Exchange 2003 Transaction Log File Considerations


Topic Last Modified: 2007-01-08

After Exchange database files are in a Clean Shutdown (Consistent) state, they become independent of the transaction log files for the storage group. To determine the location of the transaction log files for a particular Exchange database, in Exchange System Manager, right-click the desired storage group. In the Properties dialog box, on the General tab, look at the information in the Transaction Log Location and the Log File Prefix fields. For more information about Exchange storage architecture, see Exchange Storage Architecture.

In Exchange terms, they are "detached" from the log files. When you start the database again, it "attaches" them again to a transaction log file. In most cases, it attaches to the same log file that was in use when the database was shut down (although this is not a requirement).

A database can be detached from one series of log files and attached to a different set in a different storage group. If you delete all the log files for a storage group, Exchange will generate a new set of log files, starting with log file 1, and the database attaches to and begins using this new set.

Never delete transaction log files for a storage group unless all databases in the storage group are in a Clean Shutdown state. When a database is in a Dirty Shutdown state, it must have access to the existing log files to be mounted again. If the current log files for a database are destroyed while the database is in Dirty Shutdown state, the only way to restart the database is to use Eseutil /p to perform a repair on it—and even then, repair is not guaranteed.

After a database has detached from its log files and been shut down cleanly, it will never again require the data that already exists in those log files. Everything from the log files has already been written into the database files. However, if you restore a database from backup, you may need the log files again. The older, restored database does not yet have the information from those log files, and you can add that information to the database by "replaying" the logs. The following appendixes explain transaction logging and "no loss" restoration of older databases in greater detail.