With the transmission of enormous data from multiple channels, the issues are rising related to big data and associated performance of storage engines on cloud environment. These datasets and signals are getting transmitted on assorted domains including social media, live streaming of multimedia, satellites, Internet of Things (IoT) based monitoring and many others. To process and execute such huge data, there is need to incorporate specialized and high performance database engines because of concurrency, integrity and security issues. The traditional relational database systems are not effective in handling such heterogeneous as well as big data flowing on cloud. From last few years, the advent of NoSQL databases attempts to provide a secured and high performance system using which millions of database queries per second can be processed. Even, these database systems can handle unstructured data in multiple formats without any compatibility issues. There are more than hundred NoSQL databases which are prominently used in different applications. In this research manuscript, the evaluation of two database systems MongoDB and Cassandra is done on query execution time to evaluate the relative performance with the pragmatic analysis. From the results, it is found that Cassandra NoSQL is quite effectual in terms of minimum execution time as compared to MongoDB with the excellent powers towards throughput with high write and no downtime.