InternalLogbufferSize

The node internal log (nilog) contains information about physical (as opposed to logical, row level) operations at the local node. For example, it provides information on whether there are disk block allocations and deallocations, and B-tree block splits. This buffer is maintained in shared memory, and is also checked to disk (a separate log device) at regular intervals. The page size of this buffer, and the associated data device is 4096 bytes.

Large BLOBs necessarily allocate many disk blocks, and thus create a high load on the node internal log. This is normally not a problem, since each entry in the nilog is small.

Tuning InternalLogbufferSize

Begin with the default value. Look out for HIGH LOAD informational messages in the history files. The relevant messages contain nilog, and a description of the internal resource contention that occurred.

Use the following command to display node internal log buffer information:

hadbm resourceinfo --nilogbuf

For example, the output might look something like this:

Node No.     Avail         Free Size
0            11            11
1            11            11

To change the size of the nilog buffer, use the following command:

hadbm set InternalLogbufferSize

The hadbm 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 8.2 High Availability Administration Guide.

If the size of the nilog buffer is changed, the associated log device (located in the same directory as the data devices) also changes. The size of the internal log buffer must be equal to the size of the internal log device. The command hadbm set InternalLogBufferSize ensures this requirement. It stops a node, increases the InternalLogBufferSize, re initializes the internal log device, and brings up the node. This sequence is performed on all nodes.