Github user kiszk commented on a diff in the pull request:
https://github.com/apache/spark/pull/18543#discussion_r127763486
--- Diff:
sql/catalyst/src/main/java/org/apache/spark/sql/execution/UnsafeExternalRowSorter.java
---
@@ -211,7 +211,10 @@ public int compare(Object baseObj1, long baseOff1,
Object baseObj2, long baseOff
// TODO: Why are the sizes -1?
row1.pointTo(baseObj1, baseOff1, -1);
row2.pointTo(baseObj2, baseOff2, -1);
- return ordering.compare(row1, row2);
+ int comparison = ordering.compare(row1, row2);
+ row1.pointTo(null, 0L, -1);
+ row2.pointTo(null, 0L, -1);
--- End diff --
@cloud-fan @srowen It is good idea to do this cleanup once at the end. I am
curious how to implement this cleanup.
While @srowen proposed to use `nsafeExternalSorter.cleanupResources` and
`UnsafeInMemorySorter.free` that will be called when a task is finished, to do
cleanup here does not seem to work in this case. This is because [this
issue](https://issues.apache.org/jira/browse/SPARK-21319) occurs before
completing a task since `UnsafeExternalSorter` instance is registered into the
task `taskContext` at
[here](https://github.com/apache/spark/blob/master/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java#L159-L161).
This cleanup approach will not be performed before an OOM occurs during
execution of the task.
IIUC, the end of sort is
[here](https://github.com/apache/spark/blob/master/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeInMemorySorter.java#L345).
This line calls [this sort
method](https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/util/collection/Sorter.scala#L36).
Either to do the cleanup at the first part or to do the cleanup after checking
type of a given comparator at the second part could work.
What do you think?
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