Using Redis SCAN in NODE

问题

I have Redis with a lot of keys in some format and I want to get keys that match some pattern and do some operations on them. I don't use KEYS method since it's not recommend in production. Using SCAN I'm wondering what is the best way to write it in code. I have to do something like a while loop but using promises, my current solution looks like this (code is simplified a little):

'use strict'
const Promise = require('bluebird');
const config = require('./config');
const client = require('./clinet');

let iterator = 0;
Promise.coroutine(function* () {
  do {
    iterator = yield clinet.scanAsync(iterator, 'myQuery', 'COUNT', config.scanChunkSize)
      .then(data => {
        let nextIterator = data[0];
        let values = data[1];
        //do some magic with values
        return nextIterator;
      })
  } while (iterator !== '0');
})();

Is there a better way to do it that I'm missing?

回答1:

You can use recursion to keep calling scan until done.

function scanAsync(cursor, pattern, returnSet){

    return redisClient.scanAsync(cursor, "MATCH", pattern, "COUNT", "100").then(
        function (reply) {

            cursor = reply[0];
            var keys = reply[1];
            keys.forEach(function(key,i){
                returnSet.add(key);
            });

            if( cursor === '0' ){
                return Array.from(returnSet);
            }else{
                return scanAsync(cursor, pattern, returnSet)
            }

    });
}

Pass in a Set() to make sure keys aren't duplicated

myResults = new Set();

scanAsync('0', "NOC-*[^listen]*", myResults).map( 
    function( myResults ){ console.log( myResults); }
);

回答2:

You can try this snippet to scan (1000) keys per iteration and 'delete`.

var cursor = '0';
function scan(pattern,callback){

  redisClient.scan(cursor, 'MATCH',pattern,'COUNT', '1000', function(err, reply){
    if(err){
        throw err;
    }
    cursor = reply[0];
    if(cursor === '0'){
        return callback();
    }else{

        var keys = reply[1];
        keys.forEach(function(key,i){                   
            redisClient.del(key, function(deleteErr, deleteSuccess){
                console.log(key);
            });
        });


        return scan(pattern,callback);
    }
  });
}

scan(strkey,function(){
    console.log('Scan Complete');
});

回答3:

I realize this is a really old question, but I found all of the other answers very unsatisfying. Here is yet another attempt to scan in a relatively clean way using async await (WITHOUT the use of yet another external dependency). You can easily modify this to continuously delete each set of found keys (you would want to tackle them in batches like this in case there are LOTS). Pushing them into an array just demonstrates one very basic thing you could do with them during this stage.

const redis = require('redis');
const { promisify } = require('util');

const client = redis.createClient({...opts});
const scan = promisify(client.scan).bind(client);

const scanAll = async (pattern) => {
  const found = [];
  let cursor = '0';

  do {
    const reply = await scan(cursor, 'MATCH', pattern);

    cursor = reply[0];
    found.push(...reply[1]);
  } while (cursor !== '0');

  return found;
}

回答4:

I think the node bindings for Redis are pushing too much responsibility to the caller here. So I created my own library for scanning as well, using generators in node:

const redis = require('redis')
const client = redis.createClient(…)
const generators = require('redis-async-gen')
const { keysMatching } = generators.using(client)

…

for await (const key of keysMatching('test*')) {
  console.info(key)
}

It's the last bit that obviously is the thing that you should care about. Instead of having to carefully control an iterator yourself, all you need to do is use a for comprehension.

I wrote more about it here.