Tuning HP Tru64 UNIX V5.1A and V5.1B for Oracle

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The recommended value for ubc_maxpercent should be at least 70%, but less than 100%, and
should not be set to a value smaller than 35%.
ubc_minpercent
The value for this parameter represents the minimum amount of memory available for the UBC. When
this parameter is set to a very low value, it may cause severe performance problems on buffered file
system operations such as file copies. This is especially true on NUMA systems where the UBC is
distributed over the Resource Affinity Domains (RAD)s.
The recommended value for ubc_minpercent is to leave it at its default value of 10%.
ubc_borrowpercent
The value for this parameter represents a percentage of memory above which the UBC is only
borrowing memory from the virtual memory subsystem. Paging does not occur until the UBC has
returned all its borrowed pages. The default value of 20% is usually a good fit for most systems.
vm_ubcseqpercent
This parameter controls the maximum percentage of UBC memory that can be used to cache a single
file.
The default value of 10% is usually a good fit for most systems.
vm_ubcseqstartpercent
This parameter is a percentage of the UBC in terms of its current size that determines the threshold at
which the UBC starts to check whether the percentage of UBC pages cached for each file object has
been exceeded (as specified by vm_ubcseqpercent). If the cached page percentage for any file
exceeds the value of vm_ubcseqpercent, the UBC returns that file's UBC Least Recently Used (LRU)
pages to virtual memory.
Prior to HP Tru64 UNIX V5.x, the vm_ubcseqpercent and vm_ubcseqstartpercent
parameters were a percentage of total memory.
The recommended value is to keep vm_ubcseqstartpercent at the default of 50%.
vm_ubcdirtypercent
This parameter specifies the percentage of pages that can be dirty (modified) before the UBC must
flush them to disk. The default value of 10% usually works very well for most systems. However, on
systems with lots of file system/UBC activity, increasing the value for this parameter may increase the
ability to re-read from the file system cache.
The recommended value for vm_ubcdirtypercent is to keep the default value of 10%, but on
systems that could benefit from keeping file system pages in the UBC you could increase it to 90%.
vm_swap_eager
This parameter controls how the system will use the available swap space. For a database server
environment the swap allocation mode could be changed from eager (the default) to deferred (lazy)
swap mode.
The minimal size of swap space that should be allocated is equal to the size of physical memory plus
10%.
Setting vm_swap_eager = 1 (the default) indicates that the system is in `eager swap' allocation
mode. On systems with an undetermined workload, you may want to allocate a swap space with a
size between two and three times the size of physical memory. Use eager swap allocation mode for
highly reliable systems that overcommit memory resources.