Database Systems: The Intelligent Store: A Content-Addressable Page Manager

1.1 Overview The Intelligent Store (is) is a page manager for an experimental 2567 local computer network.1 Typical clients of the is are a database manager or a file manager. The is provides concurrent, transactionoriented, read-write-search access to a large database of pages. If a hardware or software crash occurs, the is restores the database to its most recent consistent state. Note that the is is a low-level component of a Database Management System (DBMS). Normally there will be several additional layers of DBMS software between the is and end users or application programs. The is is transaction-oriented. Clients can start transactions, read or write pages for transactions, or commit or abort transactions. Many transactions can be active simultaneously, and each transaction can read and write an arbitrary number of pages. Writes for a transaction are not effective until (and unless) the transaction commits. The is ensures that commit is atomic and permanent, in spite of crashes. "Atomic" means that either all writes become effective, or else none do. "Permanent" means that once the is says that a transaction has been committed, its writes will not be lost, even if the is crashes immediately. Aborting a transaction undoes all its effects. If a client crashes, the is automatically aborts all of that client's uncommitted transactions. If the is crashes, the is will (eventually) abort all uncommitted transactions. Furthermore, the is reserves the right to abort any uncommitted transaction at any time (for cause, of course, but the client has no appeal).