Tom van Bussel created SPARK-32901:
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Summary: UnsafeExternalSorter may cause a SparkOutOfMemoryError to
be thrown while spilling
Key: SPARK-32901
URL: https://issues.apache.org/jira/browse/SPARK-32901
Project: Spark
Issue Type: Bug
Components: Spark Core
Affects Versions: 3.0.1, 2.4.7
Reporter: Tom van Bussel
Consider the following sequence of events:
# {{UnsafeExternalSorter}} runs out of space in its pointer array and attempts
to allocate a large array to replace the current one.
# {{TaskMemoryManager}} tries to allocate the memory backing the large array
using {{MemoryManager}}, but {{MemoryManager}} is only willing to return most
but not all of the memory requested.
# {{TaskMemoryManager}} asks {{UnsafeExternalSorter}} to spill, which causes
{{UnsafeExternalSorter}} to spill the current run to disk, to free its record
pages and to reset its {{UnsafeInMemorySorter}}.
# {{UnsafeInMemorySorter}} frees its pointer array, and tries to allocate a
new small pointer array.
# {{TaskMemoryManager}} tries to allocate the memory backing the small array
using {{MemoryManager}}, but {{MemoryManager}} is unwilling to give it any
memory, as the {{TaskMemoryManager}} is still holding on to the memory it got
for the large array.
# {{TaskMemoryManager}} again asks {{UnsafeExternalSorter}} to spill, but this
time there is nothing to spill.
# {{UnsafeInMemorySorter}} receives less memory than it requested, and causes
a {{SparkOutOfMemoryError}} to be thrown, which causes the current task to fail.
A simple way to fix this is to avoid allocating a new array in
{{UnsafeInMemorySorter.reset()}} and to do this on-demand instead.
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