Questions about exchangeKind of ExchangeRel

[whutjs]

I am trying to add support in Isthmus for converting Apache Calcite LogicalExchange, as what I described in https://github.com/substrait-io/substrait-java/issues/153. But I run into some problems about how to map the types of exchange from Calcite to Substrait.

In Apache Calcite, there are 6 types of exchange:

1. BROADCAST_DISTRIBUTED;
2. HASH_DISTRIBUTED;
3. RANDOM_DISTRIBUTED;
4. RANGE_DISTRIBUTED;
5. ROUND_ROBIN_DISTRIBUTED;
6. SINGLETON;

In Substrait, there are 5 types of exchange:

1. Scatter;
2. Single Bucket;
3. Multi Bucket;
4. Broadcast;
5. Round Robin;

So my questions are:

• What are single and multi bucket exchanges in Substrait? What are the corresponding exchange types in Calcite?
• Is hash distributed exchange in Calcite corresponding to the scatter exchange in Substrait?

Thanks in advance!