DTC Log File Management
The DTC uses a log file to monitor and store statistics for distributed transactions. The log file is a critical part of transaction management because it stores information about unresolved transactions—information that the DTC uses to resolve transactions in the event of system failures.
To manage system performance, you may need to reset or change the log file size or location. The size of the DTC log file determines the maximum allowable number of concurrent transactions. (For example, on Microsoft Windows 2000 Server, the default log file size is 4 MB.) After a transaction has committed or aborted, it is deleted from the log file.
If the log file becomes full, the transaction manager on the local server cannot accept any new transactions. You can trigger a warning event when the log file is becoming full by creating the following three DWORD registry entries:
LogWarnEnabled = <enabled>
Set this entry to 1 to enable the warning event.
LogWarnInLimit = <limit>
Set this entry to the percentage of log usage at which you want to trigger the warning event that the log is becoming full. This entry must be an integer. The default value is 100.
LogWarnOutLimit = <limit>
Set the entry to the percentage of log usage at which you want to trigger an information event that the log is becoming less full. This entry must be an integer. The default value is 0.
The DTC must be stopped and restarted for these registry settings to take effect.
If the number of current transactions approaches the specified maximum, you can increase the size of the log file to allow for more transactions. Conversely, if the number of current transactions is well below the maximum, you can decrease the size of the log file to conserve disk space. You might also be able to improve performance by moving the log file to a location where disk space is high or processing demands are low.
On Windows 2000 Server, Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008, Windows°7, Windows Server 7, Windows Next, and Windows Next Server, the default DTC log file size is 4 MB. For most systems, the default DTC log file sizes are adequate. However, if you want to change the log file size, you can use the following guidelines to determine the size of your DTC log file:
Allocate 1 MB of log space for every 1,000 transactions that are active concurrently.
Allocate 1 MB of log space for every 500 Oracle, IBM DB2, Informix, Sybase, or CA Ingres database connections your applications open concurrently.
These guidelines are conservative. The actual amount of disk space that each DTC log file record requires depends on how many resource managers and subordinate transaction managers are enlisted in the transaction. In addition, the DTC maintains large reserves of available space in the DTC log file to ensure that it always has adequate log space to commit or abort any transaction that it has previously initiated.
The following topics in this section provided detailed information about administering the DTC log file: