The default that clears a TTL
No expiry and no KEEPTTL, so an existing expiry is discarded
- key
- session:abc
- value
- hello
- expiry
- ttl-seconds
Redis SET Command Builder
Build a SET with its options. The one that catches people: a SET without an expiry and without KEEPTTL removes whatever TTL the key already had, silently, so a cache entry becomes permanent.
set-command.txt
updates as you typeExamples
Worked setups you can load into the form above. Each one is a decision the generator makes differently, and the reason it makes it.
A lock
SET NX with an expiry, and why releasing it needs more than DEL
- key
- lock:orders
- value
- token-123
- mode
- only-if-new
- expiry
- seconds
- ttl-seconds
- 30
Common mistakes
These are the ones that fail silently. The config is accepted, nothing raises an error, and the consequence arrives later.
Rewriting a key with a plain SET and expecting the TTL to survive
It does not. The expiry is discarded and the key becomes permanent.
Instead:Pass KEEPTTL, or set the expiry again.
Releasing a SET NX lock with DEL
If your lock already expired, DEL removes whoever holds it now.
Instead:Use a Lua compare-and-delete against your token.
Using SETEX and a separate SETNX for a lock
Two commands are not atomic, so the process can die between them and leave a key with no expiry.
Instead:One SET with NX and EX together.
Assuming NX with GET works everywhere
It is a syntax error before Redis 7.0.
Instead:Check the server version, or use a script.
SET has more behaviour than it looks
It is the first command anybody learns and it has four options whose interaction decides whether data expires, whether a write is atomic, and whether it works at all on your server version.
A plain SET destroys the existing expiry
Rewriting a key with SET discards its TTL unless you pass KEEPTTL or set a new expiry. A key that was expiring in an hour becomes permanent. There is no error and no warning, and on a cache it means the key is never reclaimed until eviction pressure removes it.
SET NX with an expiry is a lock, and releasing it is the hard part
Acquiring is easy. The failure is releasing a lock that already expired and was taken by somebody else, because a plain DEL then deletes the other holder's lock. The release has to be a compare-and-delete that checks the value still matches your own token, which means a Lua script.
NX combined with GET needs Redis 7.0
Before 7.0 the server rejected that combination as a syntax error. It is genuinely useful, because it tells you the existing value in the same round trip in which your write was refused.
EXAT sets an absolute time, and needs 6.2
EX is relative to now, so recomputing a duration on every write lets the expiry drift forward indefinitely. EXAT takes a Unix timestamp and does not drift.
SETNX, SETEX and PSETEX are superseded
They still work and are not being removed. SET with options does everything they do and can combine an expiry with a conditional set in one atomic command, which they cannot.
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