mysql - I can't tell in which DB a row is located from just the global identifier -

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if have user table (with global id primary key) sharded across 10 databases (db1-db10) based on username, , table tries refer user table using user table row's global id, there no way me know db (1-10) user located in.

what solution problem?

either:

  1. change sharding scheme shard based on key use data. if it's id, id, , shard id (db = id % 10)

  2. make primary key of user table username. enforce uniqueness , use username foreign key in other tables, not synthetic identifier.

  3. create lookup table can reference maps ids shards.


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