# Monitoring Streams and Consumer Groups — Redis Pub/Sub & Streams

Source: https://www.skillbyai.com/en/redis-streams/o-monitor

> Measure lag, pending entries and memory with XINFO and metrics.

## Is anyone falling behind?

For each stream, watch its **length**, **memory** and **growth rate**. For each consumer group, watch **lag** and **pending entries**. `XINFO STREAM` shows length, first and last entries and the number of groups. `XINFO GROUPS` lists groups with their consumers, **pending** count, **last-delivered-id**, and, since Redis 7, **entries-read** and **lag** (entries not yet delivered to the group, when Redis can compute it). `XINFO CONSUMERS` shows each consumer's pending count and **idle** time, which reveals dead consumers. `XPENDING` summarises unacknowledged entries. Export these to your monitoring system (for example, Prometheus via `redis_exporter`, which can be configured to collect stream metrics) and alert on growing lag, a PEL that keeps growing, consumers idle with pending entries, and memory approaching `maxmemory`. For Pub/Sub, watch the number of subscribers per channel and client output buffer sizes.

## Inspecting groups and consumers

Lag and pending counts tell you whether consumers keep up.

```bash
XINFO STREAM events:orders
# length, radix-tree keys/nodes, last-generated-id, groups, first-entry, last-entry

XINFO GROUPS events:orders
# name, consumers, pending, last-delivered-id, entries-read, lag

XINFO CONSUMERS events:orders billing
# name, pending, idle (ms since last interaction), inactive

XPENDING events:orders billing
XPENDING events:orders billing IDLE 60000 - + 10    # entries idle over 60 s
```

## Queue length at a ticket counter

Lag is the number of people waiting to be served; pending is the number currently at the counter. If the queue grows all morning, you need another counter (consumer); if one counter has had the same person for an hour, the clerk has gone missing.

**Quiz:** Which XINFO GROUPS field (Redis 7+) shows how many entries a group has not yet received?

- [ ] idle
- [ ] radix-tree-nodes
- [ ] last-generated-id
- [x] lag

*Answer:* lag. The lag field reports entries added to the stream that the group has not yet read.