chore: remove legacy backends

.serena/memories/architecture_and_modules.md

@@ -5,19 +5,19 @@
 ### 1. Client Layer
 - Gremlin/Cypher queries, REST APIs, Swagger UI
 
-### 2. Server Layer (hugegraph-server, 13 submodules)
+### 2. Server Layer (hugegraph-server, 8 submodules)
 - **REST API** (hugegraph-api): GraphAPI, SchemaAPI, GremlinAPI, CypherAPI, AuthAPI, GraphSpaceAPI (distributed only), ManagerAPI (distributed only)
 - **Graph Engine** (hugegraph-core): Schema (with TTL update), traversal, task scheduling, GraphSpace multi-tenancy
 - **Backend Interface**: Pluggable via `BackendStore`
 
 ### 3. Storage Layer
 - RocksDB (default/embedded), HStore (distributed/production)
-- Legacy (≤1.5.0, deprecated, excluded from context): MySQL, PostgreSQL, Cassandra, ScyllaDB, HBase, Palo
+- HBase (deprecated; planned for removal in 2.0)
 
 ## Module Structure (7 top-level modules)
 
-### hugegraph-server (13 submodules)
-`hugegraph-core`, `hugegraph-api` (includes `opencypher/`, `space/`), `hugegraph-dist`, `hugegraph-test`, `hugegraph-example`, plus backends: `hugegraph-rocksdb`, `hugegraph-hstore`, `hugegraph-hbase`, `hugegraph-mysql`, `hugegraph-postgresql`, `hugegraph-cassandra`, `hugegraph-scylladb`, `hugegraph-palo`
+### hugegraph-server (8 submodules)
+`hugegraph-core`, `hugegraph-api` (includes `opencypher/`, `space/`), `hugegraph-dist`, `hugegraph-test`, `hugegraph-example`, plus backends: `hugegraph-rocksdb`, `hugegraph-hstore`, `hugegraph-hbase`
 
 ### hugegraph-pd (8 submodules)
 Placement Driver: `hg-pd-core`, `hg-pd-service`, `hg-pd-client`, `hg-pd-common`, `hg-pd-grpc`, `hg-pd-cli`, `hg-pd-dist`, `hg-pd-test`

.serena/memories/implementation_patterns_and_guidelines.md

@@ -4,8 +4,7 @@
 - Backends implement `BackendStore` interface from `hugegraph-core`
 - Each backend = separate Maven module under `hugegraph-server/`
 - Configured via `hugegraph.properties` → `backend` property
-- **Active backends (focus here)**: RocksDB (default/embedded), HStore (distributed)
-- **Legacy backends** (deprecated, excluded from Serena context): MySQL, PostgreSQL, Cassandra, ScyllaDB, HBase, Palo
+- **Supported backends**: RocksDB (default/embedded), HStore (distributed), HBase (deprecated; planned for removal in 2.0)
 
 ## GraphSpace Multi-Tenancy
 - Core: `hugegraph-core/.../space/` (GraphSpace, SchemaTemplate, Service, register/)

.serena/memories/project_overview.md

@@ -19,8 +19,7 @@ Apache HugeGraph is a fast-speed, highly-scalable graph database supporting 10+
 - **Graph Framework**: Apache TinkerPop 3.5.1
 - **RPC**: gRPC + Protocol Buffers
 - **API Docs**: Swagger (io.swagger.core.v3)
-- **Storage**: RocksDB (default/embedded), HStore (distributed/production)
-- **Legacy backends** (≤1.5.0): MySQL, PostgreSQL, Cassandra, ScyllaDB, HBase, Palo
+- **Storage**: RocksDB (default/embedded), HStore (distributed/production), HBase (deprecated; planned for removal in 2.0)
 
 ## Version
 - Current: 1.7.0 (`${revision}` property, Maven flatten plugin)

.serena/project.yml

@@ -35,12 +35,7 @@ ignore_all_files_in_gitignore: true
 # Same syntax as gitignore, so you can use * and **.
 # Note: global ignored_paths from serena_config.yml are also applied additively.
 ignored_paths:
-  # --- Deprecated backends (focus on RocksDB/HStore only) ---
-  - "hugegraph-server/hugegraph-cassandra/**"
-  - "hugegraph-server/hugegraph-scylladb/**"
-  - "hugegraph-server/hugegraph-mysql/**"
-  - "hugegraph-server/hugegraph-postgresql/**"
-  - "hugegraph-server/hugegraph-palo/**"
+  # --- HBase is deprecated and planned for removal in 2.0 ---
   - "hugegraph-server/hugegraph-hbase/**"
   # --- gRPC generated Java (235k lines, never hand-edited, regenerated by mvn compile) ---
   - "hugegraph-pd/hg-pd-grpc/src/main/java/**"

