OutOfMemory error while merging in AppenderatorImpl

[jihoonson]

AppenderatorImpl currently merges all persisted indexes at once. This can incur OOM error like below if there are too many indexes to be merged when longEncoding = auto .

2018-09-13T23:33:55,073 ERROR [task-runner-0-priority-0] io.druid.indexing.common.task.IndexTask - Encountered exception in BUILD_SEGMENTS.
java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.OutOfMemoryError: Java heap space
        at com.google.common.base.Throwables.propagate(Throwables.java:160) ~[guava-16.0.1.jar:?]
        at io.druid.indexing.common.task.IndexTask.generateAndPublishSegments(IndexTask.java:1042) ~[druid-indexing-service-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.indexing.common.task.IndexTask.run(IndexTask.java:455) [druid-indexing-service-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.indexing.overlord.ThreadPoolTaskRunner$ThreadPoolTaskRunnerCallable.call(ThreadPoolTaskRunner.java:457) [druid-indexing-service-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.indexing.overlord.ThreadPoolTaskRunner$ThreadPoolTaskRunnerCallable.call(ThreadPoolTaskRunner.java:429) [druid-indexing-service-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_161]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_161]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_161]
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_161]
Caused by: java.util.concurrent.ExecutionException: java.lang.OutOfMemoryError: Java heap space
        at com.google.common.util.concurrent.AbstractFuture$Sync.getValue(AbstractFuture.java:299) ~[guava-16.0.1.jar:?]
        at com.google.common.util.concurrent.AbstractFuture$Sync.get(AbstractFuture.java:286) ~[guava-16.0.1.jar:?]
        at com.google.common.util.concurrent.AbstractFuture.get(AbstractFuture.java:116) ~[guava-16.0.1.jar:?]
        at io.druid.segment.realtime.appenderator.BatchAppenderatorDriver.pushAndClear(BatchAppenderatorDriver.java:141) ~[druid-server-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.realtime.appenderator.BatchAppenderatorDriver.pushAllAndClear(BatchAppenderatorDriver.java:124) ~[druid-server-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.indexing.common.task.IndexTask.generateAndPublishSegments(IndexTask.java:1004) ~[druid-indexing-service-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        ... 7 more
Caused by: java.lang.OutOfMemoryError: Java heap space
        at it.unimi.dsi.fastutil.longs.LongArrays.grow(LongArrays.java:222) ~[fastutil-8.1.0.jar:?]
        at it.unimi.dsi.fastutil.longs.LongArrayList.grow(LongArrayList.java:277) ~[fastutil-8.1.0.jar:?]
        at it.unimi.dsi.fastutil.longs.LongArrayList.add(LongArrayList.java:296) ~[fastutil-8.1.0.jar:?]
        at io.druid.segment.data.IntermediateColumnarLongsSerializer.add(IntermediateColumnarLongsSerializer.java:89) ~[druid-processing-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.LongColumnSerializer.serialize(LongColumnSerializer.java:87) ~[druid-processing-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.IndexMergerV9.mergeIndexesAndWriteColumns(IndexMergerV9.java:458) ~[druid-processing-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.IndexMergerV9.makeIndexFiles(IndexMergerV9.java:209) ~[druid-processing-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.IndexMergerV9.merge(IndexMergerV9.java:837) ~[druid-processing-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.IndexMergerV9.mergeQueryableIndex(IndexMergerV9.java:710) ~[druid-processing-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.IndexMergerV9.mergeQueryableIndex(IndexMergerV9.java:688) ~[druid-processing-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.realtime.appenderator.AppenderatorImpl.mergeAndPush(AppenderatorImpl.java:662) ~[druid-server-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.realtime.appenderator.AppenderatorImpl.lambda$push$0(AppenderatorImpl.java:566) ~[druid-server-0.12.2-iap7-SNAPSHOT.jar:0.12.2-iap7-SNAPSHOT]
        at io.druid.segment.realtime.appenderator.AppenderatorImpl$$Lambda$117/371981722.apply(Unknown Source) ~[?:?]
        at com.google.common.util.concurrent.Futures$1.apply(Futures.java:713) ~[guava-16.0.1.jar:?]
        at com.google.common.util.concurrent.Futures$ChainingListenableFuture.run(Futures.java:861) ~[guava-16.0.1.jar:?]
        ... 3 more

[b-slim]

I am not sure why this issue is called a bug, can you please elaborate more? IMO this works as expected unless you can determine exactly upfront how much memory left to be allocated and you know exactly the size of the input data.

[jihoonson]

Alright. Maybe it makes more sense to call improvement.

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