Tunable Kernel Parameters
NAME [Toc] [Back]
ncsize - number of Directory Name Lookup Cache (DNLC) entries
VALUES [Toc] [Back]
Default [Toc] [Back]
Allowed values [Toc] [Back]
The minimum value allowed is 128. The maximum value allowed is memory
limited. The value is further constrained in that it must be equal to
or greater than eight times the value of the number of locks for the
DNLC (ncsize >= 8 * dnlc_hash_lock).
Specify a positive integer value.
DESCRIPTION [Toc] [Back]
To speed up the search through directories in the kernel, there is a
memory resident cache of directories called the Directory Name Lookup
Cache (DNLC). During a filename lookup in the kernel, any directories
or files encountered are retained in the DNLC for future reference.
The ncsize tunable dictates the number of entries in the DNLC, which
is statically allocated at system boot time. Therefore, the larger
the value of ncsize, the larger the number of directory/file entries
that can be kept cached in memory for filename lookup.
Who Is Expected to Change This Tunable?
HP-UX system administrators.
Restrictions on Changing [Toc] [Back]
This tunable is static. Any changes to the value of this tunable will
require system reboot before taking effect.
When Should the Value of This Tunable Be Raised?
The value may need to be raised to improve filename lookup performance
when running applications which require large numbers of filename
What are the Side Effects of Raising the Value?
More system memory will be consumed for the DNLC.
When Should the Value of This Tunable Be Lowered?
The value can be lowered to limit the number of entries in the DNLC
and reduce memory consumption.
What are the Side Effects of Lowering the Value?
Less system memory will be consumed for the DNLC upon system reboot.
Operations requiring filename lookup (e.g. open(2)) may experience
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: Sep 2004
Tunable Kernel Parameters
What Other Tunable Values Should Be Changed at the Same Time?
The value of ncsize must be equal to or greater than eight times the
value of dnlc_hash_locks (ncsize >= 8 * dnlc_hash_lock).
WARNINGS [Toc] [Back]
All HP-UX kernel tunable parameters are release specific. This
parameter may be removed or have its meaning changed in future
releases of HP-UX.
Installation of optional kernel software, from HP or other vendors,
may cause changes to tunable parameter values. After installation,
some tunable parameters may no longer be at the default or recommended
values. For information about the effects of installation on tunable
values, consult the documentation for the kernel software being
installed. For information about optional kernel software that was
factory installed on your system, see HP-UX Release Notes at
AUTHOR [Toc] [Back]
ncsize was developed by HP.
SEE ALSO [Toc] [Back]
kctune(1M), sam(1M), gettune(2), settune(2), dnlc_hash_locks(5).
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004 [ Back ]