Index

Configuring general properties of the viewer

There are a couple of properties that globally effect the viewer. These are the sub-sampling interval to use when reading data, and the size of the plot buffer.

Sub-sampling the incoming data

Sub-sampling of the data can be used to speed up reading from the archive. To disable sub-sampling, specify this as 1. A sub-sampling interval of n means that every n'th sample is read.

Setting the size of the plot buffer

The viewer contains a circular buffer which maintains plotted data in memory. Its size is specified as the number of register values that can be stored in the buffer. By default this is 500000. These 500000 elements are then divided up between all of the registers that are being plotted. For example, if one were to have 4 graphs, each one displaying a single register, then these 4 registers plus the x-axis register constitute 5 registers to be stored, per snapshot received from the control program. Thus one could display 100000 points per graph. Beyond this point, the oldest data is deleted to make way for new data as it arrives. Clearly the larger you make this buffer, the more data you will be able to display. Unfortunately enlarging the buffer doesn't come without consequences. Excessive memory usage can make the computer thrash when you replot a graph, and replotting or zooming a graph with a lot of points can be painfully slow.

Martin Shepherd (6-Nov-1999)