PolarDB-X Standard Edition uses distributed technology to deliver a fully centralized experience. Each data node (DN) operates independently and is 100% compatible with MySQL 5.7 and MySQL 8.0, making it a suitable substitute for open-source MySQL with higher availability and stronger transaction guarantees.
Architecture overview
PolarDB-X Standard Edition uses a three-layer architecture. Each layer has a distinct responsibility:
| Layer | Role |
|---|---|
| Log layer | Replication and durability |
| Storage layer | Transaction processing |
| Execution layer | SQL execution and client access |
Log layer
The log layer implements a majority-based replication protocol based on Paxos. Consensus logs are compatible with MySQL binary logs, so existing tooling that relies on binary logs continues to work.
Unlike MySQL source-replica replication — whether asynchronous or semisynchronous — Paxos requires a majority of nodes to acknowledge each write before it succeeds. This guarantees zero data loss in the event of a data center failure, achieving a recovery point objective (RPO) of 0 without any application changes.
Storage layer
The storage layer runs the in-house Lizard transaction system, which interfaces with the log layer and replaces the standalone InnoDB transaction system of MySQL.
Lizard includes two transaction subsystems optimized for different workloads:
| Subsystem | Optimized for |
|---|---|
| SCN standalone transaction system | Centralized transactions on a single node |
| GCN distributed transaction system | Transactions across multiple data nodes |
Transaction isolation levels are fully compatible with MySQL standards, so applications require no changes when migrating from native MySQL.
Execution layer
The execution layer mirrors the server layer in native MySQL, providing SQL parsing, query optimization, and execution. Applications connect and run queries without modification.
The in-house xRPC server extends this layer to support distributed queries when accessing PolarDB-X Enterprise Edition. The execution layer works with the storage layer transaction systems to process data consistently across nodes.
Open source
PolarDB-X Standard Edition was open-sourced in 2023. The source code is available at PolarDB-X Engine.