Risingwave

RisingWave

RisingWave is a streaming SQL database implementing the PostgreSQL wire protocol. The core pipeline is: Source (ingest) → Materialized View (continuous compute) → Sink (output).

Core Principles

1. Port 4566, not 5432 — RisingWave listens on 4566 for SQL connections. Dashboard is at 5691.
2. SOURCE ≠ TABLE — CREATE SOURCE connects a stream but doesn't persist data. CREATE TABLE persists. For CDC (Debezium, Maxwell, Canal), you MUST use CREATE TABLE ... FROM source.
3. Watermarks unlock window closing — Without WATERMARK FOR col AS col - INTERVAL '...', EMIT ON WINDOW CLOSE won't work; use it on the source or table definition. In RisingWave 2.8+, watermarks on TABLE require APPEND ONLY — use CREATE SOURCE for non-append-only streams that need watermarks.
4. EMIT ON WINDOW CLOSE vs default — Default emit-on-update sends partial results after each checkpoint. Use EMIT ON WINDOW CLOSE for final, immutable window results.
5. Large backfills need BACKGROUND_DDL — Creating an MV over a large table blocks without SET BACKGROUND_DDL = true. Monitor with SELECT * FROM rw_catalog.rw_ddl_progress.
6. snapshot = false on sinks — Adding a sink to an existing MV without this flag replays all historical data into the sink.
7. Verify docs — RisingWave evolves rapidly. When unsure, check docs.risingwave.com or query SHOW CREATE on existing objects.

Connection

# Default local connection
psql -h localhost -p 4566 -d dev -U root

# Docker (single-node)
docker run -it --pull=always -p 4566:4566 -p 5691:5691 \
  risingwavelabs/risingwave:latest single_node

Connection string: postgresql://root:@localhost:4566/dev

Any PostgreSQL-compatible client works: psql, JDBC, psycopg2, pgx, SQLAlchemy, dbt, Grafana.

MCP Server Setup

RisingWave has an official MCP server with 100+ tools (query execution, schema exploration, streaming job monitoring, CDC progress, Kafka lag, Hummock storage analysis).

git clone https://github.com/risingwavelabs/risingwave-mcp.git
cd risingwave-mcp && pip install -r requirements.txt

Configure via environment variable:

RISINGWAVE_CONNECTION_STR=postgresql://root:@localhost:4566/dev

Add to your agent's MCP config (Claude Code: ~/.claude/claude_desktop_config.json, VS Code: .vscode/mcp.json):

{
  "mcpServers": {
    "risingwave": {
      "type": "stdio",
      "command": "python",
      "args": ["/path/to/risingwave-mcp/src/main.py"],
      "env": {
        "RISINGWAVE_CONNECTION_STR": "postgresql://root:@localhost:4566/dev"
      }
    }
  }
}

The Pipeline Pattern

Stream data → SOURCE → MATERIALIZED VIEW(s) → SINK(s)
Static/CDC data → TABLE ─────────────────────────────╯

Step 1: Source (streaming, no persistence)

CREATE SOURCE user_events (
    user_id     INT,
    action      VARCHAR,
    event_time  TIMESTAMP,
    WATERMARK FOR event_time AS event_time - INTERVAL '5 SECOND'
)
WITH (
    connector = 'kafka',
    topic = 'user-events',
    properties.bootstrap.server = 'kafka:9092',
    scan.startup.mode = 'latest'
)
FORMAT PLAIN ENCODE JSON;

Step 2: Materialized View (continuous compute)

-- Windowed aggregation with final results on window close
CREATE MATERIALIZED VIEW active_users_per_minute AS
SELECT
    action,
    COUNT(DISTINCT user_id) AS unique_users,
    window_start,
    window_end
FROM TUMBLE(user_events, event_time, INTERVAL '1 MINUTE')
GROUP BY action, window_start, window_end
EMIT ON WINDOW CLOSE;

-- Plain aggregation (emit on every update)
CREATE MATERIALIZED VIEW user_action_counts AS
SELECT user_id, action, COUNT(*) AS cnt
FROM user_events
GROUP BY user_id, action;

Step 3: Sink (output)

CREATE SINK alerts_to_kafka FROM active_users_per_minute
WITH (
    connector = 'kafka',
    topic = 'user-alerts',
    properties.bootstrap.server = 'kafka:9092',
    snapshot = false   -- skip historical backfill
)
FORMAT PLAIN ENCODE JSON;

CDC Pattern (Database Replication)

CDC requires a two-step setup: shared connection source + per-table TABLE.

