We decompose 64 bit ids to shard_id, type and local_id. We connect to the shard go to the table and read the local_id. We randomly select a shard for a new use

We decompose 64 bit ids to shard_id, type and local_id. We connect to the shard go to the table and read the local_id. We randomly select a shard for a new user only. Ofcourse we capacity plan this and open new shards and even out users eventually.