Github user ericl commented on a diff in the pull request:
https://github.com/apache/spark/pull/12490#discussion_r60327131
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/execution/UnsafeKVExternalSorter.java
---
@@ -85,13 +85,15 @@ public UnsafeKVExternalSorter(
recordComparator,
prefixComparator,
/* initialSize */ 4096,
- pageSizeBytes);
+ pageSizeBytes,
+ keySchema.length() == 1 &&
SortPrefixUtils.canSortFullyWithPrefix(keySchema.apply(0)));
} else {
// During spilling, the array in map will not be used, so we can
borrow that and use it
// as the underline array for in-memory sorter (it's always large
enough).
// Since we will not grow the array, it's fine to pass `null` as
consumer.
final UnsafeInMemorySorter inMemSorter = new UnsafeInMemorySorter(
- null, taskMemoryManager, recordComparator, prefixComparator,
map.getArray());
+ null, taskMemoryManager, recordComparator, prefixComparator,
map.getArray(),
+ false /* TODO(ekl) is there enough existing memory to do radix
sort here? */);
--- End diff --
So we hit this case when `BytesToBytesMap` is unable to acquire more memory
for rehashing. In this situation we can never use radix sort, since the default
load factor of `BytesToBytesMap` is 0.75.
One possibility is to decrease the `BytesToBytesMap` load factor used by
`TungstenAggregate` to 0.5. Thoughts?
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