The DNLC Hit Ratio

A commonly overlooked resource is the directory name lookup cache. If the cache hit ratio is too low, an increase in the size of the cache can improve performance. On older operating systems, SarCheck will report the percent of directory names that were too long to be cached.

The DNLC hit ratio, as calculated from the sar -a statistics, was 97.95 percent. Due to the presence of low numbers in the iget/s or namei/s fields of the sar -a report, this hit ratio is likely to be inaccurate. As a result, the current DNLC hit ratio has been calculated using real time kernel statistics, and the current hit ratio is 88.48 percent. As a rule, if the DNLC ratio is much less than 90 percent, an increase in the value of ncsize will be recommended. The disadvantage of using kernel statistics is that they represent real time data, not data collected at the same time as the sar and ps statistics.