Hadoop and Distributed Computing at Yahoo!

Hadoop 0.17 Preview

April 28, 2008

Apache Hadoop 0.17 is due for release any day now. Feature freeze for the release was on April 4th. The Hadoop dev community is currently actively fixing blocking issues discovered by users that have tried it out. This is a release we’re very excited about as it introduces many long awaited performance fixes to the platform. We’ve observed on the order of 30%(!) improvement in the runtime of some of the Hadoop benchmarks. As always, user feedback is invaluable and we urge folks to kick the tires on the release and help close it out. Here is a quick rundown of the important changes in the release.

HDFS

 

• Syntax cleanup of Hadoop fs shell commands
  The syntax of many Hadoop fs shell commands has been revised. The goals have syntax consistency across commands and compatibility with POSIX syntax as far as possible. For examples, see HADOOP-1677, HADOOP-1792, HADOOP-1891
• Block placement changes
  HDFS’ block placement strategy is now more tuned towards evenly distributing data across nodes. When a block is written from a node that is not running a Datanode, the first replica is written to a node on the same switch as the writer (instead of being written to the same node as the writer). The remaining two replicas are written to two nodes on a different switch. This strategy produces substantially better distributions in cases where data is loaded into HDFS from a small number of machines. More details at HADOOP-2559.
• Append... getting closer
  Everyone’s favorite bug, HADOOP-1700, is still not closed, but a lot of progress has been made in this release. Append related work will make possible new flush() and sync() methods in the HDFS interface. The semantics are familiar. The flush() call plonks data into the ‘system buffers’ and returns immediately. The sync() call writes the data to the system, and returns only when it has hit disk.
• More efficient replication
  Losing a rack of nodes usually means that the Namenode has to replicate around half a million blocks, and quickly. This would cause Namenode responsiveness to degrade and would increase the risk of data loss. A faster replication scheduling algorithm in the Namenode enables it to maintain quality of service to clients and replicate data faster in the event of losing many nodes at once.

Map/Reduce

 

• Switch awareness
  Hadoop map/reduce is now capable of switch aware task placement. The framework attempts to place tasks on machines where their input data resides. In many cases (in particular with HoD), machines with input data are not available for running tasks, but machines that share a switch with such ‘input nodes’ are. Hadoop will now attempt to place tasks on machines that are switch local to input when machines with input data are unavailable.
• Faster task scheduling
  HADOOP-2119 removes many inefficiencies in task placement and scheduling logic. The JobTracker would perform linear scans of the list of submitted tasks in cases where it did not find an obvious candidate task for a node. With better data structures for managing job state, all task placement operations now run in constant time.
• Sort and shuffle improvements
  A couple of significant improvements to sort and shuffle are included in the form of HADOOP-910 and HADOOP-2919. HADOOP-910 has reducers performing merges of shuffle data (both in memory and on disk) while fetching map outputs. HADOOP-2919 improves memory management in sort on the map side, substantially decreases setup cost for the sort and uses quicksort instead of mergesort as the sorting algorithm.

Sameer Paranjpye
Yahoo! Grid Computing Team

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VIM Color Syntax Highlighting for Pig

April 25, 2008

I joined the Yahoo! Research Engineering group a few weeks ago, and I was literally blown away with the possibilities that Hadoop and Pig open for me. Immediately, I wanted to hack up something good to say thank you to all smart people that build and support such a great software.

I am convinced that Pig deserves more respect from the major text editors, so I wrote a small vim script that adds syntax highlighting for Pig files.

You can download it from vm.org site.

To install, follow instructions on the web page, and don't forget to vote! :-)

Emacs version is coming up soon (yes, I use both vim *and* emacs). It will be my project for the upcoming Yahoo! Hack Day.

Sergiy Matusevych
Yahoo! Research Engineer

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Hadoop Summit Slides and Video Available

April 18, 2008

It's been a few weeks since the Hadoop Summit in Santa Clara, and we hope everyone had a good time and learned a lot. Feedback has been quite good so far, but don't be shy about sending us comments.

The Yahoo! Research team has assembled a single page containing links to all the presentation slides and video from both the Hadoop Summit and the Data Intensive Computing Symposium.

As a sample, here's the opening presentation that Doug and Eric gave:

Update: Videos are currently unavailable outside of Yahoo! We're working on the problem...

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More Hadoop Summit Seats Available! New Venue too.

