For the MongoDB linkbench POC, the applyOps command was used to emulate transactions, but, for document updates within an applyOps command, there is no support for querying a document by anything other than it's _id field, even if the query would uniquely identify a document. This seems like a restriction that shouldn't be present for multi-statement transactions. Once transactional updates support querying unique documents by non _id fields, we should change the schema of the Link documents and Count documents, so they don't have to awkwardly concatenate their unique fields for their _id. Removing the concatenated _id should make the benchmark more analogous to the MySQL schema used for its benchmark.