Tuning HADB
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 GlassFish Enterprise Server 2.1 High Availability Administration Guide.
Note – 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.
NumberOfLocks
Each row level operation requires a lock in the database. Locks are held until a transaction commits or rolls back. Locks are set at the row (BLOB chunk) level, which means that a large session state requires many locks. Locks are needed for both primary, and mirror node operations. Hence, a BLOB operation allocates the same number of locks on two HADB nodes.
When a table refragmentation is performed, HADB needs extra lock resources. Thus, ordinary user transactions can only acquire half of the locks allocated.
If the HADB node has no lock objects available, errors are written to the log file. .
Chapter 6 • Tuning for | 113 |
