access-all-partitions pattern not supported in current L2 client

[imzhenyu]

Problem

In our current design, L2 client can only be used to access one specific partition of an application. However, there are usage patterns that requires accessing all partitions in an application, e.g., look up all related document IDs using a keyword when the lookup tables are partitioned by document ID in search.

Solution

We use a special partition-hash (e.g., -1) to represent this requirement from upper application, and L2 client should provide group-address with grpc_to_all as the target. Note grpc-to-all is also not implemented yet.