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TTL (Time-To-Live)

LavinMQ supports TTL for both messages and queues.

Message TTL

Message TTL controls how long a message can remain in a queue before it is discarded or dead-lettered.

Setting Message TTL

Message TTL can be set in two places:

  • Per-message — set the expiration property on the message (string value in milliseconds, e.g., "60000" for 60 seconds)
  • Per-queue — set the x-message-ttl queue argument or apply the message-ttl policy

When both per-message and per-queue TTL are set, the lower of the two applies. The effective deadline is calculated as (msg.timestamp + ttl) // 100 * 100 — that is, the publish time of the message plus the smaller TTL, truncated to the nearest 100 ms. Because the deadline is computed from msg.timestamp, changing the queue-level TTL retroactively affects messages already in the queue (they are re-evaluated against the new value at the next expiration check).

Zero TTL

A TTL of 0 means the message should be delivered immediately or expired. If at least one consumer is attached when the message arrives the message is delivered, otherwise it is expired (and dead-lettered if a DLX is configured) on the first expiration check.

Queue TTL (Expiration)

Queue TTL controls how long a queue can remain unused before it is automatically deleted.

Setting Queue TTL

  1. Per-queue — set the x-expires argument (integer in milliseconds, minimum 1)
  2. Via policy — set the expires policy key

Behavior

A per-queue background fiber (queue_expire_loop) sleeps until the queue's consumer count drops to zero, then starts a timer of x-expires milliseconds. The timer races against three signals:

  • a consumer attaches (the timer is reset by waiting for "no consumers" again),
  • x-expires is reconfigured (the new value is picked up on the next loop iteration), or
  • a basic.get is performed (the loop is poked and re-evaluates).

If none of those happen before the timer fires, the queue is closed and deleted along with all its messages. Note that "unused" only considers consumers — publishing to the queue does not by itself reset the expiration timer.

Interaction with Dead-Lettering

Expired messages (both from message TTL and queue overflow) can be dead-lettered if a dead letter exchange is configured. The dead-letter reason is expired. See Dead Lettering.