Implementing Data Replication in Memgraph

In the v1.3 release, Memgraph introduced data replication, a new feature designed to enhance data availability and consistency across distributed systems. The implementation of this feature was challenging due to the need to integrate replication into an existing system without major alterations. Memgraph's replication allows instances to take on MAIN or REPLICA roles, with various modes—SYNC, ASYNC, and SYNC WITH TIMEOUT—offering different balances of the CAP theorem's properties: consistency, availability, and partition tolerance. The system uses transaction timestamps and durability files for synchronization, employing a file retainer to prevent the premature deletion of files critical for replication. Timing issues and the need for efficient file handling were addressed using custom threading solutions and unique identifiers to maintain data integrity across instances. Extensive testing, including simulations using the Jepsen library, ensured robustness by exposing edge cases and validating system behavior under stress. While the current replication feature marks significant progress, Memgraph plans to introduce additional functionalities to further refine its capabilities.