# A Performance Evaluation of In-Memory Databases Operations in Session Initiation Protocol
## 4 Related Works  
Key-value cache systems have been studied and analyzed in several fields. Web servers have engaged in this evaluation as key-value cache systems are widely involved in such fields. Meanwhile, a number of research activities have been conducted for benchmarks and evaluation.  
The work of [26] examined different NoSQL databases and evaluated their performance based on data storage and retrieval. In this work, a YCSB tool had been utilized to measure the performance of three names of databases which are MongoDB, Cassandra, and Redis. The authors found that MongoDB finally has a superior performance with the NoSQL database over Redis and Cassandra. MongoDB has significantly decreased the latency factor for all operation counts. The authors of [27] provided a comparative study between three solutions widely employed: Cassandra, Redis, and MongoDB by testing the run-time of read, update, scan, and read-modify-write operations. In summary, their results show that, with read and write operations, Redis outperforms other databases due to the use of volatile memory to store and retrieve data. On other hand, MongoDB performs with higher efficiency in the read operations than Cassandra due to the registers mapping technique of MongoDB, which helps increase read performance. In an empirical comparison study between Aerospike, Memcached, and Redis analyzed in [28],the work aimed to present a comparison using variant workloads (read-heavy, balanced, and write-heavy). The research was conducted based on a multiple-client scenario and configured Memcached with two thread connections. The authors found that Memcached had the best performance over others due to the caching layer technique that has been used in read-heavy and balanced scenarios. In [29], the authors have examined five names of database systems in the field of health enterprises, and they have evaluated operation completion time and memory efficiency. The results showed that no winner database provides the best performance for all data operations. The authors in [30] have provided a benchmark on Yahoo! Cloud Serving with NoSQL database performance by applying 600,000 records in different workloads. The authors have evaluated five database names including Redis, HBase, Cassandra, OrientDB8, and MongoDB. They reported that Redis provides the best performance over others' column family databases, while HBase and Cassandra reported better update performance. The author of [31] had implemented a custom list data type in Memcached over Redis in the web industry, and the main finding of the thesis is that (1) Redis has superior performance with a small data size of the list and (2) when data size increases, Redis performance decreases. (3) Horizontal scalability in Memcached had better performance over Redis for a list of large data sizes. The work in [32] has examined four MySQL database machines according to access modes by the SIP server, and the authors analyzed the performance based on system recovery delay, registration response time, and processing delay. They also found that the response time is short in memory-only mode, and the response time of the write-back mode is the same as in memory-only mode. However, the write-through mode consumes extra time over memory-only mode.  
At the time of writing, there are no studies or benchmarks completed in the field of SIP and NoSQL databases. In fact, the NoSQL database has gained wide consideration in the field of web industries and research, but not in SIP.