Saturday 28 August 2010

Behemoth talk from BerlinBuzzwords 2010

The talk I gave on Behemoth at BerlinBuzzwords has been filmed (I do not dare watching it) and is available on

The slides can be found on

The talk contains a quick demo of GATE and mentions Tika, UIMA and of course Hadoop.

Friday 27 August 2010

Tom White on Hadoop 0.21

An excellent summary from Tom White on the release 0.21 of Hadoop

Having the distributed cache and parallel mappers with the LocalJobRunner is very good news for Behemoth as we need it to distribute the resources to all the nodes. This should make it easier to test in local mode.

Thursday 26 August 2010

Using Payloads with DisMaxQParser in SOLR

Payloads are a good way of controlling the scores in SOLR/Lucene.

This post by Grant Ingersoll gives a good introduction to payloads, I also found pretty useful. 

What I will describe here is how to use the payloads and have the functionalities of the DisMaxQParser in SOLR.

SOLR already has a field type for analysing payloads 

and we can also define a custom Similarity to use with the payloads

then specify this in the SOLR schema

<!-- schema.xml -->
<similarity class="" />

So far so good. We now need a QueryParser plugin in order to use the payloads in the search and as mentioned above, I want to keep the functionalities of the DisMaxQueryParser.
The problem is that we need to specify PayloadTermQuery objects instead of TermQueries which is down deep in the object hierarchies and cannot AFAIK be modified simply from DismaxQueryParser.
I have implemented a modified version of DismaxQueryParser which rewrites the main part of the query (a.k.a userQuery in the implementation) and substitutes the TermQueries with PayloadTermQueries.
First we'll create a QParserPlugin 

which does not do much but simply exposes the PLDisMaxQueryParser which is a modified version of the standard DisMaxQueryParser but with PayloadQuery objects.

Once these 3 classes have been compiled, jarred and put in the classpath of SOLR, we must add 

 to solrconfig.xml.
then specify for the requestHandler : 
<str name="defType">payload</str>
<!-- plf : comma separated list of field names --> 
 <str name="plf">
The fields listed in the parameter plf will be queried with Payload query objects.  Remember that you can use &debugQuery=true to get the details of the scores and check that the payloads are being used.

Thursday 19 August 2010

Tika on FeatherCast

Apache Tika recently split off from the Lucene project and became a separate top level Apache project. Chris Mattmann is talking about what Tika is, and where it’s going on

Friday 13 August 2010

Towards Nutch 2.0

Nevermind the dodgy look of the blog - I'll improve that later!

For my first post, I'd like to mention the progress we've made recently towards Apache Nutch 2.0. It is based on a branch named NutchBase which has been developed mainly by Doğacan Güney and it is now in the trunk of the SVN repository. One of the main aspects of Nutch 2.0 is that it is now storing its data in a datastore and not in Hadoop's file-based structures. Note that we still have the distribution and replication of the data over a whole cluster and data locality for MapReduce but we also have the possibility to insert or modify a random entry in the table without having to read/write the whole data structure as it was the case before.

Nutch uses a project named GORA as an intermediate between our code and the backend storage. There would be a lot of things to say on GORA but to make it short what we are trying to achieve with it is to make it a sort of common API for NoSQL stores. GORA already has implementations for HBase and Cassandra but also SQL. The plan for GORA is to put it in the Apache Incubator or possibly as an Apache subproject (Hadoop? HBase? Cassandra?). We'll see how it goes.

There are quite a few structural changes in Nutch, most notably the fact that there aren't any segments any more as all the information about a URL (metadata, original content, extracted text, ...) in stored in a single table which means for instance no more segments to merge or metadata to move back to the crawldb. It's all in one place!

There are other substantial changes in 2.0, notably the removal of the Lucene-based indexing and search as we now rely on SOLR. Other indexing backends might be added later. Another step towards delegating functionalities to external projects is the increased used of Apache Tika for the parsing. We've removed quite a few legacy parsers from Nutch and let Tika do the work for us. We've also revamped the organisation of the code and did a lot of code clean up.

Nutch 2.0 is still at an early stage and we are actively working on it, testing, debugging etc... The good news is that it is not only an architectural change but also a basis for a whole lot of new functionalities (see for instance

I'll keep you posted on our progress, as usual : give it a try, get involved, join us...