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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-4462) Use System.nanoTime on JDK 1.5 and higher to get finer precision internal measurements
Date Fri, 04 Dec 2009 22:21:20 GMT
Use System.nanoTime on JDK 1.5 and higher to get finer precision internal measurements
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                 Key: DERBY-4462
                 URL: https://issues.apache.org/jira/browse/DERBY-4462
             Project: Derby
          Issue Type: Improvement
          Components: SQL
            Reporter: Bryan Pendleton
            Priority: Minor


Derby uses System.currentTimeMillis() to compute the internal elapsed time of certain operations.
For example, the parseTime, bindTime, optimizeTime, generateTime, and compileTime measurements
that are computed by GenericStatement.prepMinion use this technique.

System.currentTimeMillis is not terribly accurate, since it is only updated 60 times a second;
this
means that it doesn't give very good information about operations that take less than 16 milliseconds,
and the compilation time of a SQL statement is often shorter than that.

As Knut Anders observes, we could use System.nanoTime, which is available in JDK 1.5 and above,
to make more precise measurements.

See DERBY-4297 for some related observations.

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