PostgreSQL Message Broker

Reference · Applies to Brighter V10

Brighter supports for using PostgreSQL as a message broker, enabling pub/sub messaging patterns using your existing PostgreSQL infrastructure.

PostgreSQL Message Broker Overview

The PostgreSQL message broker uses a table-based queue approach where messages are stored in a PostgreSQL table and retrieved by consumers. This provides a lightweight messaging solution that leverages your existing PostgreSQL database without requiring additional message broker infrastructure.

How the PostgreSQL Broker Works

1. Producer: Inserts messages into a queue store table

2. Consumer: Retrieves messages from the queue store table based on visibility timeout

3. Acknowledgement: Deletes processed messages from the table

4. Reject/Requeue: Deletes or updates messages based on processing outcome

The system uses a visibility timeout mechanism (similar to AWS SQS) where messages become invisible to other consumers once retrieved, preventing duplicate processing.

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PostgreSQL Message Broker Configuration

NuGet Package

Install the PostgreSQL messaging gateway package:

dotnet add package Paramore.Brighter.MessagingGateway.Postgres

Database Table

Create the queue store table in your PostgreSQL database:

CREATE TABLE IF NOT EXISTS {schema}.{queue_store_table}
(
    "id" BIGSERIAL PRIMARY KEY,
    "queue" VARCHAR(255) NOT NULL,
    "content" JSONB NOT NULL,
    "visible_timeout" TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    "created_at" TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
);

CREATE INDEX IF NOT EXISTS idx_{queue_store_table}_queue_visible
    ON {schema}.{queue_store_table}("queue", "visible_timeout");

Index Requirements: The index on (queue, visible_timeout) is critical for performance.

---

Producer Configuration

Basic Producer Setup

using Paramore.Brighter;
using Paramore.Brighter.MessagingGateway.Postgres;
using Paramore.Brighter.PostgreSql;

// Database configuration
var postgresConfiguration = new RelationalDatabaseConfiguration(
    connectionString: "Host=localhost;Database=myapp;Username=user;Password=pass",
    queueStoreTable: "brighter_messages",
    schemaName: "public",
    binaryMessagePayload: true  // Use JSONB for better performance
);

// Publication configuration
var publications = new List<PostgresPublication>
{
    new PostgresPublication<OrderCreatedEvent>
    {
        Topic = new RoutingKey("orders.created"),
        SchemaName = "public",
        QueueStoreTable = "brighter_messages",
        BinaryMessagePayload = true  // JSONB
    }
};

// Producer registry
var producerRegistry = new PostgresProducerRegistryFactory(
    postgresConfiguration,
    publications
).Create();

// Configure Brighter
services.AddBrighter(options =>
{
    options.HandlerLifetime = ServiceLifetime.Scoped;
})
.AddProducers(configure =>
{
    configure.ProducerRegistry = producerRegistry;
})
.AutoFromAssemblies();

Publishing Messages

public class OrderService
{
    private readonly IAmACommandProcessor _commandProcessor;

    public OrderService(IAmACommandProcessor commandProcessor)
    {
        _commandProcessor = commandProcessor;
    }

    public async Task CreateOrderAsync(CreateOrderCommand command)
    {
        // Process order
        var order = ProcessOrder(command);

        // Publish event
        var orderCreatedEvent = new OrderCreatedEvent
        {
            OrderId = order.Id,
            CustomerId = order.CustomerId,
            TotalAmount = order.TotalAmount,
            CreatedAt = DateTime.UtcNow
        };

        await _commandProcessor.PublishAsync(orderCreatedEvent);
    }
}

---

Consumer Configuration

Basic Consumer Setup

using Paramore.Brighter;
using Paramore.Brighter.MessagingGateway.Postgres;
using Paramore.Brighter.PostgreSql;

// Database configuration
var postgresConfiguration = new RelationalDatabaseConfiguration(
    connectionString: "Host=localhost;Database=myapp;Username=user;Password=pass",
    queueStoreTable: "brighter_messages",
    schemaName: "public",
    binaryMessagePayload: true
);

