SET
SET key value [NX | XX] [GET] [EX seconds | PX milliseconds | EXAT unix-time-seconds | PXAT unix-time-milliseconds | KEEPTTL]
- Available since:
- 1.0.0
- Time complexity:
- O(1)
- ACL categories:
-
@write
,@string
,@slow
,
Set key
to hold the string value
.
If key
already holds a value, it is overwritten, regardless of its type.
Any previous time to live associated with the key is discarded on successful SET
operation.
Options
The SET
command supports a set of options that modify its behavior:
EX
seconds -- Set the specified expire time, in seconds.PX
milliseconds -- Set the specified expire time, in milliseconds.EXAT
timestamp-seconds -- Set the specified Unix time at which the key will expire, in seconds.PXAT
timestamp-milliseconds -- Set the specified Unix time at which the key will expire, in milliseconds.NX
-- Only set the key if it does not already exist.XX
-- Only set the key if it already exists.KEEPTTL
-- Retain the time to live associated with the key.GET
-- Return the old string stored at key, or nil if key did not exist. An error is returned andSET
aborted if the value stored at key is not a string.
Note: Since the SET
command options can replace SETNX
, SETEX
, PSETEX
, GETSET
, it is possible that in future versions of Redis these commands will be deprecated and finally removed.
Examples
Code examples
Patterns
Note: The following pattern is discouraged in favor of the Redlock algorithm which is only a bit more complex to implement, but offers better guarantees and is fault tolerant.
The command SET resource-name anystring NX EX max-lock-time
is a simple way to implement a locking system with Redis.
A client can acquire the lock if the above command returns OK
(or retry after some time if the command returns Nil), and remove the lock just using DEL
.
The lock will be auto-released after the expire time is reached.
It is possible to make this system more robust modifying the unlock schema as follows:
- Instead of setting a fixed string, set a non-guessable large random string, called token.
- Instead of releasing the lock with
DEL
, send a script that only removes the key if the value matches.
This avoids that a client will try to release the lock after the expire time deleting the key created by another client that acquired the lock later.
An example of unlock script would be similar to the following:
if redis.call("get",KEYS[1]) == ARGV[1]
then
return redis.call("del",KEYS[1])
else
return 0
end
The script should be called with EVAL ...script... 1 resource-name token-value
RESP2 Reply
Any of the following:
- Nil reply:
GET
not given: Operation was aborted (conflict with one of theXX
/NX
options). - Simple string reply:
OK
.GET
not given: The key was set. - Nil reply:
GET
given: The key didn't exist before theSET
. - Bulk string reply:
GET
given: The previous value of the key.
RESP3 Reply
Any of the following:
- Null reply:
GET
not given: Operation was aborted (conflict with one of theXX
/NX
options). - Simple string reply:
OK
.GET
not given: The key was set. - Null reply:
GET
given: The key didn't exist before theSET
. - Bulk string reply:
GET
given: The previous value of the key.
History
- Starting with Redis version 2.6.12: Added the
EX
,PX
,NX
andXX
options. - Starting with Redis version 6.0.0: Added the
KEEPTTL
option. - Starting with Redis version 6.2.0: Added the
GET
,EXAT
andPXAT
option. - Starting with Redis version 7.0.0: Allowed the
NX
andGET
options to be used together.