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PostgreSQL Extension for RAFT- Based Leader Election and Cluster Coordination. Background workers, shared memory state, clean C core with Go bridge. PG16+.

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# pgraft

**Raft consensus for distributed PostgreSQL clusters**

[![PostgreSQL](https://img.shields.io/badge/PostgreSQL-14%20%E2%80%93%2018-336791.svg?logo=postgresql&logoColor=white)](https://postgresql.org/)
[![Go](https://img.shields.io/badge/Go-1.21%2B-00ADD8.svg?logo=go&logoColor=white)](https://golang.org/)
[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://raw.githubusercontent.com/pgElephant/pgraft/main/LICENSE)
[![Documentation](https://img.shields.io/badge/docs-GitHub%20Pages-336791.svg)](https://pgelephant.github.io/pgraft/)

[Documentation](https://pgelephant.github.io/pgraft/) ·
[Quick Start](https://pgelephant.github.io/pgraft/getting-started/quick-start/) ·
[Releases](https://github.com/pgelephant/pgraft/releases) ·
[Discussions](https://github.com/pgelephant/pgraft/discussions)

</div>

---

## Overview

**pgraft** is a PostgreSQL extension that brings the [Raft consensus
algorithm](https://raft.github.io/) to distributed PostgreSQL clusters. It
provides automatic leader election, crash-safe log replication, and provable
split-brain prevention, built on the production-grade
[etcd-io/raft](https://github.com/etcd-io/raft) library and integrated through a
native background worker — no external agents or dependencies.

| | Feature | Description |
|---|---|---|
| **Consensus** | Automatic leader election | Quorum-based, deterministic, fully automated |
| **Durability** | Crash-safe replication | State changes replicated and persisted across nodes |
| **Safety** | Split-brain prevention | Guaranteed by the Raft quorum protocol |
| **Availability** | Automatic failover | Sub-second detection and recovery |
| **Integration** | Native PostgreSQL | Background-worker architecture, managed via SQL |
| **Storage** | etcd-compatible KV store | Raft-replicated key/value storage included |
| **Observability** | Status & metrics | Cluster status, replication stats, structured logging |

### Supported platforms

| Platform | PostgreSQL | Status |
|---|---|:---:|
| Linux — RHEL / Rocky / AlmaLinux | 14 – 18 | Supported |
| Linux — Ubuntu / Debian | 14 – 18 | Supported |
| macOS | 14 – 18 | Supported |

> [!NOTE]
> Official release packages are published for PostgreSQL 16, 17, and 18; the
> extension also builds from source on PostgreSQL 14 and 15.

---

## Installation

<details>
<summary>From source</summary>

```bash
# Prerequisites: PostgreSQL 14+, Go 1.21+, json-c, pkg-config
git clone https://github.com/pgelephant/pgraft.git
cd pgraft
make
sudo make install
```

Build against a specific PostgreSQL installation:

```bash
make PG_CONFIG=/usr/pgsql-17/bin/pg_config
sudo make install PG_CONFIG=/usr/pgsql-17/bin/pg_config
```

</details>

<details>
<summary>Pre-built packages</summary>

Download the appropriate package from the
[Releases](https://github.com/pgelephant/pgraft/releases) page.

```bash
# RHEL / Rocky / AlmaLinux
sudo dnf install pgraft_17-1.0.0-1.el9.x86_64.rpm

# Ubuntu / Debian
sudo apt install ./postgresql-17-pgraft_1.0.0-1_amd64.deb
```

</details>

<details>
<summary>Build prerequisites by platform</summary>

```bash
# Ubuntu / Debian
sudo apt update
sudo apt install build-essential postgresql-server-dev-17 golang-go \
                 libjson-c-dev pkg-config git

# RHEL / Rocky / AlmaLinux
sudo dnf install gcc make postgresql17-devel golang json-c-devel \
                 pkg-config git

# macOS
brew install postgresql@17 go json-c pkg-config
```

</details>

> [!TIP]
> See the [complete installation guide](https://pgelephant.github.io/pgraft/getting-started/installation/)
> for detailed, platform-specific instructions.

