Apache Con – Wrap up

2010-11-29 23:27
After one week of lots of interesting input the ASF's user conference was over. With a focus on Apache software users quite a few talks are not too well suited for conference regulars but more or less targeted at newbies who want to know who too successfully apply the software. As a developer of Mahout with close ties to the Lucene and Hadoop community what is of course most interesting to me are stories of users putting the software into production.
The conference was well organised: The foundation features way more projects at the moment than can reasonably be covered in just one conference. As a result Apache Con only covers only a subset of what is being developed at Apache. As such more and more smaller community organised events are being run by individuals as well as corporations. Still Apache Con is a nice place to get in touch with other developers – and to get a glimpse of what is going on in project outsides ones own regular community.

Teddy in Atlanta

2010-11-28 23:24
While I was happily attending Apache Con US in Atlanta/GA my teddy had a closer look at the city: He first went to the centennial olympic park, took a picture of the world of coca-cola (wondering what strange kinds of museums there are in the US.

After that he headed over to Midtown having a quiet time in the Piedmont park. And finally had a closer look at the private houses still decorated for Halloween. Seems like it was squirrel day that day: Met more than ten squirrels he told me.

I found quite some impressive pictures of the arts museum on my camera after his trip out – as well as several images taken at the campus of the Georgia tech university. It's amazing to see what facilities are available to students – especially compared to the equipment of German universities.

Apache Con – Hadoop, HBase, Httpd

2010-11-24 23:19
The first Apache Con day featured several presentations on NoSQL databases (track sponsored by Day software), a Hadoop track as well as presentations on Httpd and an Open source business track.

Since its inception Hadoop always was intended to be run in trusted environments firewalled from hostile users or even attackers. As such it never really supported any security features. This is about the change with the new Hadoop release including better Kerberos based security.

When creating files in Hadoop a long awaited feature was append support. Basically up to now writing to Hadoop was a one-of job: Open a file, write your data, close it and be done. Re-opening and appending data was not possible. This situation is especially bad for HBase as its design relies on being able to append data to an existing file. There have been efforts for adding append support to HDFS earlier as well as an integration of such patches by third party vendors. However only with a current Hadoop version Append is officially supported by HDFS.

A very interesting use case-wise of the Hadoop stack was presented by $name-here from $name. They are using a Hadoop cluster to provide a repository of code released under free software licenses. The business case is to enable corporations to check their source code against existing code and spot license infringements. This does not only include linking to free software under incompatible licenses but also developers copying pieces of free code, e.g. copying entire classes or functions into internal projects that originally were available only under copyleft licenses.

The speaker went into some detail explaining the initial problems they had run into: Obviously it's no good idea to mix and match Hadoop and HBase versions freely. Instead it is best practice to use only versions claimed to be compatible by the developers. Another common mistake is to leave parameters of both projects at their defaults. The default parameters are supposed to be fool-proof. However they are optimised to work well for Hadoop newbies who want to try out the system on a single node cluster and in a distributed setting obviously need more attention. Other anti-patterns include storing only tiny little files in the cluster thus quickly running out of memory on the namenode (that stores all file information including block mappings in main memory for faster access).

In the NoSQL track Jonathan Grey from Facebook gave a very interesting overview on the current state of HBase. Turns out that Facebook would announce only a few days after that their internal use of HBase for the newly launched feature of Facebook messaging.

HBase has adopted a release cycle including development/ production releases to get their systems into interested users' hands more quickly: Users willing to try out new experimental features can use the development releases of HBase. Those who are not should go for the stable releases.

After focussing on improving performance in the past months the project is currently focussing on stability: Data loss is to be avoided by all means. Zookeeper is to be integrated more tightly for storing configuration information thus enabling live reconfiguration (at least to some extend). In addition also HBase is targeting to integrate stored procedures like behaviour: As explained in Googles Percolator paper $LINK batch oriented processing get's you only so far. If data that gets added constantly it makes sense to give up on some of the throughput batch-based systems provide and instead optimise for shorter processing cycles by implementing event triggered processing.

On recommendation of one of neofonie's sys-ops I visited some of the httpd talks: First Rich Bowen gave an overview of unusual tasks one can solve with httpd. The list included things like automatically re-writing http response content to match your application. There is even a spell checker for request URLs: Given marketing has given your flyer to the press with a typo in the url, chances are that the spellchecking module can fix these automatically for each request: Common mistakes covered are switched letters, numbers replaced by letters etc. The performance cost has to be paid only in case no hit could be found – so instead of returning a 404 right away the server first tries to find the document by taking into account common mis-spellings.