MOCHIKABU
Architecture

Published on 2022-02-28 • 12 Min Read

Legacy Database Modernization: Moving to Distributed SQL

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Traditional database architectures rely on active-passive replication to manage failures. If the primary database fails, a manual or automated failover is triggered. This introduces synchronization lag, potential data loss (RPO > 0), and significant downtime (RTO > 0). Distributed SQL solves this constraint by design.

Active-Active Synchronous Replication

Distributed SQL databases utilize consensus protocols (such as Raft or Paxos) to replicate data synchronously across multiple independent cloud regions. Every database node is active and capable of handling write transactions.

Moving away from classic active-passive database architectures to distributed SQL engines requires redesigning data models for optimal sharding. Because data is distributed across multiple nodes, selecting the right shard keys is vital to avoid hot spots and minimize cross-region network latency during transactions.

Multi-Region Distributed SQLRegion A (Frankfurt)Active NodeRegion B (Dublin)Active NodeRegion C (Zurich)Active NodeSynchronous Raft Replication

Key Benefits of Distributed SQL

  • Zero Data Loss (RPO = 0): Synchronous consensus ensures transactions are committed across multiple regions simultaneously.
  • Near-Instant Failover (RTO < 5s): Automatic leadership re-election in case of regional outages without manual intervention.
  • Horizontal Scale: Read and write scaling by adding nodes without database partitioning.

The Mechanics of Raft Consensus

At the heart of Distributed SQL is consensus. Instead of relying on a single master database to write and mirror data asynchronously, a write transaction must be accepted by a majority (quorum) of database nodes before it is committed. This guarantees complete consistency even during sudden network splits.

Distributed SQL Resilience Pillars

A modern distributed SQL database relies on decentralized replication and consensus layers to ensure high availability and transaction consistency.

Distributed ResiliencyActive-Active SyncRaft ConsensusMulti-Region FailoverStrict Serializability
Raft Consensus Quorum VotingLeaderFollower 1Follower 21. Replicate2. ACK1. Replicate2. ACKQuorum Achieved (2 of 3 nodes acknowledged) -> Commit Successful

Migrating Core Financial Systems

For transactional systems such as core banking, the migration to Distributed SQL provides unprecedented resiliency. Regional cloud outages no longer cause transaction failures, ensuring continuous service availability for end-users while simplifying multi-region engineering.

Moving from active-passive to distributed SQL is less a database swap than a resilience upgrade. The payoff is operational continuity across regions, but only if the consistency model is understood and tested, not assumed.

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