@makerbot/redis-scan NPM

Node Redis key scanner

Adds support for cancellation. Based off the library by GigSalad.

A simple ES6 Redis key scanner for Node 8 and newer. This is a small class that allows you to do one thing quickly and easily: scan a Redis keyspace for a given pattern.

See the Redis SCAN command documentation for information about how to write patterns for matching, the guarantees, caveats, etc.

Install

yarn add node-redis-scan

Use

Instantiate this class with a Node Redis client and then perform keyspace scans in one of two ways...

The `scan()` method

The scan() method provides the easiest way to scan your keyspace with a single callback that will be passed all matching keys. Depending on the size of your keyspace (millions of keys and beyond) this process might take many seconds or longer.

Parameters

Name	Type	Description
`pattern`	string	The Redis glob-style string pattern to match keys against.
`callback`	function	Invoked with (err, matchingKeys).

Example

const redis = require('redis');
const redisScan = require('node-redis-scan');

const client = redis.createClient();
const scanner = new redisScan(client);

scanner.scan('some-pattern*', (err, matchingKeys) => {
    if (err) throw(err);

    // matchingKeys will be an array of strings if matches were found
    // otherwise it will be an empty array.
    console.log(matchingKeys);
});

The `eachScan()` method

The eachScan() method is useful if you want to perform work with matched keys at the same time as the keyspace is being scanned. When you’re scanning an enormous keyspace this is likely a more efficient way to operate: you can begin handling matched keys asynchronously, before the scan has finished. Unfortunately this approach doesn’t help in situations where you need to have every matching key prior to performing the next step in your operation/application.

Matching keys are passed to the intermediate callback function after each iteration of the Redis SCAN command. The final callback is passed a count of how many matching keys were returned.

Parameters

Name	Type	Description
`pattern`	string	The Redis glob-style string pattern to match keys against.
`eachScanCallback`	function	Invoked with (matchingKeys). If this returns `true` (NOT truthy), the scan will be cancelled. Useful if you only want to scan until a key is found.
`callback`	function	Invoked with (err, matchCount).

Example

const redis = require('redis');
const redisScan = require('node-redis-scan');

const client = redis.createClient();
const scanner = new redisScan(client);

scanner.eachScan('some-pattern*', (matchingKeys) => {
    // Depending on the pattern being scanned for, many or most calls to
    // this function will be passed an empty array.
    if (matchingKeys.length) {
        // matchingKeys found after this iteration of the SCAN command.
        console.log(matchingKeys);
    }
}, (err, matchCount) => {
    if (err) throw(err);

    // matchCount will be an integer count of how many total keys
    // were found and passed to the intermediate callback.
    console.log(`Found ${matchCount} keys.`);
});