Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/7849#discussion_r36036068
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/execution/UnsafeFixedWidthAggregationMap.java
---
@@ -225,4 +232,93 @@ public void printPerfMetrics() {
System.out.println("Total memory consumption (bytes): " +
map.getTotalMemoryConsumption());
}
+ /**
+ * Sorts the key, value data in this map in place, and return them as an
iterator.
+ *
+ * The only memory that is allocated is the address/prefix array, 16
bytes per record.
+ */
+ public KVIterator<UnsafeRow, UnsafeRow> sortedIterator() {
+ int numElements = map.numElements();
+ final int numKeyFields = groupingKeySchema.size();
+ TaskMemoryManager memoryManager = map.getTaskMemoryManager();
+
+ UnsafeExternalRowSorter.PrefixComputer prefixComp =
+ SortPrefixUtils.createPrefixGenerator(groupingKeySchema);
+ PrefixComparator prefixComparator =
SortPrefixUtils.getPrefixComparator(groupingKeySchema);
+
+ final BaseOrdering ordering =
GenerateOrdering.create(groupingKeySchema);
+ RecordComparator recordComparator = new RecordComparator() {
+ private final UnsafeRow row1 = new UnsafeRow();
+ private final UnsafeRow row2 = new UnsafeRow();
+
+ @Override
+ public int compare(Object baseObj1, long baseOff1, Object baseObj2,
long baseOff2) {
+ row1.pointTo(baseObj1, baseOff1 + 4, numKeyFields, -1);
+ row2.pointTo(baseObj2, baseOff2 + 4, numKeyFields, -1);
+ return ordering.compare(row1, row2);
+ }
+ };
+
+ // Insert the records into the in-memory sorter.
+ final UnsafeInMemorySorter sorter = new UnsafeInMemorySorter(
+ memoryManager, recordComparator, prefixComparator, numElements);
+
+ BytesToBytesMap.BytesToBytesMapIterator iter = map.iterator();
+ UnsafeRow row = new UnsafeRow();
+ while (iter.hasNext()) {
+ final BytesToBytesMap.Location loc = iter.next();
+ final Object baseObject = loc.getKeyAddress().getBaseObject();
+ final long baseOffset = loc.getKeyAddress().getBaseOffset();
+
+ // Get encoded memory address
+ MemoryBlock page = loc.getMemoryPage();
+ long address = memoryManager.encodePageNumberAndOffset(page,
baseOffset - 8);
--- End diff --
Maybe add a one-line comment here (or at the top of the loop) to explain
that `baseObject` + `baseOffset` point to the beginning of the key data in the
map, but that the KV-pair's length data is stored in the word immediately
before that address.
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