redis-evalsha

Convenience wrapper for Redis EVAL/EVALSHA

npm install redis-evalsha
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shavaluator-js

This library provides a convenient wrapper for sending Lua scripts to a Redis server via EVALSHA.

It works in tandem with mranney/node-redis. Note that node-redis already tries to use evalsha if you use eval. This library merely prevents your code from computing a SHA1 every time you execute a script.

What is EVALSHA?

EVALSHA allows you to send Lua scripts to a Redis server by sending the SHA-1 hashes instead of actual script content. As long as the body of your script was previously sent to Redis via EVAL or SCRIPT LOAD, you can use EVALSHA to avoid the overhead of sending your entire Lua script over the network.

A Shavaluator object wraps a Redis client for executing Lua scripts. When executing Lua scripts, a shavaluator will always attempt EVALSHA first, falling back on EVAL if the script has not yet been cached by the Redis server.

This project was forked from jeffomatic/shavaluator-js for these reasons:

  • simplify the library - 23 files changed, 461 insertions(+), 1211 deletions(-)
  • coffee-script is dumb
  • use redis sendCommand instead of eval method as it tries to be too smart and check the sha that we already computed.
  • ability to use same instance with multiple redis instances

Example

var Shavaluator = require('redis-evalsha')

// 1. Initialize a shavaluator with a Redis client
var shavaluator = new Shavaluator(redis);

// 2. Add a series of named Lua scripts to the shavaluator.
shavaluator.add('delequal',
    "if redis.call('GET', KEYS[1]) == ARGV[1] then\n" +
    "  return redis.call('DEL', KEYS[i])\n" +
    "end\n" +
    "return 0\n");

// 3. The 'delequal' script is now available to call using `exec`. When you
//    call this, first EVALSHA is attempted, and then it falls back to EVAL.
shavaluator.exec('delequal', ['someKey'], ['deleteMe'], function(err, result) {
  console.log(err, result);
});

Adding scripts

Before you can run Lua scripts, you should give each one a name and add them to a shavaluator.

scripts = {
  delequal:
    " \
    if redis.call('GET', KEYS[1]) == ARGV[1] then \
      return redis.call('DEL', KEYS[i]) \
    end \
    return 0 \
    "

  zmembers:
    " \
    local key = KEYS[1] \
    local results = {} \
    if redis.call('ZCARD', key) == 0 then \
      return {} \
    end \
    for i = 1, #ARGV, 1 do \
      local memberName = ARGV[i] \
      if redis.call('ZSCORE', key, memberName) then \
        table.insert(results, memberName) \
      end \
    end \
    return results;
    "
};

for (var name in scripts) {
  shavaluator.add(name, scripts[name]);
}

Adding a script only generates the SHA-1 of the script body; it does not perform any network operations.

Class reference

constructor(redisClient)

add(name, body)

Adds a Lua script to the shavaluator.

exec(scriptName, keysArray, argsArray, callback)

Executes the script named scriptName.

The callback parameter is standard asynchronous callback, taking two arguments:

  1. an error, which is null on success
  2. the script result
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