An intent log is a mechanism used to make
computer operations more resilient in the event of failures. They are used in
database software
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spa ...
, transaction managers, and
some file systems. In database area,
transaction log
In the field of databases in computer science, a transaction log (also transaction journal, database log, binary log or audit trail) is a history of actions executed by a database management system used to guarantee ACID properties over crashes ...
is widely used. In file system area, intent log is used more often.
Before performing an operation, a record of the intent to perform it is written, usually to some relatively permanent medium such as a
hard disk drive
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
. After the operation is performed, another record is written. Usually, an operation will change some data in a system. In some cases, the intent record will contain a copy of the data before and after the operation.
This adds overhead, sometimes a significant amount. Enough data is written to the log to either redo or to undo the operation later.
If a failure occurs, then when the system is recovering, it can use the intent log to detect what operations were still in process during the failure, and use the intent log to help recover from the failure, usually by either undoing a partially completed operation, or by redoing one that might need to be completed.
See also
*
Journaling file system
A journaling file system is a file system that keeps track of changes not yet committed to the file system's main part by recording the goal of such changes in a data structure known as a " journal", which is usually a circular log. In the even ...
*
Write-ahead logging
In computer science, write-ahead logging (WAL) is a family of techniques for providing atomicity and durability (two of the ACID properties) in database systems. A write ahead log is an append-only auxiliary disk-resident structure used for crash ...
References
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Transaction processing