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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 .
Log shipping is the process of automating the backup of transaction log files on a primary (production) database server, and then restoring them onto a standby server. This technique is supported by Microsoft SQL Server , [ 1 ] 4D Server , [ 2 ] MySQL , [ 3 ] and PostgreSQL .
A write ahead log is an append-only auxiliary disk-resident structure used for crash and transaction recovery. The changes are first recorded in the log, which must be written to stable storage, before the changes are written to the database. [2] The main functionality of a write-ahead log can be summarized as: [3]
A server log is a log file (or several files) automatically created and maintained by a server consisting of a list of activities it performed. A typical example is a web server log which maintains a history of page requests. The W3C maintains a standard format (the Common Log Format) for web server log files, but other proprietary formats ...
Microsoft SQL Server (Structured Query Language) is a proprietary relational database management system developed by Microsoft.As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which may run either on the same computer or on another computer across a network (including the Internet).
For example, MySQL began supporting transactions from early version 3.23, but the InnoDB storage engine was not default before version 5.5. The earlier available storage engine, MyISAM does not support transactions. A transaction is typically started using the command BEGIN (although the SQL standard specifies START TRANSACTION).
For example, a transfer of funds from one bank account to another, even involving multiple changes such as debiting one account and crediting another, is a single transaction. In 1983, [ 1 ] Andreas Reuter and Theo Härder coined the acronym ACID , building on earlier work by Jim Gray [ 2 ] who named atomicity, consistency, and durability, but ...
Transaction-processing systems ensure database integrity by recording intermediate states of the database as it is modified, then using these records to restore the database to a known state if a transaction cannot be committed. For example, copies of information on the database prior to its modification by a transaction are set aside by the ...