Hello, Right now, if someone needs sharded files via FileIO, there is only one option which is random (round robin) shard assignment per element and it always use ShardedKey<Integer> as a key for the GBK which follows.
I would like to generalize this and have a possibility to provide some ShardingFn[UserT, DestinationT, ShardKeyT] via FileIO. What I am mainly after is, to have a possibility to provide optimisation for Flink runtime and pass in a special function which generates shard keys in a way that they are evenly spread among workers (BEAM-5865). Would such extension for FileIO make sense? If yes, I would create a ticket for it and try to draft a PR. Best, Jozef