---

## Configuration

Add the following to `postgresql.conf` on **every** node, adjusting `pgraft.name`
and the addresses per node:

```ini
shared_preload_libraries = 'pgraft'

# Node identity (must be unique and appear in initial_cluster)
pgraft.name = 'node1'

# Cluster membership — identical on all nodes
pgraft.initial_cluster = 'node1=http://10.0.1.11:7001,node2=http://10.0.1.12:7001,node3=http://10.0.1.13:7001'
pgraft.initial_cluster_state = 'new'
pgraft.initial_cluster_token = 'pgraft-cluster-1'

# Local Raft transport endpoint
pgraft.listen_peer_urls = 'http://0.0.0.0:7001'

# Persistent storage for logs, snapshots, and HardState
pgraft.data_dir = '/var/lib/postgresql/pgraft'

# Consensus timing (optional)
pgraft.election_timeout = 1000     # milliseconds
pgraft.heartbeat_interval = 100    # milliseconds
```

> [!IMPORTANT]
> - `pgraft.name` must be unique and match a member name in `pgraft.initial_cluster`.
> - `pgraft.initial_cluster` and `pgraft.initial_cluster_token` must be **identical** on all nodes.
> - Node IDs are assigned automatically from each member's position in `initial_cluster`.
> - Changes to `shared_preload_libraries` require a PostgreSQL restart.

See the [configuration reference](https://pgelephant.github.io/pgraft/user-guide/configuration/)
for the full list of parameters.

---

## Quick start

Create the extension on each node — the cluster forms automatically from the
`initial_cluster` configuration:

```sql
CREATE EXTENSION pgraft;

-- Cluster state, leadership, and membership
SELECT * FROM pgraft_get_cluster_status();
SELECT * FROM pgraft_get_nodes();
```

> [!NOTE]
> Leader election completes within a few seconds of the cluster starting. Query
> `pgraft_get_leader()` to confirm a leader has been elected before issuing
> leader-only operations.

Follow the [quick start guide](https://pgelephant.github.io/pgraft/getting-started/quick-start/)
for a complete walkthrough.

---

## Usage

### Cluster status and health

```sql
SELECT pgraft_is_leader();                        -- is this node the leader?
SELECT pgraft_get_leader();                        -- current leader id
SELECT * FROM pgraft_get_cluster_status();         -- full status
SELECT * FROM pgraft_get_nodes();                  -- all members

SELECT * FROM pgraft_log_get_replication_status(); -- replication progress
SELECT * FROM pgraft_log_get_stats();              -- log statistics
```

### Key/value store (etcd-compatible)

```sql
SELECT pgraft_kv_put('app/config', '{"timeout":30,"retries":3}');  -- leader only
SELECT pgraft_kv_get('app/config');                                -- any node
SELECT pgraft_kv_list_keys();
SELECT pgraft_kv_delete('app/config');                             -- leader only
```

### Dynamic membership

```sql
SELECT pgraft_add_node(4, '10.0.1.14', 7004);   -- leader only
SELECT pgraft_remove_node(4);                     -- leader only
```

> [!WARNING]
> Write operations — `pgraft_kv_put`, `pgraft_kv_delete`, `pgraft_add_node`, and
> `pgraft_remove_node` — must be issued on the **leader**. Guard automated jobs
> with `pgraft_is_leader()` to avoid errors on followers.

See the [SQL function reference](https://pgelephant.github.io/pgraft/user-guide/sql-functions/)
for the complete API.

---

## Architecture

```mermaid
flowchart TD
 subgraph PG["PostgreSQL process"]
 direction TB
 BW["Background worker (C) ticks every 100&nbsp;ms"]
 API["SQL API (C) cluster · status · KV · log"]
 end

BW -->|pgraft_go_tick| GO["Go Raft engine (etcd-io/raft)"]
 API -.->|manage / query| GO

GO --> ELECT["Leader election"]
 GO --> REPL["Log replication"]
 GO --> STORE["Persistent storage logs · snapshots · HardState"]
 GO --> NET["TCP transport"]

NET <-->|Raft RPC| PEERS["Peer nodes"]
```

| Layer | Responsibility |
|---|---|
| **C layer** | PostgreSQL integration, SQL functions, background worker |
| **Go layer** | Raft consensus engine (etcd-io/raft) |
| **Storage** | Durable logs, snapshots, and HardState on disk |
| **Network** | TCP transport for inter-node Raft communication |

The background worker ticks the Raft state machine every 100 ms. The Go engine
handles elections, log replication, and consensus; committed entries are applied
locally on every node, and all state is persisted for crash safety. Management
and monitoring are exposed entirely through SQL.

Further reading:
[architecture](https://pgelephant.github.io/pgraft/concepts/architecture/) ·
[automatic replication](https://pgelephant.github.io/pgraft/concepts/automatic-replication/) ·
[split-brain protection](https://pgelephant.github.io/pgraft/concepts/split-brain/).

---

## Testing with Docker

The `pgraft_cluster.py` helper provisions a multi-node cluster for local testing:

```bash
cd examples

./pgraft_cluster.py --docker --init --nodes 3   # start a 3-node cluster
./pgraft_cluster.py --docker --status           # inspect status
./pgraft_cluster.py --docker --destroy          # tear down
```

See the [cluster script guide](https://pgelephant.github.io/pgraft/user-guide/pgraft-cluster-script/).

