What is sculed?

sculed (SculeJS daemon) is a light-weight server built on top of SculeJS. It allows developers to persist data structures in memory and interact with them remotely via TCP, using a NSSocket based protocol.

The package also includes client libraries that streamline interaction with the server, and make building applications around sculed super simple (and fun).

Data structures currently supported by sculed are:

• Collection
• Hash Table
• Binary Search Tree
• Bloom Filter
• LRU Cache
• LIFO Stack
• Queue
• Counter
• Bit Set

Why would I use this thing?

Why wouldn't you?!

sculed can help with pretty much any task that requires persisting structured data between Node processes - either running on the same machine, or a whole cluster of machines. Any time I need a simple, volatile data store and don't want to go through the hassle of setting up RabbitMQ, MongoDB or MySQL I just spin up a sculed instance and get to work.

Some example applications for sculed:

• Setting up a light-weight queue server to facilitate distributed processing tasks (e.g. web scraping)
• Persisting key/value pairs between Node processes
• Keeping counts of things in memory across different Node processes (e.g. page views, error counts)
• Caching log entries in memory before spooling them out to aggregation services

In terms of performance, sculed does pretty well. Running over loopback I've seen rates of up around 2500 requests p/s for a single connected client (based on self reported statistics from the server). Obviously latency will be higher when traffic between the client and the server is running over an actual network, I'd also expect performance to degrade as concurrency increases.

Examples!

Spooling up a sculed instance is pretty simple. Just check out the code and run the following:

git clone git@github.com:dan-eyles/sculed.git
cd sculed
sudo npm install -g

or

sudo npm install -g sculed

Then to run the server:

sculed -p 72853 --verbose

Setting up a client looks like the following:

var client  = require('lib/client.js');
var structs = {
    counters: {}
};
client.connect('127.0.0.1', 72853, function() {
    structs.jobs = client.getQueue('jobs', null, function(err, data) { /* do something here */ });
});

Once you've established a connection to the sculed instance, you can start working with your data structures. For example, you might have a process running on one machine adding URLs to a queue:

scraper().grab().urls().from('http://some.domain.com', function(err, urls) {
    urls.forEach(function(url) {
        if (!structs.counters.hasOwnProperty(url.domain()) {
            structs.counters[url.domain()] = client.getCounter(url.domain(), [1], function(err, data) { /* do something here */ });
        }
        structs.jobs.enqueue(url);
    });
});

And on a bunch of other machines you might run processes grabbing urls from the queue and doing something with them:

setInterval(function() {
    structs.jobs.dequeue(function(err, url) {
        if (err) {
            /* put some error handling code here */
        }
        if (url === null) {
            return;
        }
        scraper().scrape(url, function(err, data) {
            /* do something with your scraped data here */
        });
        structs.counters[url.domain()].increment(1);
    });
}, 1000);

This example is deceptively simple - you could use sculed to dynamically establish and destroy queues as you need them, without any need for complicated configuration files.

So, what's next?

Over the next couple of months I'm planning on adding the following features to sculed:

• Support for Map/Reduce
• Simple on-disk persistence for data structures and collections
• Support for consistent hashing inside client code (maybe?)
• Support for simple, asynchronous replication of data between sculed instances
• More comprehensive documentation and examples
• Full documentation for the protocol

License yadda yadda yadda

Copyright (c) 2013, Dan Eyles (dan [at] irlgaming [dot] com) All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
• Neither the name of IRL Gaming nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL IRL Gaming BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.