[](https://crates.io/crates/pg_walstream)
[](https://crates.io/crates/pg_walstream)
[](https://crates.io/crates/pg_walstream)
[](https://docs.rs/pg-walstream)
[](https://codecov.io/gh/isdaniel/pg-walstream)
# pg-walstream
A high-performance Rust library for PostgreSQL logical and physical replication protocol parsing and streaming. This library provides a robust, type-safe interface for consuming PostgreSQL Write-Ahead Log (WAL) streams.
## Features
- **Full Logical Replication Support**: Implements PostgreSQL logical replication protocol versions 1-4
- **Physical Replication Support**: Stream raw WAL data for standby servers and PITR
- **Streaming Transactions**: Support for streaming large transactions (protocol v2+)
- **Two-Phase Commit**: Prepared transaction support (protocol v3+)
- **Parallel Streaming**: Multi-stream parallel replication (protocol v4+)
- **Zero-Copy Operations**: Efficient buffer management using the `bytes` crate
- **Thread-Safe LSN Tracking**: Atomic LSN feedback for producer-consumer patterns
- **Connection Management**: Built-in connection handling with exponential backoff retry logic
- **Type-Safe API**: Strongly typed message parsing with comprehensive error handling
- **Configurable Slot Options**: Temporary slots, snapshot export, two-phase, and failover support
## Installation
Add this to your `Cargo.toml`:
```toml
[dependencies]
pg_walstream = "0.1.0"
```
## System Dependencies
Make sure you have libpq development libraries installed:
**Ubuntu/Debian:**
```bash
sudo apt-get install libpq-dev \
clang \
libclang-dev
```
**CentOS/RHEL/Fedora:**
```bash
sudo yum install postgresql-devel
# or
sudo dnf install postgresql-devel
```
## Quick Start
### Logical Replication - Stream API
The Stream API provides an ergonomic, iterator-like interface:
```rust
use pg_walstream::{
LogicalReplicationStream, ReplicationStreamConfig, ReplicationSlotOptions,
RetryConfig, StreamingMode, SharedLsnFeedback, CancellationToken,
};
use std::sync::Arc;
use std::time::Duration;
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
// Configure the replication stream
let config = ReplicationStreamConfig::new(
"my_slot".to_string(), // Replication slot name
"my_publication".to_string(), // Publication name
2, // Protocol version
StreamingMode::On, // Streaming mode
Duration::from_secs(10), // Feedback interval
Duration::from_secs(30), // Connection timeout
Duration::from_secs(60), // Health check interval
RetryConfig::default(), // Retry configuration
)
// Optional: configure slot creation options
.with_slot_options(ReplicationSlotOptions {
temporary: true,
snapshot: Some("export".to_string()),
..Default::default()
});
// Create and initialize the stream
let mut stream = LogicalReplicationStream::new(
"postgresql://postgres:password@localhost:5432/mydb?replication=database",
config,
).await?;
stream.start(None).await?;
// If the slot was created with EXPORT_SNAPSHOT, use the snapshot name on a SEPARATE regular connection to read the initial table state:
// BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ;
// SET TRANSACTION SNAPSHOT '<snapshot_name>';
// COPY my_table TO STDOUT; -- or SELECT * FROM my_table
// COMMIT;
if let Some(snapshot_name) = stream.exported_snapshot_name() {
println!("Exported snapshot: {}", snapshot_name);
}
// Create cancellation token for graceful shutdown
let cancel_token = CancellationToken::new();
// Convert to async Stream - provides iterator-like interface
let mut event_stream = stream.into_stream(cancel_token);
// Process events using Stream combinators
loop {
match event_stream.next().await {
Ok(event) => {
println!("Received event: {:?}", event);
// Update LSN feedback using the convenient method
event_stream.update_applied_lsn(event.lsn.value());
}
Err(e) if matches!(e, pg_walstream::ReplicationError::Cancelled(_)) => {
println!("Stream cancelled, shutting down gracefully");
break;
}
Err(e) => {
eprintln!("Error: {}", e);
break;
}
}
}
Ok(())
}
```
> **Note:** The exported snapshot is only valid while the transaction that created the
> replication slot is still open. You must read the snapshot **before** consuming WAL events
> or closing the replication connection. Temporary slots are automatically recreated on
> connection recovery.
