I initially complaint about the complexity of installing Mesos when I was playing around with Spark and Shark. However
when I saw the Twitter Mesos and Framework presentation, I understood why Mesos can be disruptive to how you architect applications in a highly distributed manner typical for Cloud Computing.
You can see the presentation here.
The key is that Twitter combined Mesos with Zookeeper, Linux Control Groups and Google’s Protocol Buffers as well as Spark, Storm and Hadoop. This provides them with a way to easily program services that can be scaled to hundreds of mesos nodes, automatically upgraded and restarted in case of failure. Also resource usage can be controlled via the control groups. Zookeeper manages the configuration. Protocol buffers assure efficient communication between nodes. Services can use Spark and Storm for real-time operations and Hadoop for batch. Developers do not have to worry about scaling the services, deploying them to different nodes, etc. This is handled by the Twitter Framework and Mesos master.
There is only one thing to add: “TWITTER PLEASE OPEN SOURCE YOUR TWITTER FRAMEWORK” or in Twitter language: “#mesos please #opensource #twitterfw now @telruptive “…
The website defines Spark as a MapReduce-like cluster computing framework designed to support low-latency iterative jobs. However it would be easier to say that Spark is Hadoop for real-time.
Spark allows you to run MapReduce jobs together with your data on distributed machines. Unlike Hadoop Spark can distributed your data in slices and store it in memory hence your processing and data are co-located in memory. This gives an enormous performance boost. Spark is more than MapReduce however. It offers a new distributed framework on which different distributed computing paradigms can be modelled. Examples are: Hadoop’s Hive => Shark (40x faster than Hive), Google’s Pregel / Apache’s Giraph => Bagel, etc. An upcoming Spark Streaming is supposed to bring real-time streaming to the framework.
The excellent part
Spark is written in Scala and has a very straight forward syntax to run applications from the command line or via compiled code. The possibilities to run iterative operations over large datasets or very compute intensive operations in parallel, make it ideal for big data analytics and distributed machine learning.
The points for improvement
In order to use Spark, you need to install Mesos. Mesos is a framework for distributed computing that was also developed by Berkeley. So in a sense they are eating their own dog food. Unfortunately Mesos is not written in scala so installing Spark becomes a mix of make’s, ant’s, .sh, XML, properties, .conf, etc. It would not be bad if Mesos would have consistent documentation but due to incubation into Apache the installation process is currently undergoing changes and is not straightforward.
Spark allows to connect to Hadoop, Hbase, etc. However running Hadoop on top of Mesos is “experimental” to say the least. The integration with Hadoop should be lighter. At the end only access to HDFS, SequenceFiles, etc. is required. This should not mean that a complete Hadoop should be installed and Spark should be recompiled for each specific Hadoop version.
If Spark wants to become as successful as Hadoop, then they should learn from Hadoop’s mistakes. Complex installation is a big problem because Spark needs to be installed on many machines. The Spark team should take a look at Ruby’s Rubygems, Node.js’s npm, etc. and make the installation simple, ideally via Scala’s package manager, although it is less popular.
If possible the team should drop Mesos as a prerequisite and make it optional. One of Spark’s competitors is Storm & Trident, you can install a Storm cluster in minutes and have a one click command to run Storm on an EC2 cluster.
It would be nice if there would be an integration SDK that allows extensions to be plugged-in. Integrations with Cassandra, Redis, Memcache, etc. could be developed by others. Also looking at a distribution in which Cassandra’s Brisk is used to mimic Hive and HDFS (a.k.a. CassandraFS) and have it all pre-bundled with Shark, could be an option. Spark’s in-memory execution and read speed, combined with Cassandra’s write speed, should make for a pretty quick and scalable solution. Ideally without the need to fight with namenodes, datanodes, jobtrackers, etc. and other Hadoop hard-to-configure inventions…
The conclusion is that distributed computing and programming is already hard enough by itself. Programmers should be focusing on their algorithms and not need a professional admin to get them started.
All-in-all Spark, Shark, Streaming Spark, Bagel, etc. have a lot of potential, it is just a little bit rough around the edges…
Update: I am reviewing my opinion about Mesos. See the Mesos post.
In a previous post I mentioned Storm already. Trident is an extension of Storm that makes it an easy-to-use distributed real-time analytics framework for Big Data. Both Trident and Storm were developed by Twitter.
One of Twitter’s major problems is to keep statistics of Tweets and Tweeted URLs that get retweeted by millions of followers. Imagine a famous person who tweets a URL to millions of followers. Lots of followers will retweet the URL. So how do you calculate how many Tweeters have seen the URL? This is important for features like “Top retweeted URLs”.
The answer was Storm but with the addition of Trident, it has become a lot easier to manage. Trident is doing to Storm what Pig and Cascading are doing to Hadoop: simplification. Instead of having to create a lot of Spouts and Bolts and take care of how messages are distributed, Trident comes with a lot of the work already done.
In a few lines of code, you set-up a Distributed RPC server, send it URLs, have it collect the tweeters and followers and count them. Fail-over and resiliance as well as massive distribution throughput are build into the platform. You can see it in this example code:
TridentState urlToTweeters =
TridentState tweetersToFollowers =
.stateQuery(urlToTweeters, new Fields("args"), new MapGet(), new Fields("tweeters"))
.each(new Fields("tweeters"), new ExpandList(), new Fields("tweeter"))
.stateQuery(tweetersToFollowers, new Fields("tweeter"), new MapGet(), new Fields("followers"))
.each(new Fields("followers"), new ExpandList(), new Fields("follower"))
.aggregate(new One(), new Fields("one"))
.aggregate(new Count(), new Fields("reach"));
The possibilities of Trident + Storm, combined with fast scalable datastores, like for instance Cassandra, are enormous. Everything from real-time counters, filtering, complex event processing, machine learning, etc.
The Storm concept of Spout [data generation] and Bolt [data processing] can be easily understood by most programmers. Storm is an asynchronous highly distributed framework but with a simple distributed RPC server it can easily be used in synchronous code.
The only drawback I have seen is that DRPC is focused only on Strings (and other primitive types that can be contained in a String). Adding more complex objects (via Kryo, Avro, Protocol Buffers, etc.), or at least bytes, would be useful for companies that do not only focus on Tweets.