Wednesday 10 November 2010

Gora in incubation at Apache

Great news! GORA has been accepted in the Apache Incubator in September. It now has a brand new site, JIRA, wiki, subversion repository etc... As I explained in my very first post, GORA has been developed as a part of Nutch 2.0 to provide an abstract storage layer. Think about it as a ORM that can be plugged into a number of storage backends (Cassandra, Hbase, Mysql, etc...). What we also get from it is the ability to use these backends directly into Hadoop's MapReduce without having to write any custom code. Another way of looking at it is that it provides a simple and unified API over these various backends. This would allow for instance to develop a prototype using say, MySQL as a backend then switch to Cassandra when more scalability is needed. Since your application would be based on GORA you would not need to modify any of your code, but just the mapping schema (which is based on Apache Avro).

I was thinking about using HBase in Behemoth to avoid having multiple SequenceFiles but GORA would be a better solution as it would give us more options as to what backend to use. On top of that, we would be able to operate at an atomic level and not by batches only, i.e. process a single document from the store and put it back to the DB. Since Behemoth currently relies on the Hadoop data structures, we can only process a whole corpus and generate a new version as output, which is exactly why we wanted to have GORA in Nutch (imagine you have a 10+ billion crawlDB and add say 10M pages per fetch round - every update step in Nutch 1.x requires to read 1010M entries and write out between 1000 and 1010M; a bit wasteful isn't it? )

Assuming that we use GORA (and the AVRO schema for the Behemoth documents), we could then implement a custom Datastore in GATE to debug a Behemoth corpus or test a GATE application.

Now that GORA is in Apache-land, it will hopefully get more contributors involved and more back ends supported.