Server User Manual

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FreeSize: free size in MB.
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Usage: percent used.
Use the hadbm resourceinfo command to monitor resource usage, for example the
following command displays data buer 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:
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Avail: Size of buer, in Mbytes.
■
Free: Free size, when the data volume is larger than the buer. (The entire buer is used at all
times.)
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Access: Number of times blocks that have been accessed in the buer.
■
Misses: Number of block requests that “missed the cache” (user had to wait for a disk read)
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Copy-on-write: Number of times the block has been modied 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 gures
depends on the client application requirements.
Tuning DataBuerPoolSize
To change the size of the database buer, use the following command:
hadbm set DataBufferPoolSize
This command restarts all the nodes, one by one, for the change to take eect. For more
information on using this command, see “Conguring HADB” in Sun GlassFish Enterprise
Server 2.1 High Availability Administration Guide.
LogBuerSize
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 buer. 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.
Tuning HADB
Chapter 6 • Tuning for High-Availability 111