AIX Version 4.3 Differences Guide

specified socket. The system call dynamically caches the data in the NBC, thus
improving performance for files that are sent frequently across the network, and
which do not change often. This feature can be disabled on a file by file basis.
The application sending the data will need to be altered to use the send_file call.
The greatest improvement in performance can be gained by using direct I/O to
read the file that is to be transmitted. This can be achieved simply by opening the
file using the O_DIRECT flag. This flag enables send_file to bypass the JFS
cache when reading the file, thus further reducing the number of data transfers
required.
The size of the NBC, and various cache tuning parameters can be altered using
the no command. The options that can be changed are:
nbc_limit
nbc_max_cache
Maximum size of the NBC. Specifies in KB the maximum
amount of memory that can be used for the NBC. The
default value is derived from the size of the mbuf pool
(thewall), which in turn, is determined from the amount of
physical memory. If a system has less than 512 MB of
memory, the default value of nbc_limit is 0.
Maximum size of a cache object in the NBC. Specified in
bytes, default value is 131072 (128 KB) bytes.
nbc_min_cache Minimum size of a cache object in the NBC. Specified in
bytes, default value is 1.
send_file_duration Specifies the cache validation duration for all the file objects
that system call send_file accessed in the Network Buffer
Cache. This attribute is in number of seconds, the default is
300 for 5 minutes. 0 means that the cache will be validated
for every access.
Cache statistics can be viewed using the command netstat -c. Sample output is
shown in Figure 9.
Figure 9. Sample Output from netstat -c Command
Application Development and Pthreads 81