Redis says the key is gone. The memory comes back 22 seconds later.

A key with a TTL stops existing the moment that TTL passes. GET returns nil, EXISTS returns 0, and as far as anything your application can observe, the key is gone. What I wanted to know was when the memory comes back, because those are not the same event and I had never seen anybody put a number on the gap. The answer, on an idle server with five million keys expiring together, is a little under twenty-three seconds. For most of that time Redis is holding several hundred megabytes for data that every client already agrees does not exist.