org.aredis.cache

Class Script

java.lang.Object

org.aredis.cache.Script

All Implemented Interfaces:

Comparable<Script>

public class Script
extends Object
implements Comparable<Script>

A simple immutable holder class to hold a Redis Lua Script and its sha1 digest. A script Object is meant for scripts that are going to be used repeatedly which is normally the case. Ideally scripts should be static variables or Singleton POJOs containing scripts if loaded from a file on jvm start. A Script object is created using the static getInstance method.

A script Object should be used with a RedisCommand.EVALCHECK pseudo command. There is a flag for each Script maintained against each Redis Server. When an AsyncRedisConnection processes an EVALCHECK command for the first time when the flag for the script is not set against the server, it checks if the script is present on the Redis Server by using the SCRIPT EXISTS command on a separate Redis Connection. If SCRIPT EXISTS returns 0 then the script is loaded using the SCRIPT LOAD command. Then the flag for the script is set to indicate that the script is verified/loaded on the server after which an EVALSHA is sent with the script digest as the first parameter. Subsequent EVALCHECK calls for the same script on the same server will straight away translate to EVALSHA since the flag for the script is set against the server.

A script Object can also be used instead of a String to specify the script for the EVAL, EVALSHA, SCRIPT LOAD and SCRIPT EXISTS commands though you do not need these commands if you use the EVALCHECK pseudo-command. The advantage of using a Script Object for these commands in case you have a need to use them is that the script is marked as loaded for the server once the command completes successfully which can be used by the EVALCHECK pseudo command.

This class also includes Script constants containing Scripts used in aredis.

Also note that EVALCHECK commands will start failing if a SCRIPT FLUSH command is executed on the Redis server since the jvm does not know that scripts have been cleared. In such cases the script all script statuses are cleared on detecting the failure and the subsequent EVALCHECK commands will go through.

Author:

Suresh

Field Summary

Fields

Modifier and Type	Field and Description
static Script	ADD_SCRIPT Deprecated. Since version 2.6.12 Redis has an enhanced SET command which has an NX and expiry option. So this script is not required.

Method Summary

Methods

Modifier and Type	Method and Description
int	compareTo(Script o)
boolean	equals(Object o)
int	getIndex() Gets the identifying index of the script.
static Script	getInstance(String s) This static method must be used to create a Script Object.
String	getScript() Gets the script.
String	getSha1sum() Gets the SHA-1 digest of the script.
int	hashCode()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail

ADD_SCRIPT

public static final Script ADD_SCRIPT

Deprecated. Since version 2.6.12 Redis has an enhanced SET command which has an NX and expiry option. So this script is not required.

Though Redis provides a SETNX to atomically add a key if it does not exist, it does not take an expiry time. This Redis Lua script provides an equivalent of memcached add command. It takes a key, an expiry time and a value and atomically sets it with the expiry time if it does not exist. This is used for the lock functionality as well to acquire a distributed lock on a cache server with an expiry time. The lock is considered acquired if the script returns 1.

Method Detail

getInstance

public static Script getInstance(String s)

This static method must be used to create a Script Object.

Parameters:

s - Redis script

Returns:

A script object containing the Redis script and its SHA-1 digest

compareTo

public int compareTo(Script o)

Specified by:

compareTo in interface Comparable<Script>

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

getScript

public String getScript()

Gets the script.

Returns:

Redis script

getSha1sum

public String getSha1sum()

Gets the SHA-1 digest of the script.

Returns:

SHA-1 digest

getIndex

public int getIndex()

Gets the identifying index of the script. Indexes are sequential starting with 0.

Returns:

Script Index