Managing Redis from the console · Redis Basics

Server info and monitoring

Watch a live Redis: read INFO memory and keyspace stats, stream commands with MONITOR, check SLOWLOG, and use --stat, --bigkeys, and --latency.

How to monitor a Redis server from the console

Deleting and inspecting keys tells you about data. To monitor a Redis server you ask different questions: how much memory it holds, what commands it is running right now, and which ones are slow. This lesson covers the four tools for that, INFO, MONITOR, SLOWLOG, and a set of redis-cli flags, the ones you reach for when something feels wrong.

INFO: the health snapshot

INFO dumps a big report about the server, grouped into sections:

127.0.0.1:6379> INFO
# Server
redis_version:7.2.4
# Memory
used_memory_human:1.51M
# Keyspace
db0:keys=42,expires=3,avg_ttl=0

The full output is long, so ask for one section at a time:

127.0.0.1:6379> INFO memory
127.0.0.1:6379> INFO keyspace
127.0.0.1:6379> INFO stats

The three you will use most:

  • memory: used_memory_human is how much RAM Redis holds right now. Watch this to catch leaks or runaway growth.
  • keyspace: how many keys each database holds, and how many have an expiry. A quick way to see if data is where you expect.
  • stats: totals like keyspace_hits and keyspace_misses (how often lookups found data), plus total_commands_processed.

One subtlety with those hit and miss numbers: they are running totals counted since the server last started, not a rate. A single reading tells you almost nothing. To judge whether your hit ratio is actually good, take two INFO stats samples a minute apart and compare the difference; that delta is the behaviour over that minute, which is what you care about.

MONITOR: watch commands live

MONITOR streams every command the server handles, as it happens:

127.0.0.1:6379> MONITOR
OK
1690000000.123 [0 127.0.0.1:51000] "GET" "user:42:name"
1690000000.456 [0 127.0.0.1:51000] "SET" "session:abc" "..."

It is fantastic for debugging: you see exactly what your application is asking Redis to do. Press Ctrl+C to stop.

The cost: MONITOR shows you everything, so on a busy server it produces a flood of output and adds real load (Redis has to copy every command to your stream). Use it for a few seconds to catch a problem, then quit. Never leave it running on production.

SLOWLOG: find slow commands

Redis records commands that took longer than a threshold in the slow log. Read the recent entries:

127.0.0.1:6379> SLOWLOG GET 10
1) 1) (integer) 0
   2) (integer) 1690000000
   3) (integer) 15000
   4) 1) "KEYS"
      2) "*"

10 asks for the last ten entries. Each entry shows an id, a timestamp, the duration in microseconds (15000 here is 15 ms), and the command itself. Notice the culprit above: someone ran KEYS *, exactly the mistake from the finding-keys lesson. SLOWLOG is how you catch it after the fact.

Useful redis-cli flags

These run from your shell, not the prompt, and each is a small monitoring tool on its own.

--stat prints a live one-line-per-second dashboard of key counts, memory, and requests:

redis-cli --stat

--bigkeys scans the database (safely, using SCAN) and reports the largest key of each type, perfect for finding what is eating your memory:

redis-cli --bigkeys

--latency measures how fast the server responds by pinging it continuously:

redis-cli --latency

It prints min, max, and average round-trip time in milliseconds. If those numbers climb, the server is under strain.

Common mistake

Leaving MONITOR running on a production server and walking away. It copies every single command to your connection, so on a busy instance it can noticeably slow Redis down and bury you in output. Treat it like a debugger you attach for a moment: turn it on, watch, then Ctrl+C. For ongoing health, use INFO and --stat instead, which are cheap.

FAQ

How do I check Redis memory usage?

Run INFO memory and read used_memory_human. To find which keys use the most, run redis-cli --bigkeys.

How do I see live Redis commands?

MONITOR streams every command as the server runs it. Use it briefly to debug, then stop with Ctrl+C, since it adds load and is not safe to leave on in production.

How do I find slow Redis commands?

SLOWLOG GET 10 shows the last ten commands that crossed the slow threshold, with their duration in microseconds and the exact command that was slow.

What does redis-cli --bigkeys do?

It scans the keyspace with SCAN (so it is safe) and reports the biggest key of each type. It is the fastest way to track down what is consuming your memory.