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From "Paul Rogers (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-5386) Rationalize Drill's use of the Java assertions flag
Date Sat, 25 Mar 2017 21:27:41 GMT
Paul Rogers created DRILL-5386:

             Summary: Rationalize Drill's use of the Java assertions flag
                 Key: DRILL-5386
                 URL: https://issues.apache.org/jira/browse/DRILL-5386
             Project: Apache Drill
          Issue Type: Improvement
    Affects Versions: 1.10.0
            Reporter: Paul Rogers
            Assignee: Paul Rogers
             Fix For: 1.11.0

Java provides a very handy debugging tool: assertions:

assert someInvariantCondition;

Basically, this says that {{someInvariantCondition}} should always hold. This is a quick and
easy way to validate invariants in the code.

Assertions add overhead. To address this concern, assertions are a runtime option, and are
off by default. Assertions are enabled with the {{-ea}} JVM command-line option. When off,
the JVM does not evaluate the assertion, it is as if the assertion were not even in the code.

Although assertions are well-known tools, it seems that Drill went off into two directions
that compromise the usefulness of assertions.

First, Drill uses the {{-ea}} flag to enable other, far more expensive, debugging aids as
well. When assertions are enabled, the allocator performs very expensive checks and logging
on each allocation and deallocation, vastly slowing execution. Second, assertions control
the fault injection mechanism.

Second, since Drill has made assertions so expensive, they are not often used. Instead, Drill
uses Guava preconditions. But, these are always enabled and entail one or more function calls:
much more expensive at run time than assertions.

To address this state of affairs:

* Detach allocator debugging from assertions. Use a config option to enable the allocator
debug features. This avoids the current huge overhead of enabling assertions.
* Similarly, use a config option to enable the fault injection mechanism so faults can be
injected when Drill runs at full performance.
* Encourage the use of Java assertions liberally in new code to allow the JVM to catch bugs
so engineers don't have to do quite so much manual testing.
* Over time, replace Guava preconditions with Java assertions to get Drill to follow normal
Java practices.

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