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Q165915: Explanation of Jet Database for Windows NT 4.0

Article: Q165915
Product(s): Microsoft Windows NT
Version(s): WinNT:4.0
Operating System(s): 
Keyword(s): kbinfo kbArtTypeINF
Last Modified: 09-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0 
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SUMMARY
=======

Windows Internet Name Service (WINS) produces J<n>.log files in the
%SystemRoot%\System32\Wins folder to increase the speed and efficiency of
storing the WINS data. This article discusses these Jet files and their purpose.

MORE INFORMATION
================

J<n>.log Files
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To increase speed and efficiency of data storage, the Jet database writes current
transactions to log files rather than to the database directly. Therefore, the
most current view of the data will be the database plus any transactions in the
log file(s). These files are also used for recovery if the WINS service is
stopped abruptly or in an unexpected manner. If the service is stopped in an
unexpected manner, the log files will automatically be used to re-create the
correct state of the WINS database.

Log files will always be a certain size; however, they can grow quickly in number
on a very busy WINS Server. It is inevitable that WINS will write more
transactions to a log than the size of the log can accommodate. When a log file
becomes filled, it is renamed to indicate that it is an older log and not in
use. A new transaction log is created with the J<n>.log filename, where
<n> is a decimal number such as J50.log. The naming format of the previous
log file will be JetXXXXX.log, where each X denotes a hexadecimal number from 0
to f. Previous log files are maintained in the same folder as the current log
files.

The log files are processed (all log entries written to the database) and deleted
when a successful backup occurs or when the WINS server is shut down gracefully.
Therefore, if many J<n>.log files have accumulated, frequent backups
should be scheduled to maintain the logs.

After the entries have been processed, it is possible to manually delete the log
files; however, this will prevent a successful recovery of the database if it
should be needed. Because of this, it is important to ensure that the log files
are not manually deleted or removed from the system until a backup has been
performed.

J<n>.chk Files
--------------

Jet maintains a checkpoint file, J<n>.chk, that indicates the location
where the last information was successfully written from the transaction logs to
the database. It is also used for recovery purposes; that is, the checkpoint
file indicates where the recovery or replaying of data should begin. This
checkpoint file is updated every time data is written to the database file
(Wins.mdb).

Res1.log and Res2.log Files
---------------------------

Reserved logs (Res1.log and Res2.log) are kept for emergency purposes. More
specifically, they are used in the event that the server runs out of disk space.
If a server attempts to create another transaction log file and there is
insufficient disk space, the server will flush any outstanding transactions into
these reserved log files. The service will then shut down and log an event to
the Event Viewer.
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Keywords          : kbinfo kbArtTypeINF 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : WinNT:4.0
Issue type        : kbinfo

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