README.md

@@ -31,7 +31,7 @@ achieved through the powerful [Gremlin](https://tinkerpop.apache.org/gremlin.htm
 
 - **Schema Metadata Management**: VertexLabel, EdgeLabel, PropertyKey, and IndexLabel
 - **Multi-type Indexes**: Exact query, range query, and complex conditions combination query
-- **Plug-in Backend Store Framework**: Mainly supports `RocksDB`/`HStore` + `HBase`; other backends available in [legacy versions](https://hugegraph.apache.org/docs/download/download/) ≤ `1.5.0` (MySQL/PostgreSQL/Cassandra...)
+- **Plug-in Backend Store Framework**: Since `1.7.0`, supported backends are `RocksDB`, `HStore`, `HBase`, and `Memory`. Historical versions earlier than `1.7.0` also supported MySQL, PostgreSQL, Cassandra, ScyllaDB, and Palo.
 - **Big Data Integration**: Seamless integration with `Flink`/`Spark`/`HDFS`
 - **Complete Graph Ecosystem**: In/out-memory Graph Computing + Graph Visualization & Tools + Graph Learning & AI
 - **Dual Query Language Support**: [Gremlin](https://tinkerpop.apache.org/gremlin.html) (via [Apache TinkerPop 3](https://tinkerpop.apache.org/)) and [Cypher](https://en.wikipedia.org/wiki/Cypher_(query_language)) (OpenCypher)
@@ -78,11 +78,11 @@ HugeGraph supports both **standalone** and **distributed** deployments:
              ┌────────────────────────────────┼────────────────────────────────┐
              │                                │                                │
 ┌────────────▼────────────┐   ┌───────────────▼───────────────┐   ┌───────────▼──────────┐
-│    Standalone Mode      │   │      Distributed Mode         │   │   Legacy Backends    │
-│  ┌───────────────────┐  │   │  ┌─────────────────────────┐  │   │      (≤v1.5)         │
-│  │      RocksDB      │  │   │  │     HugeGraph-PD        │  │   │  MySQL │ PostgreSQL  │
-│  │    (embedded)     │  │   │  │   (Raft, 3-5 nodes)     │  │   │  Cassandra           │
-│  └───────────────────┘  │   │  │      :8620/:8686        │  │   │  HBase (≤v1.7)       │
+│    Standalone Mode      │   │      Distributed Mode         │   │  Supported Backends  │
+│  ┌───────────────────┐  │   │  ┌─────────────────────────┐  │   │  RocksDB │ Memory    │
+│  │      RocksDB      │  │   │  │     HugeGraph-PD        │  │   │  HBase   │ HStore    │
+│  │    (embedded)     │  │   │  │   (Raft, 3-5 nodes)     │  │   │                    │
+│  └───────────────────┘  │   │  │      :8620/:8686        │  │   │                    │
 │                         │   │  └────────────┬────────────┘  │   └──────────────────────┘
 │  Use Case:              │   │               │               │
 │  Development/Testing    │   │  ┌────────────▼────────────┐  │
@@ -148,18 +148,19 @@ flowchart TB
             PD <--> STORE
         end
 
-        subgraph Legacy["Legacy Backends (≤v1.5)"]
-            MYSQL[(MySQL)]
-            PG[(PostgreSQL)]
-            CASS[(Cassandra)]
-            HBASE[(HBase, ≤v1.7)]
+        subgraph Backends["Supported Backends"]
+            HBASE[(HBase)]
+            HSTORE[(HStore)]
+            MEMORY[(Memory)]
         end
     end
 
     Clients --> Server
     CORE --> ROCKS
     CORE --> PD
-    CORE -.-> Legacy
+    CORE --> HBASE
+    CORE --> HSTORE
+    CORE --> MEMORY
 
     style Server fill:#e1f5ff
     style Distributed fill:#fff4e1

docker/hbase/README.md

@@ -158,7 +158,7 @@ After either path is up, run the shared tests below.
 