---

## Performance characteristics

| Metric | Typical value | Notes |
|---|---|---|
| Tick interval | 100 ms | Background-worker frequency |
| Election timeout | 1000 ms | Configurable (500 – 3000 ms recommended) |
| Heartbeat interval | 100 ms | Configurable (50 – 500 ms recommended) |
| Memory per node | ~50 MB | Go runtime and Raft state |
| CPU (idle) | < 1 % | Background-worker overhead |
| Failover time | 1 – 3 s | Election timeout plus detection |

---

## Production deployment

<details>
<summary>System requirements</summary>

| Resource | Minimum (testing) | Recommended (production) |
|---|---|---|
| CPU | 2 cores | 4+ cores |
| Memory | 2 GB / node | 8 GB+ / node |
| Disk | 10 GB | 50 GB+ SSD |
| Network | 100 Mbps | 1 Gbps+, < 10 ms latency |

</details>

Recommended practices:

- Run an **odd number of nodes** (3, 5, or 7) for a stable quorum.
- Keep inter-node latency **below 10 ms**.
- Use a **dedicated network** for Raft traffic where possible.
- **Monitor** leader changes and replication lag, and alert on them.
- Maintain regular **PostgreSQL backups** alongside Raft logs.
- **Test failover** thoroughly before going to production.

See the [best-practices guide](https://pgelephant.github.io/pgraft/operations/best-practices/).

---

## Troubleshooting

<details>
<summary>Background worker not starting</summary>

```sql
SHOW shared_preload_libraries;   -- must include 'pgraft'
```

`shared_preload_libraries` changes require a PostgreSQL restart.

</details>

<details>
<summary>No leader elected</summary>

```sql
SELECT pgraft_get_leader(), pgraft_is_leader();
```

Allow a few seconds after cluster start. Confirm that `pgraft.initial_cluster`
and `pgraft.initial_cluster_token` are identical on every node and that the peer
ports are reachable.

</details>

<details>
<summary>A node cannot join</summary>

```sql
SELECT name, setting FROM pg_settings WHERE name LIKE 'pgraft.%';
```

Verify that this node's `pgraft.name` appears in `pgraft.initial_cluster` and
that its `listen_peer_urls` endpoint is reachable from the other nodes.

</details>

<details>
<summary>High CPU usage</summary>

```sql
SELECT elections_triggered FROM pgraft_get_cluster_status();
```

Repeated elections usually indicate network instability or an
`election_timeout` that is too low for the link latency; increase it.

</details>

See the full [troubleshooting guide](https://pgelephant.github.io/pgraft/operations/troubleshooting/).

---

## Documentation

| Section | Topics |
|---|---|
| [Getting started](https://pgelephant.github.io/pgraft/getting-started/installation/) | Installation, quick start |
| [User guide](https://pgelephant.github.io/pgraft/user-guide/configuration/) | Configuration, SQL functions, cluster operations, tutorial |
| [Concepts](https://pgelephant.github.io/pgraft/concepts/architecture/) | Architecture, automatic replication, split-brain protection |
| [Operations](https://pgelephant.github.io/pgraft/operations/monitoring/) | Monitoring, troubleshooting, best practices |
| [Development](https://pgelephant.github.io/pgraft/development/building/) | Building, testing, contributing |

---

## Contributing

Contributions are welcome — bug reports, feature requests, documentation, and
code. A typical workflow:

1. Search existing [issues](https://github.com/pgelephant/pgraft/issues) and
   [discussions](https://github.com/pgelephant/pgraft/discussions).
2. Open an issue describing the problem or proposal.
3. Fork the repository and develop on a feature branch.
4. Submit a pull request with tests and documentation.

Please read the
[contributing guidelines](https://pgelephant.github.io/pgraft/development/contributing/)
before opening a pull request.

```bash
make installcheck   # regression tests
```

---

## Technology stack

| Component | Technology |
|---|---|
| Core language | C (PostgreSQL extension) |
| Consensus engine | Go — [etcd-io/raft](https://github.com/etcd-io/raft) |
| Build system | PostgreSQL PGXS, GNU Make |
| JSON parsing | json-c |
| Documentation | MkDocs (Material theme) |
| CI/CD | GitHub Actions |
| Packaging | RPM (RHEL/Rocky), DEB (Ubuntu/Debian) |

---

## License

---

Built for the PostgreSQL community.

[Documentation](https://pgelephant.github.io/pgraft/) ·
[Issues](https://github.com/pgelephant/pgraft/issues) ·
[Discussions](https://github.com/pgelephant/pgraft/discussions)

</div>

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