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Pro PHP Security: From Application Security Principles to the Implementation of XSS Defenses, Second Edition by Thomas Myer, Michael Southwell, Chris Snyder

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Creating a Versioned Database Filestore

We turn now from versioning for records to versioning for the actual files in which those records are stored.

In the most efficient versioning system, the differences between each successive version are saved along with the latest version. Patching the file with these differences (that is, applying them in reverse) allows any previously saved version of the file to be recovered. We illustrate this concept in Figure 11–1.

As new versions of a file are saved to disk, the version control system saves just the differences between the new version and the previous version. The differences file can be used as a patch, which can be applied to the current version to revert it to the previous one. Because only the ...

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