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System Management Release Notes
4.6 Performance Enhancements
WBM_MSG_LOWER is the threshold used to determine if a switch should occur
to single message mode, when operating in buffered message mode. If WBM_
MSG_LOWER or fewer SetBit operations are done in a 100 millisecond window,
the messaging mode will be switched to single mode. The default value is 20.
4.6.1.3 Asynchronous SetBit Messages
V8.4
There can be multiple master bitmap nodes for a shadow set. Currently, SetBit
messages are sent to the multiple master bitmap nodes synchronously. Only
when the response for the SetBit message is received from the first remote
master bitmap node, is the message sent to the next master bitmap node. When
done with all of the remote master bitmap nodes, the I/O is resumed.
SetBit messages are now sent to all multiple master bitmap nodes
asynchronously. I/O operation is resumed when the responses from all the master
bitmap nodes are received. This reduces the stall time of the I/O operation by the
write bitmap code.
4.6.1.4 Reduced SetBit Messages for Sequential I/O
V8.4
If sequential writes occur to a disk, it results in sending Setbit messages that set
sequential bits in the remote bitmap. The WBM code will now recognize where
a number of prior bits in the bitmap have already been set. In this scenario, the
WBM code will set additional bits so that if sequential writes should continue,
fewer Setbit messages are required. Assuming the sequential I/O continues,
the number of Setbit messages will be reduced by about a factor of 10 and thus
improve the I/O rate for sequential writes.
4.6.2 Exception Handling Performance Improvements (Integrity servers Only)
V8.4
The OpenVMS Version 8.4 caches the decoded unwind data. The cache is used
in the user-callable calling standard routines, during the exception handling.
These calling standard routines are also used in the RTLs, to implement
programming language constructs like the try/throw/catch constructs in C++ and
the setjmp/longjmp constructs in C programming language.
In case of unexpected errors, the cache can be disabled temporarily using the
VMS system parameter, KTK_D3. Its default value of zero enables the cache. A
value of one disables the cache. The special parameter, KTK_D3 may have been
used by HP supplied debug/test images. If you had such test images on your
system, make sure that it is reset to its default value zero. The ability to disable
the cache will be removed in the OpenVMS Version 8.4 main release.
4.6.3 Exception Handling (Integrity servers Only)
Some performance improvements have been made to exception handling for
OpenVMS Integrity server systems. The change will reduce the overhead of
exception handling in some, but not all cases of exception handling.
System Management Release Notes 4–9