Redis: what's eating memory and time

Biggest keys

redis-cli --bigkeys

Walks the whole database with SCAN and shows the biggest key of each type.

Mind the units: for strings it counts bytes, for collections the number of elements. A list with a million short entries will look “bigger” here than a single 10 MB string.

What it actually weighs

redis-cli --memkeys

Same walk, but measured with MEMORY USAGE — real bytes. Slower, but it doesn’t lie. Redis 6 and up.

A single key:

redis-cli MEMORY USAGE mykey

Both walks cover the entire keyspace. On a large database add -i 0.1 so they pause between batches instead of hammering the server.

Command stats

INFO commandstats

How many times each command ran and how long it took on average (usec_per_call). Usually this is where it turns out Redis isn’t slow — somebody is just hammering KEYS in a loop.

Reset the counters before measuring:

CONFIG RESETSTAT