Operating Systems: Concurrent and Distributed Software Design

15.8. A single operation on persistent data

For most of Part II we have considered the case where the data structures accessed by concurrent processes reside in main memory. In order to consider the effects of crashes we have started to look at the externally visible effects of operations. We have therefore begun to focus on persistent store. Figure 15.5 shows an operation (specified as part of a module's interface) operating on persistent data. An example is an implementation of an airline booking system, as used in Section 9.7.1, where we focused on the value in main memory of the variable unbooked-seats. In fact, the information on a particular flight would be retrieved from persistent memory before being tested and updated in main memory: ...