// Subscription configuration
var subscriptions = new List<PostgresSubscription>
{
    new PostgresSubscription<OrderCreatedEvent>(
        channelName: new ChannelName("orders.created.consumer"),
        routingKey: new RoutingKey("orders.created"),
        bufferSize: 10,                         // Number of messages to retrieve at once
        noOfPerformers: 1,                      // Number of concurrent consumers
        timeOut: TimeSpan.FromSeconds(30),
        messagePumpType: MessagePumpType.Proactor,
        makeChannels: OnMissingChannel.Create,
        visibleTimeout: TimeSpan.FromSeconds(30), // Message visibility timeout
        schemaName: "public",
        queueStoreTable: "brighter_messages",
        binaryMessagePayload: true
    )
};

// Channel factory
var channelFactory = new PostgresChannelFactory(postgresConfiguration);

// Configure Brighter Consumer
services.AddConsumers(options =>
{
    options.Subscriptions = subscriptions;
    options.DefaultChannelFactory = channelFactory;
})
.AutoFromAssemblies();

Consuming Messages

public class OrderCreatedEventHandler : RequestHandlerAsync<OrderCreatedEvent>
{
    private readonly IEmailService _emailService;
    private readonly ILogger<OrderCreatedEventHandler> _logger;

    public OrderCreatedEventHandler(
        IEmailService emailService,
        ILogger<OrderCreatedEventHandler> logger)
    {
        _emailService = emailService;
        _logger = logger;
    }

    public override async Task<OrderCreatedEvent> HandleAsync(
        OrderCreatedEvent @event,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Processing order created event for Order {OrderId}",
            @event.OrderId);

        // Send confirmation email
        await _emailService.SendOrderConfirmationAsync(@event);

        return await base.HandleAsync(@event, cancellationToken);
    }
}

---

PostgreSQL Message Broker Configuration Options

Three of the four settings below default to null, and a null is not "unset": the schema, the queue store table and the payload format each fall back to the same setting on the relational database configuration the connection carries, and the schema falls back once more to public.

PostgresPublication Options

PostgresPublication takes its options as properties and adds these three to the base publication options, which carry Topic.

Option	Type	Default	Description
SchemaName	string?	null	The schema the queue store table lives in.
QueueStoreTable	string?	null	The table messages are written to.
BinaryMessagePayload	bool?	null	Whether the payload column is written as JSONB rather than JSON.

PostgresSubscription Options

PostgresSubscription takes its options as constructor arguments, so the option is the parameter you type. The seventeen it shares with Subscription behave the same way here; the other seven are PostgreSQL's own.

Option	Type	Default	Description
subscriptionName	SubscriptionName	none	Names the subscription for diagnostics; read back as Name.
channelName	ChannelName	none	Names the queue this subscription reads.
routingKey	RoutingKey	none	The routing key messages are written under.
dataType	Type?	none	The request type messages on this queue are translated into; read back as RequestType.
getRequestType	Func<Message, Type>?	derives the type from dataType	Determines the request type from the message rather than from the queue.
bufferSize	int	1	Messages read from the queue at once and held in the channel.
noOfPerformers	int	1	Threads reading this queue, each with its own message pump.
timeOut	TimeSpan?	300 ms	How long a read waits before treating the queue as empty.
requeueCount	int	-1	Times a message is requeued before it is treated as a poison pill; -1 is unlimited.
requeueDelay	TimeSpan?	0 ms	How long delivery of a requeued message is delayed.
unacceptableMessageLimit	int	0	Unacceptable messages before the channel stops; 0 disables the limit.
unacceptableMessageLimitWindow	TimeSpan?	null	The window the unacceptable-message count resets at the end of.
messagePumpType	MessagePumpType	none	Selects the Reactor or Proactor concurrency model.
channelFactory	IAmAChannelFactory?	null	Creates the channel; falls back to DefaultChannelFactory when null.
makeChannels	OnMissingChannel	Create	Whether Brighter creates the queue store table, validates it, or assumes it.
emptyChannelDelay	TimeSpan?	500 ms	How long the pump pauses after a read that found no message.
channelFailureDelay	TimeSpan?	1000 ms	How long the pump pauses after a channel failure.
schemaName	string?	null	The schema the queue store table lives in.
queueStoreTable	string?	null	The table messages are read from.
visibleTimeout	TimeSpan?	30000 ms	How long a read message stays invisible to other consumers.
tableWithLargeMessage	bool	false	Whether payloads are read as streams to support large messages.
binaryMessagePayload	bool?	null	Whether the payload column is read as JSONB rather than JSON.
deadLetterRoutingKey	RoutingKey?	null	The routing key messages are dead-lettered to.
invalidMessageRoutingKey	RoutingKey?	null	The routing key unacceptable messages are routed to.

