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Encyclopedia > Common Log File System

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 OSs. CLFS can be used for both data logging as well as for event logging. CLFS is used by TxF and TxR to store transactional state changes before they commit a transaction. In processors with memory protection, kernel mode (as opposed to user mode) is the mode in which the operating system kernel runs. ... User mode refers to two similar concepts in computer architecture. ... A database transaction is a unit of interaction with a database management system or similar system that is treated in a coherent and reliable way independent of other transactions. ... Windows Server 2003 is a server operating system produced by Microsoft. ... “Windows” redirects here. ... This article or section does not cite any references or sources. ... Microsofts latest Windows operating system, Windows Vista, includes a number of new I/O technologies and enhancements that are intended to shorten the time taken to boot the system, improve the responsiveness of the system, and improve the reliability of data storage. ...


The job of CLFS, like any other transactional logging system, is to record a series of steps required for some action so that they can be either played back accurately in the future to commit the transaction to secondary storage or undone if required. CLFS first marshals logs records to in-memory buffers and then writes them to log-files on secondary storage (stable media in CLFS terminology) for permanent persistence. When the data will be flushed to stable media is controlled by built-in policies, but a CLFS client application can override that and force a flush. CLFS allows for customizable log formats, expansion and truncation of logs according to defined policies, as well as simultaneous use by multiple client applications. CLFS is able to store log files anywhere on the file system.[1] See serial publication for the term in publishing In computer science, serialization means to force one-at-a-time access for the purposes of concurrency control, or to encode a data structure as a sequence of bytes. ... In computer storage, secondary storage, or external memory, is computer memory that is not directly accessible to the central processing unit of a computer, requiring the use of computers input/output channels. ...

CLFS defines a device driver interface (DDI), via which physical storage system specific drivers plug in to the CLFS API. The CLFS driver implements the ARIES recovery algorithm; other algorithms can be supported by using custom drivers.[1] Windows XP loading drivers during a Safe Mode bootup A device driver, or software driver is a computer program allowing higher-level computer programs to interact with a computer hardware device. ... An interface is a specification that exists between software components that specifies a selected means of interaction, by means of properties of other software modules, which abstract and encapsulate their data. ... In computer science, Algorithms for Recovery and Isolation Exploiting Semantics, or ARIES is a recovery algorithm designed to work with a no-force, steal database approach. ...

CLFS supports both dedicated logs, as well as multiplexed logs. A dedicated log contains a single stream of log records whereas multiplexed log contain multiple streams, each stream for a different application. Even though a multiplexed log has multiple streams, logs are flushed to the streams sequentially, in a single batch. CLFS can allocate space for a set of log records ahead-of-time (before the logs are actually generated) to make sure the operation does not fail due to lack of storage space.[1]

A log record in a CLFS stream is first placed to Log I/O Block in a buffer in system memory. Periodically blocks are flushed to stable storage devices. On the storage device, a log contains a set of Containers, which are allocated contiguously, each containing multiple Log I/O Blocks. New log records are appended to the present set. Each record is identified by a Log Sequence Number (LSN), an increasing 32-bit sequence number. The LSN and other metadata are stored in the record header. The LSN encodes the identifier of the container, the offset to the record and the identifier of the record - these information is used to access the log record subsequently. However, the container identifiers are logical identifiers, they must be mapped to physical containers. The mapping is done by CLFS itself.[2]


  1. ^ a b c Introduction to the Common Log File System. MSDN. Retrieved on 2007-10-26.
  2. ^ CLFS Stable Storage. MSDN. Retrieved on 2007-10-26.

The Microsoft Developer Network (MSDN) is an information service from Microsoft for software developers. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 299th day of the year (300th in leap years) in the Gregorian calendar. ... The Microsoft Developer Network (MSDN) is an information service from Microsoft for software developers. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 299th day of the year (300th in leap years) in the Gregorian calendar. ...

External links

  • Common Log File System
  • Fast and Flexible Logging with Vista's Common Log File System



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