Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/18843#discussion_r132146376
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/ExternalAppendOnlyUnsafeRowArray.scala
---
@@ -31,16 +31,16 @@ import org.apache.spark.storage.BlockManager
import org.apache.spark.util.collection.unsafe.sort.{UnsafeExternalSorter,
UnsafeSorterIterator}
/**
- * An append-only array for [[UnsafeRow]]s that spills content to disk
when there a predefined
- * threshold of rows is reached.
+ * An append-only array for [[UnsafeRow]]s that strictly keeps content in
an in-memory array
+ * until [[numRowsInMemoryBufferThreshold]] is reached post which it will
switch to a mode which
+ * would flush to disk after [[numRowsSpillThreshold]] is met (or before
if there is
+ * excessive memory consumption). Setting these threshold involves
following trade-offs:
*
- * Setting spill threshold faces following trade-off:
- *
- * - If the spill threshold is too high, the in-memory array may occupy
more memory than is
- * available, resulting in OOM.
- * - If the spill threshold is too low, we spill frequently and incur
unnecessary disk writes.
- * This may lead to a performance regression compared to the normal case
of using an
- * [[ArrayBuffer]] or [[Array]].
+ * - If [[numRowsSpillThreshold]] is too high, the in-memory array may
occupy more memory than
--- End diff --
typo? this should be `numRowsInMemoryBufferThreshold`. We may spill before
reaching `numRowsSpillThreshold` if memory is not enough.
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