The request type parameter is dataType here rather than requestType, which is what every other transport in this documentation calls it, and it is read back as RequestType.

The generic form PostgresSubscription<T>, which every example above uses, takes the same options and supplies four defaults the table cannot: dataType is T, and subscriptionName, channelName and routingKey are T's full name. It leaves messagePumpType required, so state Reactor or Proactor on every subscription.

PostgresMessagingGatewayConnection Options

The connection wraps the relational database configuration rather than adding settings of its own.

Option	Type	Default	Description
configuration	RelationalDatabaseConfiguration	none	The connection string, schema and table names for the queue store; read back as Configuration.

The eight options on that configuration are documented once, at Relational Database Configuration Reference, because seventeen Brighter components share them.

---

Message Visibility

The PostgreSQL message broker uses a visibility timeout mechanism to prevent duplicate processing:

How Message Visibility Works

1. Message Published: visible_timeout set to CURRENT_TIMESTAMP

2. Message Retrieved: Consumer reads messages where visible_timeout <= CURRENT_TIMESTAMP

3. Processing: Message becomes invisible to other consumers (timeout not updated)

4. Acknowledged: Message deleted from table

5. Timeout Expires: If not acknowledged, message becomes visible again

Visibility Timeout Example

var subscription = new PostgresSubscription<OrderEvent>(
    // Message invisible for 60 seconds after retrieval
    visibleTimeout: TimeSpan.FromSeconds(60)
);

Recommendation: Set visibility timeout to 2-3x your expected processing time to account for retries and delays.

---

Scheduled Messages

PostgreSQL message broker supports message scheduling using the visibility timeout:

// ...
// Schedule message for future delivery
var delayedEvent = new OrderReminderEvent
{
    OrderId = orderId,
    ReminderText = "Your order ships tomorrow!"
};

await _commandProcessor.PublishAsync(
    TimeSpan.FromHours(24),        // Deliver in 24 hours
    delayedEvent
);

How it works: The visible_timeout is set to CURRENT_TIMESTAMP + delay, making the message invisible until the scheduled time.

---

Transactional Messaging

A key advantage of PostgreSQL as a message broker is transactional messaging with your business data:

Using the Outbox Pattern

public class OrderService
{
    private readonly OrderDbContext _dbContext;
    private readonly IAmACommandProcessor _commandProcessor;

    public async Task CreateOrderAsync(CreateOrderCommand command)
    {
        using var transaction = await _dbContext.Database.BeginTransactionAsync();

        try
        {
            // 1. Save order to database
            var order = new Order { /* ... */ };
            _dbContext.Orders.Add(order);
            await _dbContext.SaveChangesAsync();

            // 2. Deposit event to Outbox (same transaction)
            var orderCreatedEvent = new OrderCreatedEvent { /* ... */ };
            await _commandProcessor.DepositPostAsync(orderCreatedEvent);

            // 3. Commit transaction (atomically saves order and outbox message)
            await transaction.CommitAsync();

            // 4. Clear outbox to publish message
            await _commandProcessor.ClearOutboxAsync(new[] { orderCreatedEvent.Id });
        }
        catch
        {
            await transaction.RollbackAsync();
            throw;
        }
    }
}

See Outbox Pattern and PostgreSQL Outbox for more details.

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PostgreSQL Message Broker Monitoring and Observability

Query Queue Depth

-- Current queue depth by queue
SELECT
    "queue",
    COUNT(*) as message_count,
    MIN("visible_timeout") as oldest_visible,
    MAX("created_at") as newest_message
FROM "public"."brighter_messages"
WHERE "visible_timeout" <= CURRENT_TIMESTAMP
GROUP BY "queue"
ORDER BY message_count DESC;

Query In-Flight Messages

-- Messages currently being processed (invisible)
SELECT
    "queue",
    COUNT(*) as in_flight_count
FROM "public"."brighter_messages"
WHERE "visible_timeout" > CURRENT_TIMESTAMP
GROUP BY "queue";

Find Stuck Messages

-- Messages invisible for too long (potential failures)
SELECT
    "id",
    "queue",
    "created_at",
    "visible_timeout",
    EXTRACT(EPOCH FROM (CURRENT_TIMESTAMP - "visible_timeout")) as seconds_overdue
FROM "public"."brighter_messages"
WHERE "visible_timeout" < CURRENT_TIMESTAMP - INTERVAL '5 minutes'
ORDER BY "created_at";

