A request handler may receive transaction requests for transactions to be executed using data of a database, and may classify a first transaction request of the transaction requests as a simple transaction request, and a second transaction request of the transaction requests as a complex transaction request. A key-value store engine may execute a first transaction satisfying the first transaction request, using a key-value store of pre-calculated results determined prior to receipt of the first transaction request, and based on the data, and may update a key-value delta reflecting a change, if any, of the key-value store caused by the first transaction. A relational store engine may cause the at least one processor to execute a second transaction satisfying the second transaction request, using a relational store including a subset of the data, and may update a relational delta reflecting a change, if any, of the relational store caused by the second transaction. A synchronizer may execute a synchronization of the key-value store and the relational store, based on the key-value delta and the relational delta.