Sun Microsystems 820434310 manual LogBufferSize, Tuning DataBufferPoolSize

Tuning HADB

■FreeSize: free size in MB.

■Usage: percent used.

Use the hadbm resourceinfo command to monitor resource usage, for example the following command displays data buffer pool information:

%hadbm resourceinfo --databuf
NodeNo	Avail	Free	Access	Misses	Copy-on-write
0	32	0	205910260	8342738	400330
1	32	0	218908192	8642222	403466

The columns in the output are:

■Avail: Size of buffer, in Mbytes.

■Free: Free size, when the data volume is larger than the buffer. (The entire buffer is used at all times.)

■Access: Number of times blocks that have been accessed in the buffer.

■Misses: Number of block requests that “missed the cache” (user had to wait for a disk read)

■Copy-on-write: Number of times the block has been modified while it is being written to disk.

For a well-tuned system, the number of misses (and hence the number of reads) must be very small compared to the number of writes. The example numbers above show a miss rate of about 4% (200 million access, and 8 million misses). The acceptability of these figures depends on the client application requirements.

Tuning DataBufferPoolSize

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

hadbm set DataBufferPoolSize

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 GlassFish Enterprise Server 2.1 High Availability Administration Guide.

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.

Chapter 6 • Tuning for High-Availability 111