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https://issues.apache.org/jira/browse/CASSANDRA-14156?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16558641#comment-16558641
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Jason Brown commented on CASSANDRA-14156:
-----------------------------------------
I was able to repro the flakey fail after 17 runs on my laptop. With
[~krummas]'s patch, it ran 50 times without fail.
The [debug
statement|https://github.com/krummas/cassandra-dtest/commit/42e9125c189f61dd31a2fc0a157b95e6ecea4cf1#diff-376c5cd8425c9b4b078f87a20db738b9R300]
in the patch should be removed as it fails hard with the following error:
{noformat}
test_movement failed and was not selected for rerun.
<class 'NameError'>
name 'debug' is not defined
[<TracebackEntry
/opt/orig/1/opt/dev/cassandra-dtest/topology_test.py:300>]
{noformat}
As it's not essential, you can probably remove it. Otherwise, +1.
> [DTEST] [TRUNK] TestTopology.movement_test is flaky; fails assert "values not
> within 16.00% of the max: (851.41, 713.26)"
> -------------------------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-14156
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14156
> Project: Cassandra
> Issue Type: Bug
> Components: Testing
> Reporter: Michael Kjellman
> Assignee: Marcus Eriksson
> Priority: Major
> Labels: dtest
>
> DTest* TestTopology.test_movement* is flaky. All of the testing so far (and
> thus all of the current known observed failures) have been when running
> against trunk. When the test fails, it always due to the assert_almost_equal
> assert.
> {code}
> AssertionError: values not within 16.00% of the max: (851.41, 713.26) ()
> {code}
> The following CircleCI runs are 2 examples with dtests runs that failed due
> to this test failing it's assert:
> [https://circleci.com/gh/mkjellman/cassandra/487]
> [https://circleci.com/gh/mkjellman/cassandra/526]
> *p.s.* assert_almost_equal has a comment "@params error Optional margin of
> error. Default 0.16". I don't see any obvious notes for why the default is
> this magical 16% number. It looks like it was committed as part of a big bulk
> commit by Sean McCarthy (who I can't find on JIRA). If anyone has any history
> on the magic 16% allowed delta please share!
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