Section 7.4. Unaccounted-for Time

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7.4 Unaccounted-for Time

Virtually every trace file you'll ever analyze will have some mismatch between actual response time and the amount of time that the Oracle kernel accounts for in its trace file. Sometimes there will be an under-counting of time, and sometimes there will be an over-counting of time. For reasons you'll understand shortly, under-counting is more common than over-counting. In this book, I refer to both situations as unaccounted-for time . When there's missing time, there is a positive unaccounted-for duration. When there is an over-counting of time, there is a negative unaccounted-for duration. Unaccounted-for time in Oracle trace files can be caused by five distinct phenomena:

• Measurement intrusion effect

• CPU consumption double-counting

• Quantization error

• Time spent not executing

• Un-instrumented Oracle kernel code

I'll discuss each of these contributors of unaccounted-for time in the following sections.

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