OpenTelemetry Integration

PostgreSQL message broker operations are automatically traced when OpenTelemetry is configured:

services.AddOpenTelemetry()
    .WithTracing(tracing =>
    {
        tracing
            .AddSource("paramore.brighter")
            .AddNpgsql()  // PostgreSQL spans
            .AddOtlpExporter();
    });

---

PostgreSQL Message Broker Best Practices

1. Use JSONB for Production

var configuration = new RelationalDatabaseConfiguration(
    connectionString: connectionString,
    binaryMessagePayload: true  // JSONB for better performance
);

2. Set Appropriate Visibility Timeout

var subscription = new PostgresSubscription<OrderEvent>(
    // 2-3x expected processing time
    visibleTimeout: TimeSpan.FromMinutes(5)  // Handler takes ~2 minutes max
);

3. Use Connection Pooling

// Connection string with pooling
var connectionString = "Host=localhost;Database=myapp;Username=user;Password=pass;" +
                      "Minimum Pool Size=5;Maximum Pool Size=20";  // Connection pool

4. Monitor Queue Depth

Set up alerts for queue depth:

-- Alert if queue depth > 1000
SELECT COUNT(*) FROM brighter_messages WHERE queue = 'orders.created';

5. Index Your Queue Table

-- Critical index for performance
CREATE INDEX IF NOT EXISTS idx_messages_queue_visible
    ON brighter_messages("queue", "visible_timeout");

6. Regular Cleanup

Implement cleanup for old messages (if not using auto-vacuum):

-- Delete messages older than 7 days
DELETE FROM brighter_messages
WHERE "created_at" < CURRENT_TIMESTAMP - INTERVAL '7 days';

7. Use Claim Check for Large Messages

For messages > 100KB, use the Claim Check pattern:

[ClaimCheck(threshold: 102400, dataStore: typeof(S3LuggageStore))]
public class ProcessLargeOrderCommand : Command
{
    public byte[] LargePayload { get; set; }  // Stored in S3, not in database
}

8. Separate Queue Tables for High Volume

For high-volume queues, use dedicated tables:

// High-volume queue
var highVolumeSubscription = new PostgresSubscription<HighVolumeEvent>(
    queueStoreTable: "brighter_high_volume_messages"  // Separate table
);

// Normal queue
var normalSubscription = new PostgresSubscription<NormalEvent>(
    queueStoreTable: "brighter_messages"  // Shared table
);

---

PostgreSQL Message Broker Troubleshooting

Messages Not Being Consumed

Problem: Messages remain in the queue but are not processed.

Solutions:

1. Check visibility timeout hasn't expired:

   SELECT * FROM brighter_messages
   WHERE queue = 'your.queue' AND visible_timeout > CURRENT_TIMESTAMP;

2. Verify consumer is running and subscriptions match queue names

3. Check database connection pooling isn't exhausted

4. Review logs for consumer exceptions

High Database Load

Problem: PostgreSQL CPU/disk usage is high.

Solutions:

1. Verify index exists on (queue, visible_timeout)

2. Use JSONB instead of JSON for better performance

3. Reduce BufferSize if retrieving too many messages at once

4. Consider partitioning the queue table for high volume

5. Use connection pooling to reduce connection overhead

Messages Processed Multiple Times

Problem: Same message processed by multiple consumers.

Solutions:

1. Increase visibleTimeout to allow more processing time

2. Implement Inbox pattern for idempotency

3. Check for long-running handlers that exceed visibility timeout

4. Verify only one consumer process per subscription

Slow Message Retrieval

Problem: Consumer polls are slow.

Solutions:

1. Add index: CREATE INDEX ON brighter_messages(queue, visible_timeout)

2. Use JSONB instead of JSON

3. Increase timeOut to reduce polling frequency

4. Consider using bufferSize > 1 to retrieve multiple messages per poll

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Further Reading

• PostgreSQL Broker Trade-Offs - Benefits, limits, JSON vs JSONB, and how it compares

• PostgreSQL Outbox

• PostgreSQL Inbox

• Outbox Pattern

• Claim Check Pattern

• OpenTelemetry Integration

• Transactional Messaging

• PostgreSQL Documentation

• Npgsql - .NET PostgreSQL Driver