[Bug]: Flaky Spanner Integration test due to "Could not initialize class com.google.spanner.v1.Session$LabelsDefault"

[Abacn]

Related Template(s)

Spanner templates

Template Version

N/A

What happened?

Spanner PR is flaky, integration test job failed launch. Example error:

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java.lang.NoClassDefFoundError: Could not initialize class com.google.spanner.v1.Session$LabelsDefaultEntryHolder
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at com.google.spanner.v1.Session.internalGetLabels(Session.java:147)
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at com.google.spanner.v1.Session.getSerializedSize(Session.java:490)
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at com.google.protobuf.CodedOutputStream.computeMessageSizeNoTag(CodedOutputStream.java:861)
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at com.google.protobuf.CodedOutputStream.computeMessageSize(CodedOutputStream.java:641)
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at com.google.spanner.v1.BatchCreateSessionsRequest.getSerializedSize(BatchCreateSessionsRequest.java:232)
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at io.grpc.protobuf.lite.ProtoInputStream.available(ProtoInputStream.java:108)
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at io.grpc.internal.MessageFramer.getKnownLength(MessageFramer.java:204)
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at io.grpc.internal.MessageFramer.writePayload(MessageFramer.java:139)
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at io.grpc.internal.AbstractStream.writeMessage(AbstractStream.java:66)
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at io.grpc.internal.ForwardingClientStream.writeMessage(ForwardingClientStream.java:37)
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at io.grpc.internal.DelayedStream$6.run(DelayedStream.java:282)
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at io.grpc.internal.DelayedStream.drainPendingCalls(DelayedStream.java:182)
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at io.grpc.internal.DelayedStream.access$100(DelayedStream.java:44)
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at io.grpc.internal.DelayedStream$4.run(DelayedStream.java:148)
...
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Caused by: java.lang.ExceptionInInitializerError: Exception java.lang.ExceptionInInitializerError [in thread "grpc-default-executor-0"]
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at com.google.spanner.v1.Session$LabelsDefaultEntryHolder.<clinit>(Session.java:132)

different tests failed same reason each time. See #2177 for example.

Relevant log output

[darshan-sj]

NoClassDef found should happen everytime the same tests are run. I don't understand why this is flaky.

Is there any difference between the way we run the tests in the Java PR workflow and Spanner PR workflow?

The Spanner PR continues workflow has one flaky test SpannerToSourceDbCustomTransformationIT which we are working on.

Example: https://github.com/GoogleCloudPlatform/DataflowTemplates/actions/runs/13307357883/job/37161942486
https://github.com/GoogleCloudPlatform/DataflowTemplates/actions/workflows/spanner-pr.yml?query=branch%3Amain

[Abacn]

Thanks for the comment.

NoClassDef found should happen everytime the same tests are run. I don't understand why this is flaky.

NoClassDef could also happen when the static initializer fails, in this case it is in com.google.spanner.v1.Session$LabelsDefaultEntryHolder, there is a static block

static {
      defaultEntry = MapEntry.newDefaultInstance(...);
    }

likely failed