Querying station/platform resource (expanded) throws Java Heap Space exception

[ridoo]

(moved from 52North/sensorweb-server-helgoland#381)

In the case that there are millions of observations for a series/dataset, the query for a station/resource (expanded) throws a Java Heap Space exception after some time.

It looks like the issue happens when the resultTimes are processed in the DatasetEntity.

Here is the log statement:

18-May-2017 08:20:40.602 SEVERE [http-nio-127.0.0.1-8080-exec-7] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [rest-dispatcher] in context with path [/52n-sos-webapp] threw exception [Request processing failed; nested exception is org.hibernate.PropertyAccessException: Exception occurred inside setter of org.n52.series.db.beans.DatasetEntity.resultTimes] with root cause
 java.lang.OutOfMemoryError: Java heap space
        at java.util.HashMap.newNode(HashMap.java:1742)
        at java.util.HashMap.putVal(HashMap.java:630)
        at java.util.HashMap.put(HashMap.java:611)
        at org.hibernate.collection.internal.PersistentSet.getSnapshot(PersistentSet.java:98)
        at org.hibernate.engine.spi.CollectionEntry.postInitialize(CollectionEntry.java:214)
        at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollection(CollectionLoadContext.java:262)
        at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:238)
        at org.hibernate.engine.loading.internal.CollectionLoadContext.endLoadingCollections(CollectionLoadContext.java:211)
        at org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerImpl.endLoading(CollectionReferenceInitializerImpl.java:168)
        at org.hibernate.loader.plan.exec.process.internal.AbstractRowReader.finishLoadingCollections(AbstractRowReader.java:255)
        at org.hibernate.loader.plan.exec.process.internal.AbstractRowReader.finishUp(AbstractRowReader.java:218)
        at org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl.extractResults(ResultSetProcessorImpl.java:140)
        at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:138)
        at org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad(AbstractLoadPlanBasedLoader.java:102)
        at org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer.initialize(AbstractLoadPlanBasedCollectionInitializer.java:100)
        at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:693)
        at org.hibernate.event.internal.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:92)
        at org.hibernate.internal.SessionImpl.initializeCollection(SessionImpl.java:1933)
        at org.hibernate.collection.internal.AbstractPersistentCollection$4.doWork(AbstractPersistentCollection.java:559)
        at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:261)
        at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:555)
        at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:143)
        at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180)
        at java.util.Spliterators$IteratorSpliterator.estimateSize(Spliterators.java:1821)
        at java.util.Spliterator.getExactSizeIfKnown(Spliterator.java:408)
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:480)
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
        at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
        at org.n52.series.db.beans.DatasetEntity.wrapToUnmutables(DatasetEntity.java:263)
        at org.n52.series.db.beans.DatasetEntity.setResultTimes(DatasetEntity.java:254)