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Manage transaction logging for optimum server availability

 

This topic describes how to manage transaction logging to optimize the availability of your appservers.

 

Overview

The transaction service writes information to the transaction log for every global transaction that involves two or more resources, or is distributed across multiple servers. The transaction log is stored on disk and is used by the transaction service for recovery after a system or server crash. The transaction log for each appserver consists of multiple subdirectories and files held in a single directory. You can change the directory that an appserver uses to store the transaction log, as described in Configuring transaction properties for an appserver.

When a global transaction is completed, the information in the transaction log is no longer required, and the information is marked for deletion. The redundant information is garbage collected and intervals, and the space is reused by new transactions. The log files are created with a fixed size at server startup, so no further disk space allocation is required during the lifetime of the server. The default disk space allocation provides for approximately 4000 concurrent transactions.

If all the log space is in use when a transaction needs to save information, the transaction is rolled back and the message CWWTR0083W: The transaction log is full. Transaction rolled back. is reported to the system error log. No more transactions can commit until more log space is made available when existing active transactions complete.

You can monitor the number of concurrent global transactions by using the performance monitoring counters for transactions. The "Global transaction commit time" counter is a measure of how long a transaction takes to complete and, therefore, how long the log is in use by a transaction. If this value is high, then transactions are taking a long time to complete, which can be due to resource manager or network failures. If you ensure that this value is low, the log is more efficiently used and unlikely to become full.

You can change the default size of log files by updating the transaction log settings as described in Configure transaction properties for an appserver.

Use the following tasks to manage transaction logging to optimize the availability of your appservers:

 

Procedure



Configure transaction aspects of servers for optimum availability

Moving a transaction log from one server to another

Restarting a server on a different host

 

Related tasks


Configure transaction properties for an appserver
Using transactions with WebSphere applications