steveniemitz commented on a change in pull request #14852:
URL: https://github.com/apache/beam/pull/14852#discussion_r677746544
##########
File path:
runners/google-cloud-dataflow-java/src/main/java/org/apache/beam/runners/dataflow/GroupIntoBatchesOverride.java
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@@ -87,14 +94,25 @@ private BatchGroupIntoBatches(long batchSize) {
new DoFn<KV<K, Iterable<V>>, KV<K, Iterable<V>>>() {
@ProcessElement
public void process(ProcessContext c) {
- // Iterators.partition lazily creates the partitions as
they are accessed
- // allowing it to partition very large iterators.
- Iterator<List<V>> iterator =
-
Iterators.partition(c.element().getValue().iterator(), (int) batchSize);
-
- // Note that GroupIntoBatches only outputs when the
batch is non-empty.
- while (iterator.hasNext()) {
- c.output(KV.of(c.element().getKey(), iterator.next()));
+ List<V> currentBatch = Lists.newArrayList();
+ long batchSizeBytes = 0;
+ for (V element : c.element().getValue()) {
+ currentBatch.add(element);
+ if (weigher != null) {
+ batchSizeBytes += weigher.apply(element);
+ }
+ if (currentBatch.size() == maxBatchSizeElements
+ || (maxBatchSizeBytes != Long.MAX_VALUE
+ && batchSizeBytes >= maxBatchSizeBytes)) {
+ c.output(KV.of(c.element().getKey(), currentBatch));
+ // Call clear() since that allows us to reuse the
array memory for
+ // subsequent batches.
+ currentBatch.clear();
Review comment:
looking at this, I don't understand how this is safe. Isn't this
mutating an element once it's been emitted? If fused step happens to store this
list somewhere outside of the processElement call (state, buffer between
start/end bundle, etc), it'll be mutated out from under it.
Is there a copy happening somewhere else under the covers that makes this
safe?
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