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Trace Duration in -ve


Trace Duration in -ve

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yuvipoy
yuvipoy
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Will the SQL server profiler trace duration value will be in -ve?

here is the one i got
Duration Starttime Endtime
-43 2014-05-06 22:26:07.887 2014-05-06 22:26:07.843

how it is possible??
Grant Fritchey
Grant Fritchey
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What do you mean by "-ve"?

And you're right, a negative duration is not really possible. The actual capture of trace events is in microseconds and the GUI in Profiler displays in milliseconds. I have seen that conversion lead to problems. You can change the Profiler GUI to work with microseconds in the options.

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yuvipoy
yuvipoy
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-ve --> negative.I got the negative value in one of my statement.
If you see the duration which i have provided is in milliseconds and thats too 43 millisecond.
Grant Fritchey
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So, it's probably a rounding error. The capture of events in trace is in microseconds. Your display is milliseconds.

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Greg Edwards-268690
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Probably a rounding error.
Could also be server synching time with domain controller, if this happened between start and end of trace.
yuvipoy
yuvipoy
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Grant Fritchey (5/7/2014)
So, it's probably a rounding error. The capture of events in trace is in microseconds. Your display is milliseconds.


Then how to rely on it ?
GilaMonster
GilaMonster
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SQL doesn't use high-precision timers (too resource intensive). Inaccuracy in the order of a few ms is not a problem. Like most rounding issues, the large numbers are accurate enough and a couple ms here or there is not going to skew performance tests, because you should take multiple tests and average.

Gail Shaw
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Grant Fritchey
Grant Fritchey
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Everything Gail said, plus, remember it does capture the values in microseconds. Just change the display to use those instead of milliseconds and you'll see fewer issues.

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The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood...
Theodore Roosevelt

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Author of: SQL Server Query Performance Tuning and SQL Server Execution Plans
Product Evangelist for Red Gate Software
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