Sun Microsystems 820434310 Server User Manual


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Performance
For best performance, all HADB processes (clu_xxx_srv) must t in physical memory. They
should not be paged or swapped. The same applies for shared memory segments in use.
You can congure the size of some of the shared memory segments. If these segments are too
small, performance suers, and user transactions are delayed or even aborted. If the segments
are too large, then the physical memory is wasted.
You can congure the following parameters:
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“DataBuerPoolSize” on page 110
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“LogBuerSize” on page 111
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“InternalLogbuerSize” on page 112
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“NumberOfLocks” on page 113
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“Timeouts” on page 115
DataBuerPoolSize
The HADB stores data on data devices, which are allocated on disks. The data must be in the
main memory before it can be processed. The HADB node allocates a portion of shared
memory for this purpose. If the allocated database buer is small compared to the data being
processed, then disk I/O will waste signicant processing capacity. In a system with
write-intensive operations (for example, frequently updated session states), the database buer
must be big enough that the processing capacity used for disk I/O does not hamper request
processing.
The database buer is similar to a cache in a le system. For good performance, the cache must
be used as much as possible, so there is no need to wait for a disk read operation. The best
performance is when the entire database contents ts in the database buer. However, in most
cases, this is not feasible. Aim to have the “working set” of the client applications in the buer.
Also monitor the disk I/O. If HADB performs many disk read operations, this means that the
database is low on buer space. The database buer is partitioned into blocks of size 16KB, the
same block size used on the disk. HADB schedules multiple blocks for reading and writing in
one I/O operation.
Use the hadbm deviceinfo command to monitor disk use. For example, hadbm deviceinfo
--details will produce output similar to this:
NodeNo TotalSize FreeSize Usage
0 512 504 1%
1 512 504 1%
The columns in the output are:
■
TotalSize: size of device in MB.
TuningHADB
SunGlassFishEnterpriseServer2.1PerformanceTuningGuide • January2009110
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