Computing devices may synchronize respective copies of a repository in part by sharing status information for records stored in the repository. Status information may be conveyed by encoding record identifiers in a hashtable. A hash function may be selected to have an output range equal to or larger than a number of records in the repository. A plurality of hash function outputs may be mapped to a storage location containing a sum of identifiers and a count of identifiers included in the sum. The storage location may be transmitted to a remote computing device, which may unfold the data in the storage location to identify changed records.