elasticsearch.client.RestClient has 500 error.

When I execute "g.V().has('name', textContains('小米')).limit(10).values('name')" on gremlin-server.
This error happened every morning， in our production environment.

But， I try some times. It can get result.

56919039 [gremlin-server-exec-3] WARN  org.apache.tinkerpop.gremlin.server.handler.HttpGremlinEndpointHandler  - Invalid request - responding with 500 Internal Server Error and listener timeout after waiting for [30000] ms
java.io.IOException: listener timeout after waiting for [30000] ms
	at org.elasticsearch.client.RestClient$SyncResponseListener.get(RestClient.java:661)
	at org.elasticsearch.client.RestClient.performRequest(RestClient.java:220)
	at org.elasticsearch.client.RestClient.performRequest(RestClient.java:192)
	at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.performRequest(RestElasticSearchClient.java:320)
	at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.search(RestElasticSearchClient.java:276)
	at org.janusgraph.diskstorage.es.rest.RestElasticSearchClient.search(RestElasticSearchClient.java:53)
	at org.janusgraph.diskstorage.es.ElasticSearchIndex.query(ElasticSearchIndex.java:926)
	at org.janusgraph.diskstorage.indexing.IndexTransaction.queryStream(IndexTransaction.java:113)
	at org.janusgraph.diskstorage.BackendTransaction$6.call(BackendTransaction.java:417)
	at org.janusgraph.diskstorage.BackendTransaction$6.call(BackendTransaction.java:414)
	at org.janusgraph.diskstorage.util.BackendOperation.executeDirect(BackendOperation.java:69)
	at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:55)
	at org.janusgraph.diskstorage.BackendTransaction.executeRead(BackendTransaction.java:470)
	at org.janusgraph.diskstorage.BackendTransaction.indexQuery(BackendTransaction.java:414)
	at org.janusgraph.graphdb.database.IndexSerializer.query(IndexSerializer.java:548)
	at org.janusgraph.graphdb.util.SubqueryIterator.<init>(SubqueryIterator.java:66)
	at org.janusgraph.graphdb.transaction.StandardJanusGraphTx$6.execute(StandardJanusGraphTx.java:1281)
	at org.janusgraph.graphdb.transaction.StandardJanusGraphTx$6.execute(StandardJanusGraphTx.java:1150)
	at org.janusgraph.graphdb.query.QueryProcessor$LimitAdjustingIterator.getNewIterator(QueryProcessor.java:209)
	at org.janusgraph.graphdb.query.LimitAdjustingIterator.hasNext(LimitAdjustingIterator.java:68)
	at org.janusgraph.graphdb.query.ResultSetIterator.nextInternal(ResultSetIterator.java:54)
	at org.janusgraph.graphdb.query.ResultSetIterator.<init>(ResultSetIterator.java:44)
	at org.janusgraph.graphdb.query.QueryProcessor.iterator(QueryProcessor.java:68)
	at com.google.common.collect.Iterables$7.iterator(Iterables.java:613)
	at org.janusgraph.graphdb.tinkerpop.optimize.JanusGraphStep.lambda$new$0(JanusGraphStep.java:69)
	at org.apache.tinkerpop.gremlin.process.traversal.step.map.GraphStep.processNextStart(GraphStep.java:139)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.hasNext(ExpandableStepIterator.java:42)
	at org.janusgraph.graphdb.tinkerpop.optimize.JanusGraphPropertiesStep.initialize(JanusGraphPropertiesStep.java:87)
	at org.janusgraph.graphdb.tinkerpop.optimize.JanusGraphPropertiesStep.processNextStart(JanusGraphPropertiesStep.java:106)
	at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143)
	at org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversal.hasNext(DefaultTraversal.java:192)
	at org.apache.tinkerpop.gremlin.util.iterator.IteratorUtils.fill(IteratorUtils.java:62)
	at org.apache.tinkerpop.gremlin.util.iterator.IteratorUtils.list(IteratorUtils.java:85)
	at org.apache.tinkerpop.gremlin.util.iterator.IteratorUtils.asList(IteratorUtils.java:382)
	at org.apache.tinkerpop.gremlin.server.handler.HttpGremlinEndpointHandler.lambda$channelRead$1(HttpGremlinEndpointHandler.java:241)
	at org.apache.tinkerpop.gremlin.util.function.FunctionUtils.lambda$wrapFunction$0(FunctionUtils.java:36)
	at org.apache.tinkerpop.gremlin.groovy.engine.GremlinExecutor.lambda$eval$0(GremlinExecutor.java:296)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
	
	
	

Start by reproducing the reported Gremlin traversal and trace the timeout through RestElasticSearchClient.java, ElasticSearchIndex.java, and the Elasticsearch RestClient calls shown in the stack trace. Compare the intermittent 30-second failure with successful requests; done means the cause is confirmed and a reproducible fix or clear conclusion is documented.