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https://issues.apache.org/jira/browse/FLINK-16386?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17051956#comment-17051956
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Stephan Ewen commented on FLINK-16386:
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If a test assumes deterministic iteration order, but the production code gives
no such guaranteed, then the test should be adjusted, not the production code.
Unless the production code claims to give deterministic iteration order.
> Use LinkedHashMap in SqlFunctionUtils.java
> ------------------------------------------
>
> Key: FLINK-16386
> URL: https://issues.apache.org/jira/browse/FLINK-16386
> Project: Flink
> Issue Type: Bug
> Components: Table SQL / Runtime
> Reporter: cpugputpu
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 20m
> Remaining Estimate: 0h
>
> The test in
> _org.apache.flink.table.planner.expressions.ScalarFunctionsTest#testStringToMap_
> can fail due to a different iteration order of a HashMap. The failure is
> presented as follows.
> _org.junit.ComparisonFailure: Wrong result for: [STR_TO_MAP(f46)] optimized
> to:[STR_TO_MAP($46)]
> expected:<\{test1=1, test2=2, test3=3}> but was:<\{test2=2, test1=1,
> test3=3}>_
> The root cause of this issue lies in a HashMap initialized in
> SqlFunctionUtils.java, which makes no guarantee about the iteration order. A
> brief stack trace of the HashMap's iterator is presented here:
> _java.util.HashMap$EntrySet.iterator(HashMap.java:1014)
> org.apache.flink.table.dataformat.DataFormatConverters$MapConverter.toBinaryMap(DataFormatConverters.java:1174)
> org.apache.flink.table.dataformat.DataFormatConverters$MapConverter.toInternalImpl(DataFormatConverters.java:1157)
> org.apache.flink.table.dataformat.DataFormatConverters$MapConverter.toInternalImpl(DataFormatConverters.java:1114)
> org.apache.flink.table.dataformat.DataFormatConverters$DataFormatConverter.toInternal(DataFormatConverters.java:290)
> TestFunction$144.map(Unknown_ Source)
> org.apache.flink.table.planner.expressions.utils.ExpressionTestBase.evaluateExprs(ExpressionTestBase.scala:152)
> The specification about HashMap says that "this class makes no guarantees as
> to the order of the map; in particular, it does not guarantee that the order
> will remain constant over time". The documentation is here for your
> reference: [https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html]
> The fix is to use LinkedHashMap instead of HashMap. In this way, the test
> will not suffer from failure any more and the code will be more stable, free
> of this non-deterministic behaviour.
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