SET key value [NX | XX] [GET] [EX | PX | EXAT | PXAT | KEEPTTL]
Available since
Time complexity
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 (a positive integer).
  • PX milliseconds – Set the specified expire time, in milliseconds (a positive integer).
  • EXAT timestamp-seconds – Set the specified Unix time at which the key will expire, in seconds (a positive integer).
  • PXAT timestamp-milliseconds – Set the specified Unix time at which the key will expire, in milliseconds (a positive integer).
  • 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 and SET 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 Redict these commands will be deprecated and finally removed.

Examples #

SET mykey "Hello"
GET mykey

SET anotherkey "will expire in a minute" EX 60

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 Redict.

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"get",KEYS[1]) == ARGV[1]
    return 0

The script should be called with EVAL ...script... 1 resource-name token-value

History #

Added the `EX`, `PX`, `NX` and `XX` options.
Added the `KEEPTTL` option.
Added the `GET`, `EXAT` and `PXAT` option.
Allowed the `NX` and `GET` options to be used together.

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