New string enhancement commands for Tair instances - Tair (Redis® OSS-Compatible)

This topic describes the new CAS and CAD commands for Tair instances, which enhance Redis string functionality.

Prerequisites

The instance is a Tair DRAM-based or persistent memory-optimized instance whose minor version is 1.2.3 or later.

Note

The latest minor version provides more features and higher stability. We recommend that you update the instance to the latest minor version. For more information, see Update the minor version of an instance. If your instance is a cluster instance or read/write splitting instance, we recommend that you update the proxy nodes in the instance to the latest minor version to ensure that all commands can be run as expected.

Usage notes

The commands in this topic apply to native Redis strings.

Note

A Tair instance can contain both Redis strings and TairStrings. The commands in this topic do not apply to TairStrings.

Command list

Table 1. String enhancement commands

Command	Syntax	Description
CAS	`CAS key oldvalue newvalue [EX\|PX\|EXAT\|PXAT time]`	CAS (Compare And Set) checks if the value of a target key is equal to the specified oldvalue. If they are equal, the command updates the value to the new newvalue. Otherwise, the command does nothing. Note This command applies only to Redis strings. To perform the same operation on TairStrings, use the EXCAS command.
CAD	`CAD key value`	CAD (Compare And Delete) checks if the value of a target key is equal to the specified value. If they are equal, the command deletes the key. Otherwise, the command does nothing. Note This command applies only to Redis strings. To perform the same operation on TairStrings, use the EXCAD command.

Note

The following list describes the conventions for the command syntax used in this topic:

Uppercase keyword: indicates the command keyword.
Italic text: indicates variables.
[options]: indicates that the enclosed parameters are optional. Parameters that are not enclosed by brackets must be specified.
A|B: indicates that the parameters separated by the vertical bars (|) are mutually exclusive. Only one of the parameters can be specified.
...: indicates that the parameter preceding this symbol can be repeatedly specified.

CAS

Item	Description
Syntax	`CAS key oldvalue newvalue [EX\|PX\|EXAT\|PXAT time]`
Time complexity	O(1)
Command description	CAS (Compare And Set) checks if the value of a target key is equal to the specified oldvalue. If they are equal, the command updates the value to the new newvalue. Otherwise, the command does nothing. Note This command applies only to Redis strings. To perform the same operation on TairStrings, use the EXCAS command.
Options	Key: The target key of the string type. oldvalue: The original value to compare with the current value of the key. newvalue: The new value. If `oldvalue` is equal to the current value of the key, the value is updated to `newvalue`. EX: Sets the relative expiration time of the key in seconds. A value of 0 means the key expires immediately. If you do not specify this parameter, the key does not expire. EXAT: Sets the absolute expiration time of the key as a UNIX timestamp in seconds. A value of 0 means the key expires immediately. If you do not specify this parameter, the key does not expire. PX: Sets the relative expiration time of the key in milliseconds. A value of 0 means the key expires immediately. If you do not specify this parameter, the key does not expire. PXAT: Sets the absolute expiration time of the key as a UNIX timestamp in milliseconds. A value of 0 means the key expires immediately. If you do not specify this parameter, the key does not expire. Note If the original string has a Time to Live (TTL) set, running the CAS command without a TTL parameter removes the TTL. The key will then not expire.
Return value	1: The operation was successful. 0: The operation failed. -1: The key does not exist. In other cases, an error message is returned.
Example	Run the `SET foo bar` command first. Sample command: `CAS foo bar bzz EX 10` Sample return value: `(integer) 1` If you then run the `GET foo` command, `"bzz"` is returned.

CAD

Item	Description
Syntax	`CAD key value`
Time complexity	O(1)
Command description	CAD (Compare And Delete) checks if the value of a target key is equal to the specified value. If they are equal, the command deletes the key. Otherwise, the command does nothing. Note This command applies only to Redis strings. To perform the same operation on TairStrings, use the EXCAD command.
Options	Key: The target key of the string type. value: The value to compare with the current value of the key.
Return value	1: The operation was successful. 0: The operation failed. -1: The key does not exist. In other cases, an error message is returned.
Example	Run the `SET foo bar` command first. Sample command: `CAD foo bar` Sample return value: `(integer) 1` The foo key is deleted. If you then run the `GET foo` command, `(nil)` is returned.