Explanation of Jet Database for Windows NT 4.0 (165915)

MORE INFORMATION

J<n>.log Files

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.