Managing Log Files for Distributed Transactions

Updated: April 11, 2008

Applies To: Windows Server 2008

The Microsoft Distributed Transaction Coordinator (MS DTC) uses a log file to monitor and store data for distributed transactions. The log file is a critical part of transaction management because it stores data about unresolved transactions. The DTC uses this data to resolve transactions when a system failure occurs.

To manage system performance, you may have to reset or change the log file size or location. The size of the DTC log file determines the maximum number of concurrent transactions that you can have. For example, on Windows Server 2008, the default log file size is 4 megabytes (MB). After a transaction has committed or aborted, it is deleted from the log file.

When the log file is full, the transaction manager on the local server cannot accept new transactions. The following table describes the double word (DWORD) registry entries that trigger a warning event when the log file is becoming full.

 

Registry value Description

HKEY_LOCAL_MACHINE\Software\Microsoft\DTC\LogWarnEnabled = <enabled>

Set this entry to 1 to enable the warning event.

HKEY_LOCAL_MACHINE\Software\Microsoft\DTC\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.

HKEY_LOCAL_MACHINE\Software\Microsoft\DTC\LogWarnOutLimit = <limit>

Set the entry to the percentage of log usage at which you want to trigger a data event that the log is becoming less full. This entry must be an integer. The default value is 0.

noteNote
You must stop and restart the DTC for these registry settings to take effect.

If the number of current transactions approaches the maximum that you specify, 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.

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 that 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.

This section includes the following tasks for administering the DTC log file:

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