Design and Analysis of a Logless Dynamic Reconfiguration Protocol

Authors William Schultz, Siyuan Zhou, Ian Dardik, Stavros Tripakis

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Author Details

William Schultz
  • Northeastern University, Boston, MA, USA
Siyuan Zhou
  • MongoDB, New York, NY, USA
Ian Dardik
  • Northeastern University, Boston, MA, USA
Stavros Tripakis
  • Northeastern University, Boston, MA,USA


We would like to thank Tess Avitabile for her critical insights during the development of the reconfiguration protocol and discovery of subtle bugs in early design proposals. We would like to thank Judah Schvimer, A. Jesse Jiryu Davis, Pavi Vetriselvan, and Ali Mir for offering helpful insights during the protocol design and implementation process. We would also like to thank Shuai Mu for providing helpful comments on initial drafts of this paper.

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William Schultz, Siyuan Zhou, Ian Dardik, and Stavros Tripakis. Design and Analysis of a Logless Dynamic Reconfiguration Protocol. In 25th International Conference on Principles of Distributed Systems (OPODIS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 217, pp. 26:1-26:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


Distributed replication systems based on the replicated state machine model have become ubiquitous as the foundation of modern database systems. To ensure availability in the presence of faults, these systems must be able to dynamically replace failed nodes with healthy ones via dynamic reconfiguration. MongoDB is a document oriented database with a distributed replication mechanism derived from the Raft protocol. In this paper, we present MongoRaftReconfig, a novel dynamic reconfiguration protocol for the MongoDB replication system. MongoRaftReconfig utilizes a logless approach to managing configuration state and decouples the processing of configuration changes from the main database operation log. The protocol’s design was influenced by engineering constraints faced when attempting to redesign an unsafe, legacy reconfiguration mechanism that existed previously in MongoDB. We provide a safety proof of MongoRaftReconfig, along with a formal specification in TLA+. To our knowledge, this is the first published safety proof and formal specification of a reconfiguration protocol for a Raft-based system. We also present results from model checking the safety properties of MongoRaftReconfig on finite protocol instances. Finally, we discuss the conceptual novelties of MongoRaftReconfig, how it can be understood as an optimized and generalized version of the single server reconfiguration algorithm of Raft, and present an experimental evaluation of how its optimizations can provide performance benefits for reconfigurations.

Subject Classification

ACM Subject Classification
  • Information systems → Parallel and distributed DBMSs
  • Software and its engineering → Software verification
  • Fault Tolerance
  • Dynamic Reconfiguration
  • State Machine Replication


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