Redo Recovery after System Crashes

This paper defines a framework for explaining redo recovery after a system crash. In this framework, an installation graph explains the order in which operations must be installed into the stable database if it is to remain recoverable. This installation graph is a significantly weaker ordering on operations than the conflict graph from concurrency control. We use the installation graph to devise (i) a cache management algorithm for writing data from the volatile cache to the stable database, (ii) the specification of a REDO test used to choose the operations on the log to replay during recovery, and (iii) an idempotent recovery algorithm based on this test; and we prove that these cache management and recovery algorithms are correct. Most pragmatic recovery methods depend on constraining the kinds of operations that can appear in the log, but our framework allows arbitrary logged operations. We use our framework to explain pragmatic methods that constrain the logged operations to reading and writing single pages, and then using this new understanding to relax these constraints. The result is a new class of logged operations having a recovery method with practical advantages over current methods.