Concurrent Shadow Paging: Snapshots, Read-Only Transactions, and On-The-Fly Multi-Level Incremental Dumping

Shadow paging has a number of desirable properties, of which snapshots are discussed in this paper. It is possible to take a transactionconsistent snapshot of a database in a few microseconds. This can be used to execute arbitrary read-only transactions with full consistency without any locking and only minimal overhead. A related application is dumping the database; it is shown that the page table allows very efficient multi-level incremental dumping of the database without disturbing normal transaction processing. Algorithms are given to solve the associated problems. Modification of snapshots is also discussed; this may turn out to have some interesting applications. 1 Introduction Traditionally, shadow paging has been considered to have poor performance and to be unsuitable for large multi-user systems [3, 7, 11, 12]. However, memory sizes have increased due to technological development, and the entire page table of even a large database can now be kept in main memory. This has re..