Sampling Preferences

The Sampling tab, illustrated in Figure 2-1, allows you to modify the default sampling interval and sampling buffer sizes for the graphs in new System Windows by specifying new values for these two numbers in the supplied text boxes. As indicated, all values are in seconds.

Chart Preferences

The Chart tab, illustrated in Figure 2-2, provides controls to change the appearance of the charts displayed in each System Window. The options are divided into four groups, which are discussed in turn below.

1. Axis Appearance— This group of controls sets the appearance of the two axes in each chart. Separate but identical sets of controls are supplied for each axis. All options are simple on-off flags, chosen with checkboxes:

   • Major Lines— If checked, puts lines on the major divisions of the chart’s axis.

   • Minor Lines— If checked, puts lines on the minor divisions of the chart’s axis.

   • Major Ticks— If checked, puts small lines on the axis line to show where the major divisions are.

   • Minor Ticks— If checked, puts small lines on the axis line to show where the minor divisions are.

   • Labels— If checked, puts displays text on the axis next to each major division that describes the division. In general, you will almost always want this for the Y-axis, but it is usually less useful for the X-axis.

2. X Axis Time Display— This is just a single set of radio buttons that controls how time is displayed on the X axis:

   • Relative Time— If selected (the default), BigTop displays time relative to the point in time that statistics collection was initiated. You will see the time start at 0 in each new window and progress upwards. This mode is useful when you start BigTop and your workload off simultaneously.

   • Absolute Time— If selected, BigTop will print the 24-hour wall-clock time along the X axis, allowing you to see the actual time-of-day when the statistics were taken. This mode is better for monitoring a system continually over extended periods of time.

3. Y Axis Numerical Display— These controls vary how numbers are presented on the Y axis. The controls consist of a mixture of a checkbox and a set of radio buttons:

   • Log— Normally BigTop uses a linear graph scale on the Y-axis. If checked, changes the vertical axis to be logarithmic. This may be useful in some cases where you are tracking two different trends that are orders of magnitude apart in value.

   • Independent— If selected (the default), each data line is plotted independently as a distance from the 0 point on the y-axis.

   • Stacked value— If selected, BigTop plots the lines more like a stacked-bar or area plot. The first data line is plotted as the distance from the 0 point on the y-axis. The second data line is plotted as a distance from the first data line on the y-axis. This continues for each subsequent data line. This mode is more useful when you are interested in the sum of the parts instead of each individual part

4. Drawing Controls— These modulate options relating to how Bigtop draws its chart:

   • Legend— When checked, BigTop displays a box containing a description of what each data line represents. Using the pop-up menu to the right, you can choose the position for this legend: to the top, bottom (the default), left, or right of the chart itself.

   • Canvas— When checked, BigTop fills the background of the chart with a color or gradient, using the colors supplied in the color wells just below. The plain “start” or “end” colors may be selected, or you can choose gradients between “start” and “end” running in several directions: vertical (bottom-to-top), horizontal (left-to-right), diagonal-right (lower left to upper right), or diagonal-left (upper right to lower left).

   • Start Color— When using a gradient background, this well sets the “start” color. Clicking it brings up the standard Mac OS X color picker.

   • End Color— This is the “end” color for any background gradients.