Data recovery for web applications

Web-based applications store their data at the server side. This design has several benefits, but it can also cause a serious problem because a misconfiguration, bug or vulnerability leading to data loss or corruption can affect many users. While data backup solutions can help resolve some of these issues, they do not help diagnose the events that led to the corruption or the precise set of changes caused by these events. In this paper, we describe the design of a recovery system that helps administrators recover from data corruption caused by bugs in web applications. Our system tracks application requests, helping identify requests that cause data corruption, and reuses undo logs already kept by databases to selectively recover from the effects of these requests. The main challenge is to correlate requests across the multiple tiers of the application to determine the correct recovery actions. We explore using dependencies both within and across requests at three layers (database, application, and client) to help identify data corruption accurately. We evaluate our system using known bugs in popular web applications, including Wordpress, Drupal and Gallery2. Our results show that our system enables recovery from data corruption without loss of critical data and incurs small runtime overhead.