[SPARK-21033] fix the potential OOM in UnsafeExternalSorter

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.2.0
• Fix Version/s: 2.3.0
• Component/s: SQL
• Assignee: Wenchen Fan
• Reporter: Wenchen Fan
• Created: 09/Jun/17 08:40
• Updated: 14/May/20 01:38
• Resolved: 30/Oct/17 17:07

Description

In `UnsafeInMemorySorter`, one record may take 32 bytes: 1 `long` for pointer, 1 `long` for key-prefix, and another 2 `long`s as the temporary buffer for radix sort.

In `UnsafeExternalSorter`, we set the `DEFAULT_NUM_ELEMENTS_FOR_SPILL_THRESHOLD` to be `1024 * 1024 * 1024 / 2`, and hoping the max size of point array to be 8 GB. However this is wrong, `1024 * 1024 * 1024 / 2 * 32` is actually 16 GB, and if we grow the point array before reach this limitation, we may hit the max-page-size error.

Users may see exception like this on large dataset:

Caused by: java.lang.IllegalArgumentException: Cannot allocate a page with more than 17179869176 bytes
at org.apache.spark.memory.TaskMemoryManager.allocatePage(TaskMemoryManager.java:241)
at org.apache.spark.memory.MemoryConsumer.allocatePage(MemoryConsumer.java:121)
at org.apache.spark.util.collection.unsafe.sort.UnsafeExternalSorter.acquireNewPageIfNecessary(UnsafeExternalSorter.java:374)
at org.apache.spark.util.collection.unsafe.sort.UnsafeExternalSorter.insertRecord(UnsafeExternalSorter.java:396)
at org.apache.spark.sql.execution.UnsafeExternalRowSorter.insertRow(UnsafeExternalRowSorter.java:94)
...

Issue Links

• is duplicated by: SPARK-22438 OutOfMemoryError on very small data sets
• links to: [Github] Pull Request #18251 (cloud-fan)
• links to: [Github] Pull Request #21077 (wangyum)