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Hadoop tools for manipulating ClueWeb collections
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README.md

ClueWeb Tools

Hadoop tools for manipulating ClueWeb collections, the most recent of which is ClueWeb12 collection.

Sign up to the mailing list at the clueweb-list@cwi.nl mailman page.

Getting Stated

You can clone the repo with the following command:

$ git clone git://github.com/lintool/clueweb.git

Once you've cloned the repository, build the package with Maven:

$ mvn clean package appassembler:assemble

Two notes:

  • appassembler:assemble automatically generates a few launch scripts for you.
  • in addition to the normal jar (clueweb-tools-0.X-SNAPSHOT.jar), this package uses the Maven Shade plugin to create a "fat jar" (clueweb-tools-0.X-SNAPSHOT-fatjar.jar) that includes all dependencies except for Hadoop, so that the jar can be directly submitted via hadoop jar ....

To automatically generate project files for Eclipse:

$ mvn eclipse:clean
$ mvn eclipse:eclipse

You can then use Eclipse's Import "Existing Projects into Workspace" functionality to import the project.

Counting Records

For sanity checking and as a "template" for other Hadoop jobs, the package provides a simple program to count WARC records in ClueWeb12:

hadoop jar target/clueweb-tools-0.X-SNAPSHOT-fatjar.jar \
 org.clueweb.clueweb12.app.CountClueWarcRecords -input /path/to/warc/files/

Examples of /path/to/warc/files/ are:

  • /data/private/clueweb12/Disk1/ClueWeb12_00/*/*.warc.gz: for a single ClueWeb12 segment
  • /data/private/clueweb12/Disk1/ClueWeb12_*/*/*.warc.gz: for an entire ClueWeb12 disk
  • /data/private/clueweb12/Disk[1234]/ClueWeb12_*/*/*.warc.gz: for all of ClueWeb12

Building a Dictionary

The next step is to build a dictionary that provides three capabilities:

  • a bidirectional mapping from terms (strings) to termids (integers)
  • lookup of document frequency (df) by term or termid
  • lookup of collection frequency (cf) by term or termid

To build the dictionary, we must first compute the term statistics:

hadoop jar target/clueweb-tools-0.X-SNAPSHOT-fatjar.jar \
 org.clueweb.clueweb12.app.ComputeTermStatistics \
 -input /data/private/clueweb12/Disk1/ClueWeb12_00/*/*.warc.gz \
 -output term-stats/segment00

By default, the program throws away all terms with df less than 100, but this parameter can be set on the command line. The above command compute term statistics for a segment of ClueWeb12. It's easier to compute term statistics segment by segment to generate smaller and more manageable Hadoop jobs.

Compute term statistics for all the other segments in the same manner.

Next, merge all the segment statistics together:

hadoop jar target/clueweb-tools-0.X-SNAPSHOT-fatjar.jar \
 org.clueweb.clueweb12.app.MergeTermStatistics \
 -input term-stats/segment* -output term-stats-all

Finally, build the dictionary:

hadoop jar target/clueweb-tools-0.X-SNAPSHOT-fatjar.jar \
 org.clueweb.clueweb12.app.BuildDictionary \
 -input term-stats-all -output dictionary -count 7160086

You need to provide the number of terms in the dictionary via the -count option. That value is simply the number of output reducers from MergeTermStatistics.

To explore the contents of the dictionary, use this little interactive program:

hadoop jar target/clueweb-tools-0.X-SNAPSHOT-fatjar.jar \
 org.clueweb.clueweb12.dictionary.DefaultFrequencySortedDictionary dictionary

On ClueWeb12, following the above instructions will create a dictionary with 7,160,086 terms.

Implementation details: Tokenization is performed by first using Jsoup throw away all markup information and then passing the resulting text through Lucene's StandardAnalyzer.

The dictionary has two components: the terms are stored as a front-coded list (which necessarily means that the terms must be sorted); a monotone minimal perfect hash function is used to hash terms (strings) into the lexicographic position. Term to termid lookup is accomplished by the hashing function (to avoid binary searching through the front-coded data structure, which is expensive). Termid to term lookup is accomplished by direct accesses into the front-coded list. An additional mapping table is used to convert the lexicographic position into the (df-sorted) termid.

Building Document Vectors

With the dictionary, we can now convert the entire collection into a sequence of document vectors, where each document vector is represented by a sequence of termids; the termids map to the sequence of terms that comprise the document. These document vectors are much more compact and much faster to scan for processing purposes.

The document vector is represented by the interface org.clueweb.data.DocVector. Currently, there are two concrete implementations:

  • VByteDocVector, which uses Hadoop's built-in utilities for writing variable-length integers (what Hadoop calls VInt).
  • PForDocVector, which uses PFor compression from Daniel Lemire's JavaFastPFOR package.

To build document vectors, use either BuildVByteDocVectors or BuildPForDocVectors:

hadoop jar target/clueweb-tools-0.X-SNAPSHOT-fatjar.jar \
 org.clueweb.clueweb12.app.Build{VByte,PFor}DocVectors \
 -input /data/private/clueweb12/Disk1/ClueWeb12_00/*/*.warc.gz \
 -output /data/private/clueweb12/derived/docvectors/segment00 \
 -dictionary /data/private/clueweb12/derived/dictionary \
 -reducers 100

Once again, it's advisable to run on a segment at a time in order to keep the Hadoop job sizes manageable. Note that the program run identity reducers to repartition the document vectors into 100 parts (to avoid the small files problem).

The output directory will contain SequenceFiles, with a Text containing the WARC-TREC-ID as the key. For VByte, the value will be a BytesWritable object; for PFor, the value will be an IntArrayWritable object.

To process these document vectors, either use ProcessVByteDocVectors or ProcessPForDocVectors in the org.clueweb.clueweb12.app package, which provides sample code for consuming these document vectors and converting the termids back into terms.

Size comparisons, on the entire ClueWeb12 collection:

  • 5.54 TB: original compressed WARC files
  • 1.08 TB: repackaged as VByteDocVectors
  • 0.86 TB: repackaged as PForDocVectors
  • ~1.6 TB: uncompressed termids (collection size is ~400 billion terms)

License

Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0

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