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Oracle® Solaris 11.4 DTrace (Dynamic Tracing) Guide

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Updated: September 2020
 
 

Committing a Speculation

You commit speculations using the commit() function. When a speculative buffer is committed, its data is copied into the principal buffer. If there is more data in the specified speculative buffer than there is available space in the principal buffer, no data is copied and the drop count for the buffer is incremented. If the buffer has been speculatively traced to on more than one CPU, the speculative data on the committing CPU is copied immediately, while speculative data on other CPUs is copied some time after the commit(). Thus, some time might elapse between a commit() beginning on one CPU and the data being copied from speculative buffers to principal buffers on all CPUs. This time is guaranteed to be no longer than the time dictated by the cleaning rate. See Speculation Options and Tuning for more details.

A committing speculative buffer will not be made available to subsequent speculation() calls until each per-CPU speculative buffer has been completely copied into its corresponding per-CPU principal buffer. Similarly, subsequent calls to speculate() to the committing buffer will be silently discarded, and subsequent calls to commit() or discard() will silently fail. Finally, a clause containing a commit() cannot contain a data recording action, but a clause may contain multiple commit() calls to commit disjoint buffers.