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A database transaction symbolizes a unit of work, performed within a database management system (or similar system) against a database, that is treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main purposes:
Physically, a log is a file listing changes to the database, stored in a stable storage format. If, after a start, the database is found in an inconsistent state or not been shut down properly, the database management system reviews the database logs for uncommitted transactions and rolls back the changes made by these transactions ...
Alternatively, the messages may be written to a dedicated logging system or to a log management software, where it is stored in a database or on a different computer system. Specifically, a transaction log is a log of the communications between a system and the users of that system, [2] or a data collection method that automatically captures ...
Transaction processing is designed to maintain a system's Integrity (typically a database or some modern filesystems) in a known, consistent state, by ensuring that interdependent operations on the system are either all completed successfully or all canceled successfully.
If a crash happens during that later write operation, previously stored log data may be lost. The ping-pong scheme described in Transaction Processing [1] eliminates this problem by alternately writing the contents of said (logical) last page to two different physical pages inside the log file (the actual last page i and its empty successor i+1).
Temporal database; Thomas write rule; Three-phase commit protocol; Timestamp-based concurrency control; Timestamping (computing) Transaction data; Transaction log; Transaction Processing Facility; Transaction processing system; Transaction time; Transaction Workflow Innovation Standards Team; Transactional memory; Transactional NTFS
The log file structure is very robust against system crashes. Recovery is the process of using this log to restore databases to a consistent state after a system crash. Transaction operations are logged and the log is flushed to disk during each commit to transaction level 0.
The following features are desirable in a database system used in transaction processing systems: Good data placement: The database should be designed to access patterns of data from many simultaneous users. Short transactions: Short transactions enables quick processing. This avoids concurrency and paces the systems.