Apache Accumulo Shard Example

Accumulo has an iterator called the intersecting iterator which supports querying a term index that is partitioned by document, or “sharded”. This example shows how to use the intersecting iterator through these four programs:

  • Index.java - Indexes a set of text files into an Accumulo table
  • Query.java - Finds documents containing a given set of terms.
  • Reverse.java - Reads the index table and writes a map of documents to terms into another table.
  • ContinuousQuery.java - Uses the table populated by Reverse.java to select N random terms per document. Then it continuously and randomly queries those terms.

To run these example programs, create two tables like below.

username@instance> createnamespace examples
username@instance> createtable examples.shard
username@instance examples.shard> createtable examples.doc2term

After creating the tables, index some files. The following command indexes all of the java files in the Accumulo source code.

$ find /path/to/accumulo/core -name "*.java" | xargs ./bin/runex shard.Index -t examples.shard --partitions 30

The following command queries the index to find all files containing ‘foo’ and ‘bar’.

$ ./bin/runex shard.Query -t examples.shard foo bar

In order to run ContinuousQuery, we need to run Reverse.java to populate doc2term.

$ ./bin/runex shard.Reverse --shardTable examples.shard --doc2Term examples.doc2term

Below ContinuousQuery is run using 5 terms. So it selects 5 random terms from each document, then it continually randomly selects one set of 5 terms and queries. It prints the number of matching documents and the time in seconds.

$ ./bin/runex shard.ContinuousQuery --shardTable examples.shard --doc2Term examples.doc2term --terms 5
[public, core, class, binarycomparable, b] 2  0.081
[wordtodelete, unindexdocument, doctablename, putdelete, insert] 1  0.041
[import, columnvisibilityinterpreterfactory, illegalstateexception, cv, columnvisibility] 1  0.049
[getpackage, testversion, util, version, 55] 1  0.048
[for, static, println, public, the] 55  0.211
[sleeptime, wrappingiterator, options, long, utilwaitthread] 1  0.057
[string, public, long, 0, wait] 12  0.132