FollowStatsIT#testFollowStatsApiIncludeShardFollowStatsWithRemovedFollowerIndex failure

[martijnvg]

[2019-02-11T23:27:48,513][INFO ][o.e.c.m.MetaDataDeleteIndexService] [node_s_0] [leader1/CauqUnDjRpivCn8-gN51hQ] deleting index
FAILURE 0.49s J6 | FollowStatsIT.testFollowStatsApiIncludeShardFollowStatsWithRemovedFollowerIndex <<< FAILURES!
   > Throwable #1: java.lang.AssertionError: 
   > Expected: <1>
   >      but: was <0>
   >    at __randomizedtesting.SeedInfo.seed([A9F2E2FB2B3232F2:982741CACE61265E]:0)
   >    at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
   >    at org.elasticsearch.xpack.ccr.FollowStatsIT.testFollowStatsApiIncludeShardFollowStatsWithRemovedFollowerIndex(FollowStatsIT.java:182)
   >    at java.lang.Thread.run(Thread.java:748)

Build url: https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+g1gc/355/console

[elasticmachine]

Pinging @elastic/es-distributed

[martijnvg]

I found the following NPE in the log, that I think is causing this test failure:

[2019-02-11T23:27:48,452][WARN ][o.e.p.PersistentTasksNodeService] [node_s_0] task kD8YzUhHTK6uKNBNQI-1ZQ-0 failed with an exception
  1> java.lang.NullPointerException: null
  1>    at org.elasticsearch.xpack.ccr.action.ShardFollowTasksExecutor.lambda$fetchFollowerShardInfo$7(ShardFollowTasksExecutor.java:305) ~[main/:?]
  1>    at org.elasticsearch.action.ActionListener$1.onResponse(ActionListener.java:61) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.TransportAction$1.onResponse(TransportAction.java:68) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.TransportAction$1.onResponse(TransportAction.java:64) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.broadcast.node.TransportBroadcastByNodeAction$AsyncAction.onCompletion(TransportBroadcastByNodeAction.java:383) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.broadcast.node.TransportBroadcastByNodeAction$AsyncAction.onNodeResponse(TransportBroadcastByNodeAction.java:352) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.broadcast.node.TransportBroadcastByNodeAction$AsyncAction$1.handleResponse(TransportBroadcastByNodeAction.java:324) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.broadcast.node.TransportBroadcastByNodeAction$AsyncAction$1.handleResponse(TransportBroadcastByNodeAction.java:314) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.transport.TransportService$ContextRestoreResponseHandler.handleResponse(TransportService.java:1108) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.transport.TransportService$DirectResponseChannel.processResponse(TransportService.java:1189) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.transport.TransportService$DirectResponseChannel.sendResponse(TransportService.java:1169) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.transport.TaskTransportChannel.sendResponse(TaskTransportChannel.java:54) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.broadcast.node.TransportBroadcastByNodeAction$BroadcastByNodeTransportRequestHandler.messageReceived(TransportBroadcastByNodeAction.java:417) [elasticsearch-8.0.0-SNAP
SHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.action.support.broadcast.node.TransportBroadcastByNodeAction$BroadcastByNodeTransportRequestHandler.messageReceived(TransportBroadcastByNodeAction.java:391) [elasticsearch-8.0.0-SNAP
SHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.transport.RequestHandlerRegistry.processMessageReceived(RequestHandlerRegistry.java:63) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.transport.TransportService$7.doRun(TransportService.java:687) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:751) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) [elasticsearch-8.0.0-SNAPSHOT.jar:8.0.0-SNAPSHOT]
  1>    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_202]
  1>    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_202]
  1>    at java.lang.Thread.run(Thread.java:748) [?:1.8.0_202]

Index stats response has no commit stats and the ShardFollowTasksExecutor#fetchFollowerShardInfo() method expects that to be there, which causes the NPE. The other consequence of this NPE is that the shard follow persistent task does not get assigned. The test expects shard follow stats, but because no shard follow task got assigned, that assertion fails.

[martijnvg]

Another instance of this failure with the same NPE in the logs: https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+7.0+release-tests/25/console