Rollforward Recovery Logging - Fileshare Server

To log updates to one or more files you need to create a database reference file containing the name of the file(s) for which updates are to be logged, and the name of the log file. See the section Database Reference File Maintenance below for details on creating database reference files.

You do not need to include an extension when you specify the log file name as this is generated automatically by the Fileshare Server. If you do specify an extension, the following message is displayed:

FS180-W The log filename specified has an extension. The name of the 
log file has been changed to "filename".

During the logging process the Fileshare Server creates one or more recovery log files. The first recovery log file is called a starter log file, and subsequent log files are called continuation log files. The Fileshare Server creates a continuation log file whenever the current log file is backed up.

The current recovery log file always has an extension beginning with the character "L". A recovery log file that has been backed up has an extension beginning with the character "B". Following either of these letters is a two digit number indicating the recovery log file number, starting at 01. These automatically generated extensions indicate the order in which the log files were written, and hence the order in which they should be applied if a rollforward recovery is performed. For example, suppose you specify a log file called recover. When the Fileshare Server starts up it creates a log file called recover.L01 and logs updates in this file. If the recovery log file is backed up, the Fileshare Server renames the current log file recover.B01 and creates a new one called recover.L02. If the Fileshare Server is shut down, there would be two recovery log files: recover.B01 is called the starter log file and recover.L02 is a continuation log file. There is only ever one starter log file, but there can be any number of continuation log files.

When performing a recovery operation, the Rollforward Recovery Utility processes the starter log file first and then the continuation log files in the order in which they were created.

Updates to data files with entries in the database reference file are logged unless you explicitly turn logging off:

Because of the caching used by some operating systems, not all of the information written to the log file is physically written to disk. The Fileshare Server periodically calls the operating system to force the log file updates to be written. By default, the log file is flushed after every 100 records are written to the log file. You can configure this interval using the /lc (log count) option when you add the log file name to the database reference file. If you specify a log count of zero, the Fileshare Server does not make any calls to the operating system to flush the updates to disk. Instead, the operating system controls the flushing of the log file to disk.

The log file updates are also flushed to disk after every COMMIT operation.

If a transaction was pending at the time of a system failure, the Rollforward Recovery Utility implicitly rolls back the transaction when the files are recovered.

Rollforward recovery logging can severely affect performance. You can use the "/o l" option in the database reference file to switch logging off for those files for which this feature is not essential. Alternatively, you can omit entries for these files from the database reference file altogether.

The recommended method of using recovery logging is:

  1. Each time you want to take a backup of your data files (preferably every day), shut down the Fileshare Server. The Rollforward Recovery Log file(s) contains information about every update made to your database files since the Fileshare Server was started.
  2. Now take a backup of your data files. Once you have backed up your data files, the log file(s) is obsolete (because you only need to log the updates since your last backup) and can be deleted.
  3. Restart the Fileshare Server. It creates a new log file, and any further updates to the files in the database are logged in this new file. In the event of data loss due to a system failure, you can restore your latest database backup and re-apply the updates recorded in the log file(s) using the Rollforward Recovery Utility.

You can have the Fileshare Server automatically perform this sequence of operations for you by specifying a backup directory in the database reference file. See the section Automatic Database Backup and Rollforward Recovery.

If you have a large number of updates being logged, the log file can grow very large. If the disk where the log file resides were to become full, the ability to write records to the log file could be lost. This would result in an incomplete log file forcing the Fileshare Server to close down. A warning is displayed when the amount of free disk space for the log file drops below a certain percentage of the total disk. You can configure this percentage using the /p database reference file option. When you see this warning, close down the Fileshare Server and take a new backup of your data files. This enables you to discard the log file and continue with a new one when the Fileshare Server is restarted.

If you ignore the warning message and the log file continues to grow larger, the Fileshare Server suspends operation when the free disk space available for the log file drops below 200,000 bytes. It displays error message FS030 and waits for the old log file to be backed-up remotely or removed manually before continuing with a new log file.