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Common Log File System (CLFS) is a general-purpose logging subsystem that is accessible to both kernel-mode as well as user-mode applications for building high-performance transaction logs. It was introduced with Windows Server 2003 R2 and included in later Windows operating systems.
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]
Both the database and log files are check summed to ensure that no data corruptions exist within the data set during the backup process. Streaming backups may also be incremental backups. Incremental backups are ones in which only the log files are copied and which can be restored along with a previous full backup to bring all databases to a ...
Re-doing a transaction in this context simply means applying the information in the redo log files to the database; the system does not re-run the transaction itself.) The system thus re-creates committed transactions by applying the “after image” records in the redo log files to the database, and undoes incomplete transactions by using the ...
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This makes it possible to do a clean backup of the checkpoint state while transactions proceed on the commit state. A transaction log file records all transactions since the last checkpoint. Transaction log files may be preserved and archived for an indefinite time, providing a full, recoverable history of the database.