Managing transaction logging for optimum server availability

This topic describes some considerations and actions that you can use to manage transaction logging to help ensure that the availability of your application servers is optimized.

Why and when to perform this task

The transaction service writes information to the transaction log for every global transaction which 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 application server consists of multiple subdirectories and files held in a single directory. You can change the directory that an application server uses to store the transaction log, as described in Configuring transaction properties for an application server.

When a global transaction is completed, the information in the transaction log is not needed anymore so is marked for deletion. Periodically, this redundant information is garbage collected and the space reused by new transactions. The log files are created of fixed size at server startup, thus no further disk space allocation is required during the lifetime of the server. The default allocation is suitable for around 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 WTRN0083W: 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 Configuring transaction properties for an application server.

Sub-topics
Configuring transaction aspects of servers for optimum availability
Moving a transaction log from one server to another
Restarting a server on a different host