Cassandra/Hadoop Integration

Cassandra/Hadoop Integration
OLTP + OLAP = Cassandra

BigTable + Dynamo
Semi-structured data model
Decentralized – no special roles, no SPOF
Horizontally scalable
Ridiculously fast writes, fast reads
Tunably consistent
Cross-DC capable
Cassandra (basic overview)

Design your data model based on your query model
Real-time ad-hoc queries aren’t viable
Secondary indexes help
What about analytics?
Querying with Cassandra

Hadoopbrings analytics
MapReduce
Pig/Hive and other tools built above MapReduce
Configurable data sources/destinations
Many already familiar with it
Active community
Enter Hadoop

Basic Recipe
Overlay Hadoop on top of Cassandra
Separate server for name node and job tracker
Co-locate task trackers with Cassandra nodes
Data nodes for distributed cache
Voilà
Data locality
Analytics engine scales with data
Cluster Configuration

Always tune Cassandra to taste
For Hadoop workloads you might
Have a separate analytics virtual datacenter
Using the NetworkTopologyStrategy
Tune the rpc_timeout_in_ms in cassandra.yaml (higher)
Tune the cassandra.range.batch.size
See org.apache.cassandra.hadoop.ConfigHelper
Cluster Tuning

All-in-one Configuration
JobTracker and NameNode
Each node has Cassandra, a TaskTracker, and a DataNode (for distributed cache)

Separate Analytics Configuration
Separated nodes for analytics
Nodes for real-time random access
A single Cassandra cluster with different virtual data centers

Cassandra specific InputFormat
ColumnFamilyInputFormat
Configuration – ConfigHelper, Hadoop variables
InputSplits over the data – tunable
Example usage in contrib/word_count
MapReduce - InputFormat

OutputFormat
ColumnFamilyOutputFormat
Configuration – ConfigHelper, Hadoopvariables
Batches output – tunable
Don’t have to use Cassandra api
Some optimizations (e.g. ConsistencyLevel.ONE)
Uses Avro for output serialization (enables streaming)
Example usage in contrib/word_count
MapReduce - OutputFormat

Visualizing
Take vertical slices of columns
Over the whole column family

What about languages outside of Java?
Build on what Hadoop uses - Streaming
Output streaming as of0.7.0
Example in contrib/hadoop_streaming_output
Input streaming in progress, hoping for 0.7.2
Hadoop Streaming

Developed at Yahoo!
PigLatin/Grunt shell
Powerful scripting language for analytics
Configuration – Hadoop/Envvariables
Uses pig 0.7+
Example usage in contrib/pig
Pig

LOAD 'cassandra://Keyspace1/Standard1' USING CassandraStorage()
as (key:chararray, cols:bag{col:tuple(name:bytearray, value:bytearray)});
cols = FOREACH rows GENERATE flatten(cols) as (name, value);
words = FOREACH cols GENERATE flatten(TOKENIZE((chararray) value)) as word;
grouped = GROUP words BY word;
counts = FOREACH grouped GENERATE group, COUNT(words) as count;
ordered = ORDER counts BY count DESC;
topten = LIMIT ordered 10;
dump topten;

ColumnFamilyInputFormat
ColumnFamilyOutputFormat
Hadoop Streaming Output
Pig support – Cassandra LoadFunc
Summary of Integration

Raptr.com
Home grown solution -> Cassandra + Hadoop
Query time: hours -> minutes
Pig obviated their need for multi-lingual MR
Speed and ease are enabling
Imagini/Visual DNA
The Dachis Group
US Government (Digital Reasoning)
See http://github.com/digitalreasoning/PyStratus
Users of Cassandra + Hadoop

Hive support in progress (HIVE-1434)
Hadoop Input Streaming (hoping for 0.7.2 - 1497)
Pig Storage Func (CASSANDRA-1828)
Row predicates (pending CASSANDRA-1600)
MapReduce et al over secondary indexes (1600)
Performance improvements (though already good)
Future

Performant OLTP + powerful OLAP
Less need to shuttle data between storage systems
Data locality for processing
Scales with the cluster
Can separate analytics load into virtual DC
Conclusion

About Cassandra
http://www.datastax.com/docs
http://wiki.apache.org/cassandra
Search and subscribe to the user mailing list (very active)
#Cassandra on freenode (IRC)
~150-200+ users from around the world
Cassandra: The Definitive Guide
About Hadoop Support in Cassandra
Check out various <source>/contrib modules: README/code
http://wiki.apache.org/cassandra/HadoopSupport
Learn More

About me:
jeremy.hanna@dachisgroup.com
@jeromatron on Twitter
jeromatron on IRC in #cassandra
Questions

http://lancegatlin.org	8
http://twitter.com	6
https://twitter.com	3
http://trunk.ly	1
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http://www.linkedin.com	1

Cassandra/Hadoop Integration

by Jeremy Hanna

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