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Solaris Dynamic Tracing Guide
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Document Information


1.  Introduction

2.  Types, Operators, and Expressions

3.  Variables

4.  D Program Structure

5.  Pointers and Arrays

6.  Strings

7.  Structs and Unions

8.  Type and Constant Definitions

9.  Aggregations

Aggregating Functions


Printing Aggregations

Data Normalization

Clearing Aggregations

Truncating aggregations

Minimizing Drops

10.  Actions and Subroutines

11.  Buffers and Buffering

12.  Output Formatting

13.  Speculative Tracing

14.  dtrace(1M) Utility

15.  Scripting

16.  Options and Tunables

17.  dtrace Provider

18.  lockstat Provider

19.  profile Provider

20.  fbt Provider

21.  syscall Provider

22.  sdt Provider

23.  sysinfo Provider

24.  vminfo Provider

25.  proc Provider

26.  sched Provider

27.  io Provider

28.  mib Provider

29.  fpuinfo Provider

30.  pid Provider

31.  plockstat Provider

32.  fasttrap Provider

33.  User Process Tracing

34.  Statically Defined Tracing for User Applications

35.  Security

36.  Anonymous Tracing

37.  Postmortem Tracing

38.  Performance Considerations

39.  Stability

40.  Translators

41.  Versioning



Clearing Aggregations

When using DTrace to build simple monitoring scripts, you can periodically clear the values in an aggregation using the clear() function. This function takes an aggregation as its only parameter. The clear() function clears only the aggregation's values; the aggregation's keys are retained. Therefore, the presence of a key in an aggregation that has an associated value of zero indicates that the key had a non-zero value that was subsequently set to zero as part of a clear(). To discard both an aggregation's values and its keys, use the trunc(). See Truncating aggregations for details.

The following example adds clear() to Example 9-1:

#pragma D option quiet

    last = timestamp;

    @func[execname] = count();

    normalize(@func, (timestamp - last) / 1000000000);
    last = timestamp;

While Example 9-1 shows the system call rate over the lifetime of the dtrace invocation, the preceding example shows the system call rate only for the most recent ten-second period.