Hadoop + Cassandra: Fast queries on data lakes, and wikipedia search tutorial

Fast Queries on Data Lakes

Exposing bigdata and streaming analytics using hadoop, cassandra, akka and spray

Natalino Busa@natalinobusa

Big and Fast. Tools Architecture Hands on Application!

Parallelism Hadoop Cassandra Akka

Machine Learning Statistics Big Data

Algorithms Cloud Computing Scala Spray

Natalino Busa@natalinobusa

www.natalinobusa.com

Challenges

Not much time to reactEvents must be delivered fast to the new machine APIsIt’s Web, and Mobile Apps: latency budget is limited

Loads of information to processUnderstand well the user historyAccess a larger context

OK, let’s build some apps

home brewedwikipedia search engine … Yeee ^-^/

Tools of the day:

Hadoop: Distributed Data OS

ReliableDistributed, Replicated File System

Low cost↓ Cost vs ↑ Performance/Storage

Computing Powerhouse

All clusters CPU’s working in parallel for running queries

Cassandra: A low-latency 2D store

ReliableDistributed, Replicated File System

Low latencySub msec. read/write operations

Tunable CAPDefine your level of consistency

Data model: hashed rows, sorted wide columns

Architecture model: No SPOF, ring of nodes, omogeneous system

Lambda architecture

BatchComputing

HTTP RESTful API

In-MemoryDistributed Database

In-memoryDistributed DB’s

Lambda ArchitectureBatch + Streaming

low-latencyWeb API services

StreamingComputing

All Data Fast Data

wikipedia abstracts(url, title, abstract, sections)

hadoopmapper.py

hadoopreducer.py

Publish pages on Cassandra

Produce inverted index entries

Top 10 Urls per word go to Cassandra

How to: Build an inverted index : Apple -> Apple Inc, Apple Tree, The Big Apple

CREATE KEYSPACE wikipedia WITH replication = {'class': 'SimpleStrategy', 'replication_factor': 3};

CREATE TABLE wikipedia.pages ( url text, title text, abstract text, length int, refs int, PRIMARY KEY (url) );

CREATE TABLE wikipedia.inverted ( keyword text, relevance int, url text, PRIMARY KEY ((keyword), relevance) ); Data model ...

memory

disk compute disk

diskcomputedisk

memory

disk diskcompute

memory

disk diskcompute

memory

memory

diskcomputedisk

map (k,v) shuffle & sort reduce (k,list(v))

compute

cat enwiki-latest-abstracts.xml | ./mapper.py | ./reducer.py

Map-Reduce

demystified

./mapper.py

produces tab separated triplets:

element 008930 http://en.wikipedia.org/wiki/Goldwith 008930 http://en.wikipedia.org/wiki/Goldsymbol 008930 http://en.wikipedia.org/wiki/Goldatomic 008930 http://en.wikipedia.org/wiki/Goldnumber 008930 http://en.wikipedia.org/wiki/Golddense 008930 http://en.wikipedia.org/wiki/Goldsoft 008930 http://en.wikipedia.org/wiki/Goldmalleable 008930 http://en.wikipedia.org/wiki/Goldductile 008930 http://en.wikipedia.org/wiki/Gold

Map-Reduce

demistified

./reducer.py

produces tab separated triplets for the same key:

ductile 008930 http://en.wikipedia.org/wiki/Goldductile 008452 http://en.wikipedia.org/wiki/Hydroformingductile 007930 http://en.wikipedia.org/wiki/Liquid_metal_embrittlement...

Map-Reduce

demistified

memory

disk compute disk

diskcomputedisk

memory

disk diskcompute

memory

disk diskcompute

memory

memory

diskcomputedisk

map (k,v) shuffle & sort reduce (k,list(v))

compute

def main(): global cassandra_client

logging.basicConfig() cassandra_client = CassandraClient() cassandra_client.connect(['127.0.0.1']) readLoop() cassandra_client.close()

Mapper ...

doc = ET.fromstring(doc) ...

#extract words from title and abstract words = [w for w in txt.split() if w not in STOPWORDS and len(w) > 2]

#relevance algorithm relevance = len(abstract) * len(links)

#mapper output to cassandra wikipedia.pages table cassandra_client.insertPage(url, title, abstract, length, refs)

#emit unique the key-value pairs emitted = list() for word in words: if word not in emitted: print '%s\t%06d\t%s' % (word, relevance, url) emitted.append(word)

Mapper ...