 - Base URL: `http://localhost:8080`
 - Graph target name: `hugegraph`
-- Storage backend: persistent (HBase/Cassandra/RocksDB)
+- Storage backend: persistent (HBase/RocksDB/HStore)
 
 ---
 

hugegraph-cluster-test/hugegraph-clustertest-test/src/main/resources/jar.txt

@@ -1,14 +1,9 @@
 hugegraph-api-${revision}.jar
-hugegraph-cassandra-${revision}.jar
 hugegraph-common-${revision}.jar
 hugegraph-core-${revision}.jar
 hugegraph-dist-${revision}.jar
 hugegraph-hbase-${revision}.jar
 hugegraph-hstore-${revision}.jar
-hugegraph-mysql-${revision}.jar
-hugegraph-palo-${revision}.jar
-hugegraph-postgresql-${revision}.jar
 hugegraph-rocksdb-${revision}.jar
 hugegraph-rpc-${revision}.jar
-hugegraph-scylladb-${revision}.jar
 hugegraph-struct-${revision}.jar

hugegraph-server/AGENTS.md

@@ -8,7 +8,7 @@ HugeGraph Server is the graph engine layer of Apache HugeGraph, consisting of:
 - **REST API Layer** (hugegraph-api): RESTful APIs for graph operations, Gremlin/Cypher queries, schema management, and authentication
 - **Graph Engine Layer** (hugegraph-core): TinkerPop 3 implementation, schema management, traversal optimization, task scheduling
 - **Backend Interface**: Abstraction layer for pluggable storage backends
-- **Storage Backend Implementations**: RocksDB (default), HStore (distributed), and legacy backends (MySQL, PostgreSQL, Cassandra, ScyllaDB, HBase, Palo)
+- **Storage Backend Implementations**: RocksDB (default), HStore (distributed), HBase, and Memory
 
 Technology: Java 11+, Maven 3.5+, Apache TinkerPop 3.5.1, Jersey 3.0 (REST), gRPC (distributed communication)
 
@@ -50,7 +50,7 @@ mvn checkstyle:check
 - `memory`: In-memory backend (default for tests)
 - `rocksdb`: RocksDB backend
 - `hbase`: HBase backend
-- `mysql`, `postgresql`, `cassandra`, `scylladb`, `palo`: Other backends
+- `hstore`: HStore backend
 
 ```bash
 # Unit tests (from hugegraph-server/)
@@ -78,20 +78,15 @@ All tests are in `hugegraph-test/` which depends on all other modules. Tests are
 
 ## Module Structure
 
-Multi-module Maven project with 13 submodules:
+Multi-module Maven project with 8 submodules:
 
 ```
 hugegraph-server/
 ├── hugegraph-core          # Graph engine, TinkerPop impl, schema, backend interface
 ├── hugegraph-api           # REST API, Gremlin/Cypher endpoints, authentication
 ├── hugegraph-rocksdb       # RocksDB backend (default, embedded)
 ├── hugegraph-hstore        # HStore backend (distributed, production)
-├── hugegraph-mysql         # MySQL backend (legacy)
-├── hugegraph-postgresql    # PostgreSQL backend (legacy)
-├── hugegraph-cassandra     # Cassandra backend (legacy)
-├── hugegraph-scylladb      # ScyllaDB backend (legacy)
-├── hugegraph-hbase         # HBase backend (legacy)
-├── hugegraph-palo          # Palo backend (legacy)
+├── hugegraph-hbase         # HBase backend
 ├── hugegraph-dist          # Distribution packaging, scripts, configs
 ├── hugegraph-test          # All test suites
 └── hugegraph-example       # Example code

hugegraph-server/hugegraph-api/pom.xml

@@ -70,7 +70,7 @@
                     <groupId>com.alipay.sofa</groupId>
                     <artifactId>hessian</artifactId>
                 </exclusion>
-                <!-- conflict with cassandra-netty/tinkerpop-server  -->
+                <!-- avoid netty version conflicts with tinkerpop-server -->
                 <exclusion>
                     <groupId>io.netty</groupId>
                     <artifactId>netty-all</artifactId>