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From "Paul Rogers (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-5612) Random failure in TestMergeJoinWithSchemaChanges
Date Tue, 27 Jun 2017 23:58:00 GMT
Paul Rogers created DRILL-5612:

             Summary: Random failure in TestMergeJoinWithSchemaChanges
                 Key: DRILL-5612
                 URL: https://issues.apache.org/jira/browse/DRILL-5612
             Project: Apache Drill
          Issue Type: Bug
    Affects Versions: 1.11.0
            Reporter: Paul Rogers

The unit test {{org.apache.drill.exec.physical.impl.join.TestMergeJoinWithSchemaChanges#testMissingAndNewColumns}}
is subject to random failures, perhaps due to changes in file order in readers.

The test builds a number of input files, then executes queries against them. On most runs,
the output is fine:

Running org.apache.drill.exec.physical.impl.join.TestMergeJoinWithSchemaChanges#testMissingAndNewColumns

But, on occasion, the query fails:

 Time elapsed: 0.569 sec  <<< ERROR!
...: UNSUPPORTED_OPERATION ERROR: Sort doesn't currently support sorts with changing schemas

Fragment 0:0

  (org.apache.drill.exec.exception.SchemaChangeException) Sort currently only supports a single

The line in the exception above:

  public void build(VectorContainer outputContainer) throws SchemaChangeException {
    if (batches.keySet().size() > 1) {
      throw new SchemaChangeException("Sort currently only supports a single schema.");

The above code has not changed in quite some time. The failure is in the "legacy" external

Although the external sort does support schema changes, it only does so in the form of a union
vector, which must be enabled. (Other tests validate that schema changes work.)

What is likely happening here is that the sort sometimes sees two files with differing schemas,
sometimes multiple threads run so that a single sort sees only one file. This speculation
can be verified by looking at a log file (not available in the test run that failed) to see
if the scan under the sort read more than one file.

Or, perhaps the order of the JSON files matters. Perhaps file order varies across machines
(since the Linux command to list directories does not guarantee order.)

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