### Working with Event Data
Events carry row data as `RowData` — an ordered list of `(Arc<str>, Value)` pairs.
Schema, table, and column names are `Arc<str>` (reference-counted, zero-cost cloning):
```rust
use pg_walstream::{EventType, RowData};
// Pattern match on event types
match &event.event_type {
EventType::Insert { schema, table, data, .. } => {
// schema and table are Arc<str> — Display works directly
println!("INSERT into {}.{}", schema, table);
// Access columns by name
if let Some(id) = data.get("id") {
println!(" id = {}", id);
}
// Iterate over all columns
for (col_name, value) in data.iter() {
println!(" {} = {}", col_name, value);
}
}
EventType::Update { old_data, new_data, key_columns, .. } => {
// key_columns is Vec<Arc<str>>
println!("Key columns: {:?}", key_columns);
println!("New data has {} columns", new_data.len());
}
EventType::Delete { old_data, .. } => {
// Convert to HashMap if needed for downstream compatibility
let map = old_data.clone().into_hash_map();
println!("Deleted row: {:?}", map);
}
_ => {}
}
```
### Using the Polling API
For more control, you can use the traditional polling approach:
```rust
use pg_walstream::{
LogicalReplicationStream, ReplicationStreamConfig, RetryConfig, StreamingMode,
SharedLsnFeedback, CancellationToken,
};
use std::sync::Arc;
use std::time::Duration;
#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
let config = ReplicationStreamConfig::new(
"my_slot".to_string(),
"my_publication".to_string(),
2, StreamingMode::On,
Duration::from_secs(10),
Duration::from_secs(30),
Duration::from_secs(60),
RetryConfig::default(),
);
let mut stream = LogicalReplicationStream::new(
"postgresql://postgres:password@localhost:5432/mydb?replication=database",
config,
).await?;
stream.start(None).await?;
let cancel_token = CancellationToken::new();
// Traditional polling loop with automatic retry
loop {
match stream.next_event_with_retry(&cancel_token).await {
Ok(event) => {
println!("Received event: {:?}", event);
stream.shared_lsn_feedback.update_applied_lsn(event.lsn.value());
}
Err(e) if matches!(e, pg_walstream::ReplicationError::Cancelled(_)) => {
println!("Cancelled, shutting down gracefully");
break;
}
Err(e) => {
eprintln!("Error: {}", e);
break;
}
}
}
Ok(())
}
```
## LSN Tracking
Thread-safe LSN tracking for feedback to PostgreSQL:
```rust
use pg_walstream::SharedLsnFeedback;
use std::sync::Arc;
let feedback = SharedLsnFeedback::new_shared();
// Producer thread: read LSN from feedback
let (flushed_lsn, applied_lsn) = feedback.get_feedback_lsn();
// Consumer thread: update LSN after processing
feedback.update_applied_lsn(commit_lsn);
```
## PostgreSQL Setup
Before using this library, you need to configure PostgreSQL for replication:
### 1. Configure PostgreSQL
Edit `postgresql.conf`:
```conf
wal_level = logical
max_replication_slots = 4
max_wal_senders = 4
```
Restart PostgreSQL after making these changes.
### 2. Create a Publication
```sql
-- Create a publication for specific tables
CREATE PUBLICATION my_publication FOR TABLE users, orders;
-- Or publish all tables
CREATE PUBLICATION my_publication FOR ALL TABLES;
```
### 3. Create Replication User
```sql
-- Create a user with replication privileges
CREATE USER replication_user WITH REPLICATION PASSWORD 'secure_password';
-- Grant necessary permissions
GRANT SELECT ON ALL TABLES IN SCHEMA public TO replication_user;
GRANT USAGE ON SCHEMA public TO replication_user;
```
### 4. Create Replication Slot with Advanced Options
The library provides two methods for creating replication slots:
#### Replication Slot Options
The library automatically selects the correct `CREATE_REPLICATION_SLOT` SQL syntax based on the connected PostgreSQL server version:
- **PG14**: Legacy positional keyword syntax (`EXPORT_SNAPSHOT`, `NOEXPORT_SNAPSHOT`, `USE_SNAPSHOT`, `TWO_PHASE`, `RESERVE_WAL`)
- **PG15+**: Modern parenthesized options syntax (`(SNAPSHOT 'export', TWO_PHASE true, ...)`)
| `temporary` | Temporary slot (not persisted to disk, dropped on disconnect) | 14+ |
| `two_phase` | Enable two-phase commit for logical slots | 14+ |
| `reserve_wal` | Reserve WAL immediately for physical slots | 14+ |
| `snapshot` | Snapshot behavior: `"export"`, `"use"`, or `"nothing"` | 14+ |
| `failover` | Enable slot synchronization to standbys for HA | 16+ |
> **Note:** : If both `two_phase` and `snapshot` are set, `two_phase` takes priority. The `failover` option is not available on PG14 and will return an error.
