Hi, In the Javadoc for Combine.GroupedValues[1], it has been described that *combining the values associated with a single key can happen in parallel*. The logic to combine values associated with a key can be provided by CombineFnWithContext (or) CombineFn. Both CombineFnWithContext.apply()[2] and CombineFn.apply()[3] uses a single accumulator to combine the values.
My understanding is that the parallelism in Combine PTransform will be determined by the no. of accumulators. But, the Javadoc describes that combining is done in parallel even though the no. of accumulators used to combine is one. How can combine happen parallelly by using only one accumulator? Regards, Rahul [1]: https://github.com/apache/beam/blob/334682d4a8ac5e1ebd298ba3b8020a9161884927/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java#L2075-L2078 [2]: https://github.com/apache/beam/blob/53e5cee254023152e77a3fc46564642dc9b6b506/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/CombineWithContext.java#L117 [3]: https://github.com/apache/beam/blob/334682d4a8ac5e1ebd298ba3b8020a9161884927/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java#L443
