1. Motivation Isolation-Only Transactions for Mobile Computing

The Unix File System(UFS) has historically offered a shared-memory consistency model. The lack of concurrency control makes this model susceptible to read/write conflicts, i.e., unexpected read/write sharing between two different processes. For example, the update of a header file by one user while another user is performing a long-runningmake can cause inconsistencies in the compilation results. In practice, read/write conflicts are rare for two reasons. First, the window of vulnerability is relatively small because read/write conflicts only occur when the executions of two processes overlap. Second, they are often prevented via explicit user-level coordination. However, the advent of mobile computing makes read/write conflicts a realistic threat to data integrity. Mobile computing is characterized by periods of disconnection and intermittent connectivity[11]. Such communication disturbances greatly widen the window of vulnerability from the life span of a process to the duration of a disconnection. They also significantly reduce the effectiveness of explicit user-level coordination, especially when disconnections are made transparent to users. How can we preserve upward compatibility with the large body of existing Unix software, while offering improved consistency in a mobile computing environment? This position paper puts forth our solution, a new transaction model called isolation only transaction (IOT)