15.1 Limit Enabled Probes

Dynamic instrumentation techniques enable DTrace to provide unparalleled tracing coverage of the kernel and arbitrary user processes. While this coverage provides revolutionary new insight into system behavior, it also can cause enormous probe effect. If tens of thousands or hundreds of thousands of probes are enabled, the effect on the system can easily be substantial. Therefore, you should only enable as many probes as you need to solve a problem. For example, you should not enable all syscall probes if a more concise enabling can answer your question. Your question might require that you concentrate on a specific module of interest or a specific function.

Caution

When using the pid provider, be especially careful. Because the pid provider can instrument every instruction, you could enable millions of probes in an application and therefore slow the target process to a crawl.

You can also use DTrace in situations where large numbers of probes must be enabled to answer a question. Enabling a large number of probes might slow down the system significantly, but it never induces fatal failure on the system. You should therefore not hesitate to enable many probes, if so required.