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Architecture and Module Structure

Three-Tier Architecture

1. Client Layer

  • Gremlin/Cypher query interfaces
  • REST API endpoints
  • Multiple client language bindings

2. Server Layer (hugegraph-server)

  • REST API Layer (hugegraph-api): GraphAPI, SchemaAPI, GremlinAPI, CypherAPI, AuthAPI
  • Graph Engine Layer (hugegraph-core): Schema management, traversal optimization, task scheduling
  • Backend Interface: Abstraction over storage backends

3. Storage Layer

  • Pluggable backend implementations
  • Each backend extends hugegraph-core abstractions
  • Implements BackendStore interface

Multi-Module Structure

The project consists of 7 main modules:

1. hugegraph-server (13 submodules)

Core graph engine, REST APIs, and backend implementations:

  • hugegraph-core - Core graph engine and abstractions
  • hugegraph-api - REST API implementations (includes OpenCypher in opencypher/)
  • hugegraph-dist - Distribution packaging and scripts
  • hugegraph-test - Test suites (unit, core, API, TinkerPop)
  • hugegraph-example - Example code
  • Backend implementations:
    • hugegraph-rocksdb (default)
    • hugegraph-hstore (distributed)
    • hugegraph-hbase
    • hugegraph-mysql
    • hugegraph-postgresql
    • hugegraph-cassandra
    • hugegraph-scylladb
    • hugegraph-palo

2. hugegraph-pd (8 submodules)

Placement Driver for distributed deployments (meta server):

  • hg-pd-core - Core PD logic
  • hg-pd-service - PD service implementation
  • hg-pd-client - Client library
  • hg-pd-common - Shared utilities
  • hg-pd-grpc - gRPC protocol definitions (auto-generated)
  • hg-pd-cli - Command line interface
  • hg-pd-dist - Distribution packaging
  • hg-pd-test - Test suite

3. hugegraph-store (9 submodules)

Distributed storage backend with RocksDB and Raft:

  • hg-store-core - Core storage logic
  • hg-store-node - Storage node implementation
  • hg-store-client - Client library
  • hg-store-common - Shared utilities
  • hg-store-grpc - gRPC protocol definitions (auto-generated)
  • hg-store-rocksdb - RocksDB integration
  • hg-store-cli - Command line interface
  • hg-store-dist - Distribution packaging
  • hg-store-test - Test suite

4. hugegraph-commons

Shared utilities across modules:

  • Locks and concurrency utilities
  • Configuration management
  • RPC framework components

5. hugegraph-struct

Data structure definitions shared between modules. Important: Must be built before PD and Store modules.

6. install-dist

Distribution packaging and release management:

  • License and NOTICE files
  • Dependency management scripts
  • Release documentation

7. hugegraph-cluster-test

Cluster integration tests for distributed deployments

Cross-Module Dependencies

hugegraph-commons → (shared by all modules)
hugegraph-struct → hugegraph-pd + hugegraph-store
hugegraph-core → (extended by all backend implementations)

Distributed Architecture (Optional)

For production distributed deployments:

  • hugegraph-pd: Service discovery, partition management, metadata
  • hugegraph-store: Distributed storage with Raft (3+ nodes)
  • hugegraph-server: Multiple server instances (3+)
  • Communication: All use gRPC with Protocol Buffers

Status: Distributed components (PD + Store) are in BETA