The subject technology receives, by a proxy interface, the request to determine the read version of the transaction. The subject technology determines, based on the request, that the transaction is associated with the tag included in the request. The subject technology generates a sequence number for the request. The subject technology places the request in a queue associated with the tag based on the sequence number, the queue including a set of requests to determine a particular read version of a particular transaction. The subject technology determines, using a token bucket, that the request in the queue should be throttled based on information related to a quota for the tag stored in a distributed database key store.