-- Step 1: shared CDC source connection
CREATE SOURCE pg_cdc WITH (
    connector = 'postgres-cdc',
    hostname = 'postgres-host',
    port = '5432',
    username = 'replicator',
    password = '<your-password>',
    database.name = 'mydb',
    slot.name = 'rw_slot'
);

-- Step 2: per-table ingestion (TABLE, not SOURCE)
CREATE TABLE orders (
    id          INT PRIMARY KEY,
    customer_id INT,
    total       DECIMAL,
    created_at  TIMESTAMP
)
FROM pg_cdc TABLE 'public.orders';

Time Windows

All three window types add window_start and window_end columns.

-- TUMBLE: non-overlapping fixed windows
FROM TUMBLE(table, time_col, INTERVAL '5 MINUTES')

-- HOP (sliding): overlapping windows
-- hop_size = slide interval, window_size = total duration
FROM HOP(table, time_col, INTERVAL '1 MINUTE', INTERVAL '5 MINUTES')

Note: SESSION windows are only supported in batch mode in RisingWave 2.x. For streaming, use TUMBLE or HOP.

Pattern: Always group by window_start, window_end and add EMIT ON WINDOW CLOSE when using watermarks.

Useful System Catalog Queries

-- All materialized views with definitions
SELECT name, definition FROM rw_catalog.rw_materialized_views;

-- DDL progress during MV creation / backfill
SELECT ddl_id, ddl_statement, progress FROM rw_catalog.rw_ddl_progress;

-- Active sources and their connectors
SELECT name, connector FROM rw_catalog.rw_sources;

-- Sink info
SELECT name, sink_type, connector FROM rw_catalog.rw_sinks;

-- CDC backfill progress
SELECT job_id, split_total_count, split_backfilled_count, split_completed_count
FROM rw_catalog.rw_cdc_progress;

-- Cluster nodes
SELECT id, host, type, state FROM rw_catalog.rw_worker_nodes;

-- Inspect object definition
SHOW CREATE MATERIALIZED VIEW my_mv;
SHOW CREATE SOURCE my_source;
SHOW CREATE SINK my_sink;

Useful Session Settings

-- Large backfills: non-blocking DDL
SET BACKGROUND_DDL = true;

-- Share Kafka source across multiple MVs (v2.1+)
SET streaming_use_shared_source = true;

Troubleshooting

MCP server not connecting

• Verify RISINGWAVE_CONNECTION_STR is set and RisingWave is running on port 4566
• Test the connection first: psql -h localhost -p 4566 -d dev -U root
• Check Python version: python --version (requires Python 3.8+)

EMIT ON WINDOW CLOSE produces no output

• The source or table must have WATERMARK FOR col AS col - INTERVAL '...' defined
• Confirm watermark is advancing: insert rows with recent timestamps, not historical data
• Check MV definition: SHOW CREATE MATERIALIZED VIEW my_mv

MV creation hangs / session times out

• Use SET BACKGROUND_DDL = true before CREATE MATERIALIZED VIEW
• Monitor progress: SELECT ddl_id, ddl_statement, progress FROM rw_catalog.rw_ddl_progress

CDC table not receiving updates

• Verify PostgreSQL has wal_level = logical and the replication user has REPLICATION role
• Check CDC lag: SELECT * FROM rw_catalog.rw_cdc_progress
• Ensure slot.name in CREATE SOURCE is unique and does not already exist on the upstream DB

Sink sending duplicate historical data

• Add snapshot = false to the sink WITH clause to skip backfilling existing MV data

References

• Connectors reference — all supported sources and sinks
• System catalog reference — full rw_catalog table listing
• RisingWave docs
• RisingWave MCP server