JacobZheng created SPARK-47146:
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Summary: Possible thread leak when doing sort merge join
Key: SPARK-47146
URL: https://issues.apache.org/jira/browse/SPARK-47146
Project: Spark
Issue Type: Bug
Components: Spark Core
Affects Versions: 3.4.0, 3.3.0, 3.2.0
Reporter: JacobZheng
I have a long-running spark job. stumbled upon executor taking up a lot of
threads, resulting in no threads available on the server. Querying thread
details via jstack, there are tons of threads named read-ahead. Checking the
code confirms that these threads are created by ReadAheadInputStream. This
class is initialized to create a single-threaded thread pool
{code:java}
private final ExecutorService executorService =
ThreadUtils.newDaemonSingleThreadExecutor("read-ahead"); {code}
This thread pool is closed by ReadAheadInputStream#close().
The call stack for the normal case close() method is
{code:java}
ts=2024-02-21 17:36:18;thread_name=Executor task launch worker for task 60.0 in
stage 71.0 (TID
258);id=330;is_daemon=true;priority=5;TCCL=org.apache.spark.util.MutableURLClassLoader@17233230
@org.apache.spark.io.ReadAheadInputStream.close()
at
org.apache.spark.util.collection.unsafe.sort.UnsafeSorterSpillReader.close(UnsafeSorterSpillReader.java:149)
at
org.apache.spark.util.collection.unsafe.sort.UnsafeSorterSpillReader.loadNext(UnsafeSorterSpillReader.java:121)
at
org.apache.spark.util.collection.unsafe.sort.UnsafeSorterSpillMerger$1.loadNext(UnsafeSorterSpillMerger.java:87)
at
org.apache.spark.sql.execution.UnsafeExternalRowSorter$1.advanceNext(UnsafeExternalRowSorter.java:187)
at
org.apache.spark.sql.execution.RowIteratorToScala.hasNext(RowIterator.scala:67)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage27.processNext(null:-1)
at
org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43)
at
org.apache.spark.sql.execution.WholeStageCodegenExec$$anon$1.hasNext(WholeStageCodegenExec.scala:760)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage29.smj_findNextJoinRows_0$(null:-1)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage29.hashAgg_doAggregateWithKeys_1$(null:-1)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage29.hashAgg_doAggregateWithKeys_0$(null:-1)
at
org.apache.spark.sql.catalyst.expressions.GeneratedClass$GeneratedIteratorForCodegenStage29.processNext(null:-1)
at
org.apache.spark.sql.execution.BufferedRowIterator.hasNext(BufferedRowIterator.java:43)
at
org.apache.spark.sql.execution.WholeStageCodegenExec$$anon$2.hasNext(WholeStageCodegenExec.scala:779)
at scala.collection.Iterator$$anon$10.hasNext(Iterator.scala:460)
at
org.apache.spark.shuffle.sort.BypassMergeSortShuffleWriter.write(BypassMergeSortShuffleWriter.java:140)
at
org.apache.spark.shuffle.ShuffleWriteProcessor.write(ShuffleWriteProcessor.scala:59)
at
org.apache.spark.scheduler.ShuffleMapTask.runTask(ShuffleMapTask.scala:101)
at
org.apache.spark.scheduler.ShuffleMapTask.runTask(ShuffleMapTask.scala:53)
at
org.apache.spark.TaskContext.runTaskWithListeners(TaskContext.scala:161)
at org.apache.spark.scheduler.Task.run(Task.scala:139)
at
org.apache.spark.executor.Executor$TaskRunner.$anonfun$run$3(Executor.scala:554)
at org.apache.spark.util.Utils$.tryWithSafeFinally(Utils.scala:1529)
at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:557)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.lang.Thread.run(Thread.java:829) {code}
As shown in UnsafeSorterSpillReader#close, the stream is only closed when the
data in the stream is read through.
{code:java}
@Override
public void loadNext() throws IOException {
// Kill the task in case it has been marked as killed. This logic is from
// InterruptibleIterator, but we inline it here instead of wrapping the
iterator in order
// to avoid performance overhead. This check is added here in `loadNext()`
instead of in
// `hasNext()` because it's technically possible for the caller to be relying
on
// `getNumRecords()` instead of `hasNext()` to know when to stop.
if (taskContext != null) {
taskContext.killTaskIfInterrupted();
}
recordLength = din.readInt();
keyPrefix = din.readLong();
if (recordLength > arr.length) {
arr = new byte[recordLength];
baseObject = arr;
}
ByteStreams.readFully(in, arr, 0, recordLength);
numRecordsRemaining--;
if (numRecordsRemaining == 0) {
close();
}
} {code}
In sort merge join+inner join, if any StreamSide or BufferSide iterator touches
the end, the unread iterator at the other end will not continue to read. A
similar situation exists for left and right outer joins.
In short, in several specific sort merge join types, a memory leak can occur
when the amount of data is so large that a spill is triggered and there are
iterators that are not read through.
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