User-level operating system transactions

User-level operating system transactions allow system administrators and ordinary users to perform a sequence of file operations and then commit them as a group, or abort them without leaving any trace behind. Such a facility can aid many system administration and software development tasks. The snapshot isolation concurrency control mechanism allows transactions to be implemented without locking individual system calls; conflicts are detected when the transaction is ready to commit. Along these lines we have implemented a user-space transaction monitor that is based on ZFS snapshots and a file system event monitor. Transactions are committed through a robust and efficient algorithm that merges the operations performed on a file system’s clone back to its parent. Both the performance impact and the implementation cost of the transaction monitor we describe are fairly small.