Stratio Cassandra

Stratio Cassandra is a fork of Apache Cassandra where index functionality has been extended to provide near real time search such as ElasticSearch or Solr, including full text search capabilities and free multivariable search. It is achieved through an Apache Lucene based implementation of Cassandra secondary indexes, where each node of the cluster indexes its own data. Stratio Cassandra is one of the core modules on which Stratio’s BigData platform (SDS) is based.

Index relevance queries allows you to retrieve the n more relevant results satisfying a query. The coordinator node sends the query to each node in the cluster, each node returns its n best results and then the coordinator combines these partial results and gives you the n best of them, avoiding full scan. You can also base the sorting in a combination of fields.

Index filtered queries are a powerful help when analyzing the data stored in Cassandra with MapReduce frameworks as Apache Hadoop or, even better, Apache Spark through Stratio Deep. Adding Lucene filters in the jobs input can dramatically reduce the amount of data to be processed, avoiding full scan.

Any cell in the tables can be indexed, including those in the primary key as well as collections. Wide rows are also supported. You can scan token/key ranges, apply additional CQL3 clauses and page on the filtered results.

Other information including documentation is available at Stratio website.

Features

Stratio Cassandra and its integration with Lucene search technology provides:

• Big data full text search

• Relevance scoring and sorting

• Top-k queries

• Complex boolean queries (and, or, not)

• Near real time search

• CQL3 support

• Wide rows support

• Partition and cluster composite keys support

• Support for indexing columns part of primary key

• Support for searching with key/token clauses

• Support for searching with clauses with ALLOW FILTERING

• Apache Hadoop support compatibility

• Stratio Deep support compatibility

• Self contained distribution

Not yet supported:

• Thrift API

• Legacy compact storage option

• Indexing counter columns

• Columns with TTL

Requirements

• Java >= 1.7 (OpenJDK and Sun have been tested)

• Ant >= 1.8

Building and running

Stratio Cassandra is distributed as a fork of Apache Cassandra, so its building, installation, operation and maintenance is overall identical. To build and run type:

ant
sudo mkdir -p /var/log/cassandra
sudo chown -R `whoami` /var/log/cassandra
sudo mkdir -p /var/lib/cassandra
sudo chown -R `whoami` /var/lib/cassandra
bin/cassandra -f

Now you can do some tests using the Cassandra Query Language:

bin/cqlsh

The Lucene’s index files will be stored in the same directories where the Cassandra’s will be. The default data directory is /var/lib/cassandra/data, and each index is placed next to the SSTables of its indexed column family.

For more details about Cassandra please see its documentation.

Example

We will create the following table to store tweets:

CREATE TABLE tweets (
    id INT PRIMARY KEY,
    user TEXT,
    body TEXT,
    time TIMESTAMP,
    lucene TEXT
);

We have created a column called lucene to link the index queries. This column will not store data. Now you can create a custom Lucene index on it with the following statement:

CREATE CUSTOM INDEX tweets_index ON tweets (lucene)
USING 'org.apache.cassandra.db.index.stratio.RowIndex'
WITH OPTIONS = {
    'refresh_seconds'    : '1',
    'schema' : '{
        fields : {
            id   : {type : "integer"},
            user : {type : "string"},
            body : {type : "text",  analyzer : "org.apache.lucene.analysis.en.EnglishAnalyzer"},
            time : {type : "date", pattern  : "yyyy/MM/dd"}
        }
    }'
};

This will index all the columns in the table with the specified types, and it will be refreshed once per second.

Now, to query the top 100 more relevant tweets where body field contains the phrase "big data gives organizations":

SELECT * FROM tweets WHERE lucene='{
	query : {type:"phrase", field:"body", values:["big","data","gives","organizations"]}
}' limit 100;

To restrict the search for tweets within a certain date range, then you must add to the search a filter as follows:

SELECT * FROM tweets WHERE lucene='{
    filter : {type:"range", field:"time", lower:"2014/04/25", upper:"2014/04/1"},
    query  : {type:"phrase", field:"body", values:["big","data","gives","organizations"]}
}' limit 100;

To refine the search to get only the tweets written by users whose name starts with "a":

SELECT * FROM tweets WHERE lucene='{
    filter : {type:"boolean", must:[
                   {type:"range", field:"time", lower:"2014/04/25", upper:"2014/04/1"},
                   {type:"prefix", field:"user", value:"a"} ] },
    query  : {type:"phrase", field:"body", values:["big","data","gives","organizations"]}
}' limit 100;

To get the 100 more recent filtered results you can use the sort option:

SELECT * FROM tweets WHERE lucene='{
    filter : {type:"boolean", must:[
                   {type:"range", field:"time", lower:"2014/04/25", upper:"2014/04/1"},
                   {type:"prefix", field:"user", value:"a"} ] },
    query  : {type:"phrase", field:"body", values:["big","data","gives","organizations"]},
    sort  : {fields: [ {field:"time", reverse:true} ] }
}' limit 100;

Finally, if you want to restrict the search to a certain token range:

SELECT * FROM tweets WHERE lucene='{
    filter : {type:"boolean", must:[
                   {type:"range", field:"time", lower:"2014/04/25", upper:"2014/04/1"},
                   {type:"prefix", field:"user", value:"a"} ] },
    query  : {type:"phrase", field:"body", values:["big","data","gives","organizations"]}
}' AND token(id) >= token(0) AND token(id) < token(10000000) limit 100;

This last is the basis for Hadoop, Spark and other MapReduce frameworks support.

Please, refer to the comprehensive Stratio Cassandra documentation at Stratio website.