Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Performance Tuning Guide

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### LogBufferSize

Before it executes them, HADB logs all operations that modify the database, such as inserting, deleting, updating, or reading data. It places log records describing the operations in a portion of shared memory referred to as the (tuple) log buffer. HADB uses these log records for undoing operations when transactions are aborted, for recovery in case of node crash, and for replication between mirror nodes.

The log records remain in the buffer until they are processed locally and shipped to the mirror node. The log records are kept until the outcome (commit or abort) of the transaction is certain. If the HADB node runs low on tuple log, the user transactions are delayed, and possibly timed out.

#### Tuning LogBufferSize

Begin with the default value. Look for `HIGH LOAD` informational messages in the history files. All the relevant messages will contain `tuple log` or simply `log`, and a description of the internal resource contention that occurred.

Under normal operation the log is reported as 70 to 80% full. This is because space reclamation is said to be “lazy.” HADB requires as much data in the log as possible, to recover from a possible node crash.

Use the following command to display information on log buffer size and use:

    hadbm resourceinfo --logbuf

For example, output might look like this:

    Node No.     Avail         Free Size
    0            44            42
    1            44            42

The columns in the output are:

- Node No.:The node number.

- Avail: Size of buffer, in megabytes.

- Free Size: Free size, in MB, when the data volume is larger than the buffer. The entire buffer is used at all times.

  Change the size of the log buffer with the following command:

      hadbm set LogbufferSize

  This command restarts all the nodes, one by one, for the change to take effect. For more information on using this command, see Configuring HADB in Sun Java System Application Server Enterprise Edition 8.1 2005Q2 High Availability Administration Guide.

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