This here will go horribly wrong (endless retry loop) unless the retryable succeeds on its first attempt.

b := &client.Batch{}
b.Put(key, "test")

s.db.Txn(func(txn *client.Txn) error {
        return txn.CommitInBatch(b)
})

Instead, the batch needs to be initialized inside of the retryable (or the error stored within it cleared manually). I ran into this in WIP and took me a bit to track it down. We should reset errors in an appropriate location so that the above isn't a death trap.