Load Balance Writes in Cluster

I was wondering how Xtradb handles multiple writes in cluster. If you have auto-increments or created users with ids on same table how does it handle that? Would there be multiple same ids if 2 different writes happen at same time on different nodes? I am sure they have worked out something smart about it but how reliable it really is?

Galera, so library used in Percona XtraDB Cluster, by default sets different pools of auto increment values for each node, so no conflict possible for simple inserts. For more complicated cases there are mechanisms to avoid and resolve conflicts.
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