Basic onperf Functions

The onperf utility performs the following basic functions:

• Displays the values of the database server metrics in a tool window
• Saves the database server metric values to a file
• Allows review of the database server metric values from a file

Displaying Metric Values

When onperf starts, it activates the following processes:

• The onperf process. This process controls the display of onperf tools.
• The data-collector process. This process attaches to shared memory and passes performance information to the onperf process for display in an onperf tool.

An onperf tool is a Motif window that an onperf process manages, as Figure 89 shows.

Figure 89. Data Flow from Shared Memory to an onperf Tool Window

Saving Metric Values to a File

The onperf utility allows designated metrics to be continually buffered. The data collector writes these metrics to a circular buffer called the data-collector buffer. When the buffer becomes full, the oldest values are overwritten as the data collector continues to add data. The current contents of the data-collector buffer are saved to a history file, as Figure 90 illustrates.

Figure 90. How onperf Saves Performance Data

The onperf utility uses either a binary format or an ASCII representation for data in the history file. The binary format is host dependent and allows data to be written quickly. The ASCII format is portable across platforms.

You have control over the set of metrics stored in the data-collector buffer and the number of samples. You could buffer all metrics; however, this action might consume more memory than is feasible. A single metric measurement requires 8 bytes of memory. For example, if the sampling frequency is one sample per second, then to buffer 200 metrics for 3,600 samples requires approximately 5.5 megabytes of memory. If this process represents too much memory, you must reduce the depth of the data-collector buffer, the sampling frequency, or the number of buffered metrics.

To configure the buffer depth or the sampling frequency, you can use the Configuration dialog box. For more information on the Configuration dialog box, see the The Graph-Tool Configure Menu and the Configuration Dialog Box.

Reviewing Metric Measurements

You can review the contents of a history file in a tool window. When you request a tool to display a history file, the onperf process starts a playback process that reads the data from disk and sends the data to the tool for display. The playback process is similar to the data-collector process mentioned under Saving Metric Values to a File. However, instead of reading data from shared memory, the playback process reads measurements from a history file. Figure 91 shows the playback process.

Figure 91. Flow of Data from a History File to an onperf Tool Window