## Message Types
The library supports all PostgreSQL logical replication message types:
### Protocol Version 1 Messages
- **BEGIN**: Transaction start
- **COMMIT**: Transaction commit
- **ORIGIN**: Replication origin
- **RELATION**: Table schema definition
- **TYPE**: Data type definition
- **INSERT**: Row insertion
- **UPDATE**: Row update
- **DELETE**: Row deletion
- **TRUNCATE**: Table truncation
- **MESSAGE**: Generic message
### Protocol Version 2+ Messages (Streaming)
- **STREAM_START**: Streaming transaction start
- **STREAM_STOP**: Streaming transaction segment end
- **STREAM_COMMIT**: Streaming transaction commit
- **STREAM_ABORT**: Streaming transaction abort
### Protocol Version 3+ Messages (Two-Phase Commit)
- **BEGIN_PREPARE**: Prepared transaction start
- **PREPARE**: Transaction prepare
- **COMMIT_PREPARED**: Commit prepared transaction
- **ROLLBACK_PREPARED**: Rollback prepared transaction
- **STREAM_PREPARE**: Stream prepare message
## Architecture
```
┌─────────────────────────────────────────┐
│ Application Layer │
│ (Your CDC / Replication Logic) │
└──────────────┬──────────────────────────┘
│
┌──────────────▼──────────────────────────┐
│ LogicalReplicationStream │
│ - Connection management │
│ - Event processing │
│ - LSN feedback │
└──────────────┬──────────────────────────┘
│
┌──────────────▼──────────────────────────┐
│ LogicalReplicationParser │
│ - Protocol parsing │
│ - Message deserialization │
└──────────────┬──────────────────────────┘
│
┌──────────────▼──────────────────────────┐
│ BufferReader / BufferWriter │
│ - Zero-copy operations │
│ - Binary protocol handling │
└─────────────────────────────────────────┘
```
## Performance Considerations
- **Zero-Copy**: Uses `bytes::Bytes` for efficient buffer management
- **Arc-shared column metadata**: Column names, schema, and table names use `Arc<str>` — cloning is a single atomic increment instead of a heap allocation per event
- **RowData (ordered Vec)**: Row payloads use `RowData` (a `Vec<(Arc<str>, Value)>`) instead of `HashMap<String, Value>`, eliminating per-event hashing overhead and extra allocations
- **Atomic Operations**: Thread-safe LSN tracking with minimal overhead
- **Connection Pooling**: Reusable connection with automatic retry
- **Streaming Support**: Handle large transactions without memory issues
- **Efficient Blocking**: Async I/O with tokio::select eliminates busy-waiting
## Limitations
- Requires PostgreSQL 14 or later for full protocol support
- Logical replication slot must be created before streaming
- Binary protocol only (no text-based protocol support)
- Requires `replication` permission for the database user
## Resources
- [PostgreSQL Logical Replication Documentation](https://www.postgresql.org/docs/current/logical-replication.html)
- [Logical Replication Message Formats](https://www.postgresql.org/docs/current/protocol-logicalrep-message-formats.html)
- [Replication Protocol](https://www.postgresql.org/docs/current/protocol-replication.html)
## Contributing
Contributions are welcome! Please feel free to submit a Pull Request.
## Author
Daniel Shih (dog830228@gmail.com)