ncsize.5 (2010 09)

n
ncsize(5) ncsize(5)
(Tunable Kernel Parameters)
NAME
ncsize - number of Directory Name Lookup Cache (DNLC) entries
VALUES
Failsafe
5596
Default
8976
Allowed values
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
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 dic-
tates 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
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 access.
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 performance degradation.
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
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 parame-
ter 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 http://www.hp.com/go/hpux-core-docs.
AUTHOR
ncsize was developed by HP.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1