Metric to get oldest delay of any topic

[Mohamed-Irshad-git]

Hi all,
Is there any metric to get the timestamp or delay of the oldest message in a topic? I used pulsar v3.0 as a queue in my architecture so this is required to scale my consumers.

[yudin-s]

There is a metric for the age, but not usually a direct "oldest message timestamp" metric.

For Prometheus-style broker metrics, look for:

pulsar_storage_backlog_age_seconds

In the broker stats code this is populated from topic.getBestEffortOldestUnacknowledgedMessageAgeSeconds(), so it is the age in seconds of the oldest unacknowledged backlog message for the topic. That is usually the metric you want for "how old is the queue backlog?".

For autoscaling consumers, I would use it together with the subscription backlog count, for example:

pulsar_subscription_msg_backlog

Decision rule:

• pulsar_subscription_msg_backlog tells you how many messages are waiting for a subscription.
• pulsar_storage_backlog_age_seconds tells you how old the oldest unacknowledged backlog is.
• For partitioned topics, use max(...) across the topic partitions, because one hot/stuck partition is enough to require scaling or alerting.

Example PromQL shape:

max by (topic) (
  pulsar_storage_backlog_age_seconds{namespace="my-tenant/my-namespace"}
)

and combine that with:

sum by (topic, subscription) (
  pulsar_subscription_msg_backlog{namespace="my-tenant/my-namespace"}
)

One caveat: this is an age/delay value, not the original publish timestamp. If you need the exact timestamp, derive it in Prometheus as roughly time() - pulsar_storage_backlog_age_seconds, or query/admin-inspect topic/subscription state separately. For scaling, the age metric is normally better than a timestamp because it can be compared directly against an SLO threshold.

If that matches your queue-scaling use case, please mark this as answered so others looking for the backlog-age metric can find it.