doctrine2/manual/docs/en/improving-performance/bundle-your-class-files.txt

When using Doctrine or any other large OO library or framework the number of files that need to be included on a regular HTTP request rises significantly. 50-100 includes per request are not uncommon. This has a significant performance impact because it results in a lot of disk operations. While this is generally no issue in a dev environment, it's not suited for production. The recommended way to handle this problem is to bundle the most-used classes of your libraries into a single file for production, stripping out any unnecessary whitespaces, linebreaks and comments. This way you get a significant performance improvement even without a bytecode cache (see next section). The best way to create such a bundle is probably as part of an automated build process i.e. with Phing.