Consumers
Consumers receive messages from queues. A consumer is created by calling basic.consume on a channel, specifying the queue to consume from.
Consumer Lifecycle
basic.consume— registers a consumer on a queue, returns a consumer tag- Messages are pushed to the consumer as they become available
basic.cancel— unregisters the consumer
The consumer tag is a client-chosen string that identifies the consumer. If not provided, the server generates one.
Acknowledgment Modes
Auto-Ack (no_ack=true)
Messages are considered acknowledged as soon as they are delivered. No explicit ack is needed. Messages are removed from the queue immediately on delivery.
Use when message loss on consumer failure is acceptable.
Manual Ack (no_ack=false)
The consumer must explicitly acknowledge each message:
basic.ack— acknowledge (remove from queue)basic.reject— reject a single message (optionally requeue)basic.nack— reject one or more messages (optionally requeue). Supports themultipleflag to ack/nack all messages up to the delivery tag.
Unacknowledged messages are requeued if the consumer disconnects or the channel closes.
Prefetch (QoS)
Prefetch limits the number of unacknowledged messages the server will deliver to a consumer. Set via basic.qos:
| Parameter | Description |
|---|---|
prefetch_count |
Max unacknowledged messages |
global=false |
Per-consumer limit (default) |
global=true |
Per-channel limit, shared across all consumers on the channel |
Prefetch of 0 means unlimited delivery. The server-wide default applies when a consumer does not call basic.qos:
| Config Key | Section | Default | Description |
|---|---|---|---|
default_consumer_prefetch |
[main] |
65535 |
Default per-consumer prefetch |
Single Active Consumer
When a queue is declared with x-single-active-consumer: true, only one consumer receives messages at a time. If that consumer disconnects, the next registered consumer becomes active.
This is useful for ordered processing where only one consumer should handle messages from the queue.
Consumer Priority
Consumers can declare a priority via the x-priority argument on basic.consume. Higher-priority consumers receive messages before lower-priority ones. Default priority is 0.
When a high-priority consumer has reached its prefetch limit, messages are delivered to the next highest-priority consumer with available capacity.
Consumer Timeout
If the oldest unacknowledged message on a consumer has been waiting longer than the configured timeout, LavinMQ closes the channel. The timeout is measured from when the message was delivered, not from last channel activity, so acknowledging other messages does not reset the timer.
A per-queue override can be set with the x-consumer-timeout queue argument (milliseconds).
| Config Key | Section | Default | Description |
|---|---|---|---|
consumer_timeout |
[main] |
(none) | Server-wide consumer idle timeout (milliseconds) |
consumer_timeout_loop_interval |
[main] |
60 |
How often the timeout check runs (seconds) |
basic.get (Polling)
basic.get retrieves a single message from a queue synchronously. Unlike basic.consume, it does not register a persistent consumer. Each call fetches one message (or returns empty if the queue is empty).
basic.consume is preferred for throughput. basic.get is useful for batch processing or infrequent polling.
basic.recover
basic.recover asks the server to redeliver all unacknowledged messages on the channel.
requeue=true— messages are requeued and may be delivered to a different consumerrequeue=false— the server attempts to redeliver messages to the original consumer. If the consumer is no longer active, messages are requeued instead.
Exclusive Consumers
A consumer declared with exclusive: true ensures no other consumers can consume from the queue while it is active. If another consumer tries to consume from the same queue, a 403 ACCESS_REFUSED error is returned.
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