Details
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Bug
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Status: Reopened
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Not a Priority
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Resolution: Unresolved
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None
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None
Description
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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