compatible with PHP releases even before they come out because of the work Zend does on PHP.
“While this advantage was rarely realized because of the closed-source nature of the component, once open-source, both Zend and the community will help ensure that it’s always fully compatible with every element of the PHP language, avoiding any lags.”
APC, the Alternative PHP Cache, has also been put forward to be included as a native part of PHP 6.0. APC has the advantages of having a data caching API, and of reclaiming memory associated with scripts that are no longer in use.