March 12, 2008

To say that we've been surprised by the interest in attending the Hadoop Summit would be an understatement. We already expanded the capacity once and that filled up in a matter of hours. And that pretty much maxed out the event budget and parking too.

So last week when our friends at Amazon Web Services got in touch to see if they could help, we started working on a plan to make the event even larger while still keeping it free. Before long, we'd hatched a plan that involved moving off-site to a nearby venue, more food, more T-shirts, and some minor schedule tweaking.

But most importantly, we have room for about 75 more people!

As of now, we've increased the capacity of the event on Upcoming.org. If you're been watching and waiting to get on the liste of attendees, the time is now.

The new venue is the Network Meeting Center which is located in Santa Clara, California.

Thanks to Amazon.com for buying everyone lunch during the summit. :-)

We'll be updating the agenda soon to include Jinesh from Amazon who will discuss GrepTheWeb - Hadoop on AWS. As you may know, Amazon has many customers running Hadoop on EC2.

If you cannot attend, we're still planning to record all the talks and put them on-line within a week after the summit date.

See you at the summit!

See Also: Hadoop Summit also scaled on-demand! on the Amazon Web Services blog.

Jeremy Zawodny
Yahoo! Developer Network

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An Introduction to ZooKeeper Video

March 7, 2008

A few weeks ago, I had the chance to capture video of a presentation given by Benjamin Reed from Yahoo! Research. His presentation was an introduction to ZooKeeper, a highly available and reliable coordination system built by Yahoo! Research and released under the Apache License, Version 2.0.

Preparing to post the video, I asked Ben for a a summary of the motivations for building ZooKeeper. Here's what he had to say:

In 2006 we were building distributed applications that needed a master, aka coordinator, aka controller to manage the sub processes of the applications. It was a scenario that we had encountered before and something that we saw repeated over and over again inside and outside of Yahoo!.

For example, we have an application that consists of a bunch of processes. Each process needs be aware of other processes in the system. The processes need to know how requests are partitioned among the processes. They need to be aware of configuration changes and failures. Generally an application specific central control process manages these needs, but generally these control programs are specific to applications and thus represent a recurring development cost for each distributed application. Because each control program is rewritten it doesn't get the investment of development time to become truly robust, making it an unreliable single point of failure.

We developed ZooKeeper to be a generic coordination service that can be used in a variety of applications. The API consists of less than a dozen functions and mimics the familiar file system API. Because it is used by many applications we can spend time making robust and resilient to server failures. We also designed it to have good performance so that it can be used extensively by applications to do fine grained coordination.

We have found ZooKeeper to be applicable to many distributed applications inside of Yahoo! and expect it to be applicable to many more outside of Yahoo! For that reason we released it as open source under the Apache license. If you are writing a distributed application, ZooKeeper can help.

And here's the video...

download (m4v)

A PDF copy of the slides is available too.

While filming his 1 hour presentation, I found myself really wishing that ZooKeeper was available 6 or 7 years ago when I was struggling with how to perform distributed processing of news feeds for Yahoo! Finance. ZooKeeper is clearly a more elegant solution than the hack we put together!

Ben will be speaking about ZooKeeper later this month at the Hadoop Summit.

More videos are available on YDN Theater.

Jeremy Zawodny
Yahoo! Developer Network

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Hadoop Summit Nearly Full! We'll Webcast and Post Video...

February 28, 2008

We've been quite impressed by the overwhelming interest in the upcoming Hadoop Summit in late March. Over 150 people have marked themselves as attending or watching on Upcoming.org.

In fact, we hit our attendance cap a mere 36 hours after announcing the event. So there's clearly a lot of interest in the program. As a result, we're opening up more slots today.

We're going to do our best to make as much of the proceedings available on-line as quickly as possible. We'd already planned to make high quality video recordings of all the talks available on YDN Theather a week or so after the event.

Now we're also looking at ways to open it up during the event as well. Expect to see a live webcast and a live chat room so that you can ask questions and chat with those who are physically in Sunnyvale, California for the summit. Once all the details are nailed down, we'll post on the Hadoop blog and on the Hadoop Summit site as well.

We could use IRC, Yahoo! Live, or other options. If you have an opinion, drop a note in the comments.

Thanks for all the interest! This is an exciting time for Hadoop.

Jeremy Zawodny
Yahoo! Developer Network

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