## Technote (FAQ)

## Question

When graphing a large number of data points from my snmpCollect data, the oldest points on the graph are missing. Instead there is a flat line for a ways. How to customize the displayed graph?

## Answer

Much of what is seen on the xnmgraph display can be customized through settings in the "/usr/OV/app-defaults/XNm" file.

" When the maximum number of data points has been exceeded, or when malloc fails and there is no more memory for xnmgraph to store points in, xnmgraph will need to reduce the data. The resource noReducePercent will determine what percent of the data points (from the right side of the graph) will be not reduced. (100-noReducePercent) percent of the data will be reduced each time xnmgraph determines data reduction is required. Increasing noReducePercent will leave more data in a pristine (not reduced) state, at the cost of coarser granularity (less spikes) in older data.

When data is being reduced, it is done at a 2:1 reduction rate. Every two data points are combined into one, preserving the minimum and maximum values, and computing the average. This algorithm will cause each older point's time span to become exponentially larger every time the data is reduced. This keeps the time granularity of newer data fine, while making the time granularity of the oldest data more and more coarse. The larger the noReducePercent is set, the coarser the oldest granularity becomes."

If the old data is to be dropped instead of reduced, use a noReducePercent of 100.

This allows control of how xnmgraph reacts to large amounts of data or to memory ceilings. The the number of data points can be managed by using larger data sampling intervals. But there is little control over how much memory is available to satisfy xnmgrap's malloc requests or when the memory is needed.