T split !!!

wikipedia abstracts(url, title, abstract, sections)

hadoopmapper.sh

hadoopreducer.sh

Publish pages on Cassandra

Extract inverted index

Top 10 Urls per word go to Cassandra

Inverted index : Apple -> Apple Inc, Apple Tree, The Big Apple

Export during the

"map" phase

memory

disk compute disk

diskcomputedisk

memory

disk diskcompute

memory

disk diskcompute

memory

memory

diskcomputedisk

map (k,v) shuffle & sort reduce (k,list(v))

computecassandra

cassandra

cassandra

from cassandra.cluster import Cluster

class CassandraClient: session = None insert_page_statement = None

def connect(self, nodes): cluster = Cluster(nodes) metadata = cluster.metadata self.session = cluster.connect() log.info('Connected to cluster: ' + metadata.cluster_name) prepareStatements()

def close(self): self.session.cluster.shutdown() self.session.shutdown() log.info('Connection closed.')

Cassandra client

def prepareStatement(self): self.insert_page_statement = self.session.prepare(""" INSERT INTO wikipedia.pages (url, title, abstract, length, refs) VALUES (?, ?, ?, ?, ?); """)

def insertPage(self, url, title, abstract, length, refs): self.session.execute( self.insert_page_statement.bind( (url, title, abstract, length, refs)))

Cassandra client

$HADOOP_HOME/bin/hadoop jar $HADOOP_HOME/share/hadoop/tools/lib/hadoop-streaming-2.4.0.jar \ -files mapper.py,reducer.py \ -mapper ./mapper.py \ -reducer ./reducer.py \ -jobconf stream.num.map.output.key.fields=1 \ -jobconf stream.num.reduce.output.key.fields=1 \ -jobconf mapred.reduce.tasks=16 \ -input wikipedia-latest-abstract \ -output $HADOOP_OUTPUT_DIR

YARN: mapreduce v2

Using map-reduce and yarn

wikipedia abstracts(url, title, abstract, sections)

hadoopmapper.sh

hadoopreducer.sh

Publish pages on Cassandra

Extract inverted index

Top 10 Urls per word go to Cassandra

Inverted index : Apple -> Apple Inc, Apple Tree, The Big Apple

Export inverted inded

during "reduce" phase

SELECT TRANSFORM (url, abstract, links) USING 'mapper.py' AS (relevance, url)FROM hive_wiki_tableORDER BY relevance LIMIT 50;

Hive UDF

functions and

hooks

Second method: using hive sql queriesdef emit_ranking(n=100): global sorted_dict for i in range(n): cassandra_client.insertWord(current_word, relevance, url)

…

def readLoop(): # input comes from STDIN for line in sys.stdin: # parse the input we got from mapper.py word, relevance, url = line.split('\t', 2)

if current_word == word : sorted_dict[relevance] = url else: if current_word: emit_ranking()… Reducer ...

memory

disk compute disk

diskcomputedisk

memory

disk diskcompute

memory

disk diskcompute

memory

memory

diskcomputedisk

map (k,v) shuffle & sort reduce (k,list(v))

compute

cassandra

cassandra

Front-end:

@app.route('/word/<keyword>')def fetch_word(keyword): db = get_cassandra() pages = [] results = db.fetchWordResults(keyword) for hit in results: pages.append(db.fetchPageDetails(hit["url"]))

return Response(json.dumps(pages), status=200, mimetype="application/json")

if __name__ == '__main__': app.run()

Front-End:

prototyping in Flask

Expose during Map or Reduce?

Expose Map

- only access to local information

- simple, distributed "awk" filter

Expose in Reduce

- need to collect data scattered across your cluster

- analysis on all the available data

Latency tradeoffs

Two runtimes frameworks: cassandra : in-memory, low-latencyhadoop : extensive, exhaustive, churns all the data

Statistics and machine learning:

Python and R : they can be used for batch and/or realtime

Fastest analysis: still the domain on C, Java, Scala

Some lessons learned

● Use mapreduce to (pre)process data● Connect to Cassandra during MR ● Use MR as for batch heavy lifting

● Lambda architecture: Fast Data + All Data

Some lessons learned

Expose results to Cassandra for fast access

- responsive apps

- high troughput / low latency

Hadoop as a background tool

- data validation, new extractions, new algorithms

- data harmonization, correction, immutable system of records

The tutorial is on github

https://github.com/natalinobusa/wikipedia

Parallelism Mathematics Programming

Languages Machine Learning Statistics

Big Data Algorithms Cloud Computing

Natalino Busa@natalinobusa

www.natalinobusa.com

Thanks !Any questions?