NewSQL Database

민형기

hg.min@samsung.com

2014. 2. 5.

[SSA] Big Data Analytics

1

I. Why NewSQL?

II. NewSQL 기본 개념

III. NewSQL 종류

IV.NewSQL 정리

Contents

2

Why NewSQL?

3

Thinking – Extreme Data

Qcon London 2012

4 출처 : Netflix in the Cloud (http://www.slideshare.net/adrianco/netflix-in-the-cloud-2011)

Thinking - Traffic Explosion

5 Qcon London 2012

Organizations need deeper insights

6

Solutions

□Buy High end Technology

□Higher more developers

□Using NoSQL

□Using NewSQL

7

Solution – Buy High End Technology

Oracle, IBM

8

Solution – Higher more developers

http://www.trekbikes.com/us/en/bikes/road/race_performance/madone_4_series/madone_4_5

□Application Level Sharding

□Build your replication middleware

□…

9

Solutions – Use NoSQL

□새로운 비 관계형 데이터 베이스

□분산 아키텍처

□수평 확장성

□고정된 테이블 스키마가 없음

□Join, UPDATE, DELETE 연산이 없음

□트랜잭션이 없음

□SQL 지원이 없음

10

NoSQL Ecosystems

451 group

11

MongoDB

□Document-oriented database JSON-style documents: Lists, Maps, primitives

Schema-less

□Transaction = update of a single document

□Rich query language for dynamic queries

□Tunable writes: speed reliability

□Highly scalable and available

12

MongoDB 사용예

□Use cases High volume writes

Complex data

Semi-structured data

□주요 고객 Foursquare

Bit.ly Intuit

SourceForge, NY Times

GILT Groupe, Evite,

SugarCRM

13

Apache Cassandra

□Column-oriented database/Extensible row store Think Row ~= java.util.SortedMap

□Transaction = update of a row

□Fast writes = append to a log

□Tunable reads/writes: consistency / availability

□Extremely scalable

Transparent and dynamic clustering

Rack and datacenter aware data replication

□CQL = “SQL”-like DDL and DML

14

Apache Cassandra 사용 예

□사용 예 Big data

Multiple Data Center distributed database

Persistent cache

(Write intensive) Logging

High-availability (writes)

□주요 고객 Digg, Facebook, Twitter, Reddit, Rackspace

Cloudkick, Cisco, SimpleGeo, Ooyala, OpenX

The largest production cluster has over 100 TB of data in over 150 machines.“ – Casssandra web site

15

□새로운 관계형 데이터베이스

□SQL과 ACID 트랜잭션을 유지

□새롭고 개선된 분산 아키텍처

□뛰어난 확장성과 성능을 지원

□NewSQL vendors: TokuDB, ScaleDB, NimbusDB, ..., VoltDB

Solutions – Use NewSQL

16 http://www.cs.brown.edu/courses/cs227/slides/newsql/newsql-intro.pdf

17

NewSQL 정의 – Wikipedia

NewSQL is a class of modern relational

database management systems that seek to

provide the same scalable performance of

NoSQL systems for OLTP workloads while still

maintaining the ACID guarantees of a

traditional single-node database system

NewSQL is a class of modern relational

database management systems that seek to

provide the same scalable performance of

NoSQL systems for OLTP workloads while still

maintaining the ACID guarantees of a

traditional single-node database system

http://en.wikipedia.org/wiki/NewSQL

18

NewSQL 정의 – 451 Group

A DBMS that delivers the scalability and

flexibility promised by NoSQL while retaining

the support for SQL queries and/or ACID, or

to improve performance for appropriate

workloads.

A DBMS that delivers the scalability and

flexibility promised by NoSQL while retaining

the support for SQL queries and/or ACID, or

to improve performance for appropriate

workloads.

http://www.cs.brown.edu/courses/cs227/slides/newsql/newsql-intro.pdf

19

NewSQL 정의 – Stonbraker

SQL as the primary interface.

ACID support for transactions

Non-locking concurrency control.

High per-node performance.

Parallel, shared-nothing architecture.

SQL as the primary interface.

ACID support for transactions

Non-locking concurrency control.

High per-node performance.

Parallel, shared-nothing architecture.

http://www.cs.brown.edu/courses/cs227/slides/newsql/newsql-intro.pdf

20

NewSQL Category New Database New MySQL Storage Engines Transparent Clustering

21 OSBC

The evolving database landscape

22

MySQL Ecosystem

23

NewSQL Ecosystem

24

New Database

□ Newly designed from scratch to achieve scalability and performance One of the key considerations in improving the performance is

making non-disk (memory) or new kinds of disks (flash/SSD) the primary data store.

some (hopefully minor) changes to the code will be required and data migration is still needed.

□Solutions Software-Only: VoltDB, NuoDB, Drizzle, Google Spanner

Supported as an appliance: Clustrix, Translattice.

http://www.linuxforu.com/2012/01/newsql-handle-big-data/

25

New MySQL Storage Engines

□Highly optimized storage engines for MySQL

□Scale better than built-in engines, such as InnoDB. Good part: the usage of the MySQL interface

Downside part: data migration from other databases

□Solutions TokuDB, MemSQL, Xeround, Akiban, NDB

http://www.linuxforu.com/2012/01/newsql-handle-big-data/

26

Transparent Clustering

□Retain the OLTP databases in their original format, but provide a pluggable feature Cluster transparently

Ensure Scalability

□Avoid the rewrite code or perform any data migration

□Solutions Cluster transparently: Schooner MySQL, Continuent

Tungsten, ScalArc

Ensure Scalability: ScaleBase, dbShards

http://www.linuxforu.com/2012/01/newsql-handle-big-data/

27

NewSQL Products VoltDB Google Spanner MySQL Cluster Architecture

28

29

VoltDB

http://voltdb.com/products-services/products, http://www.slideshare.net/chris.e.richardson/polygot-persistenceforjavadevs-jfokus2012reorgpptx

□VoltDB, 2010, AGPLv3/VoltDB Proprietary License, Java/C++ □Type: NewSQL, New Database □Main Point: In-memory Database, Java Stored Procedure, VoltDB

implements the design of the academic H-Store project □Protocol: SQL □Transaction: Yes □Data Storage: Memory

□Features

□ in-memory relational database □Durability thru replication, snapshots, logging □Transparent partitioning □ACID-level consistency □Synchronous multi-master replication □Database Replication

30

VoltDB- Technical Overview

“OLTP Through the Looking Glass”

VoltDB는 전통 DB의 오버헤드 회피함 – 데이터 및 관련 프로세싱은 함께 분할 되고, CPU 코어

단위로 분산됨

Shared-Nothing Architecture Horizontally Scale

– 데이터는 메인 메모리에서 유지됨

버퍼관리가 필요 없음

– Transaction은 메모리에서 순차적으로 실행됨

no locking & latching

– Synchronous multi-master replication: HA

– Command Logging: “write-ahead” 데이터 로깅을 대체하여 고성능을 제공

출처: http://odbms.org/download/VoltDBTechnicalOverview.pdf, http://cs-www.cs.yale.edu/homes/dna/papers/oltpperf-sigmod08.pdf

31

X X

X

X X

VoltDB - Partitions (1/3)

1 partition per physical CPU core –Each physical server has multiple VoltDB partitions

Data - Two types of tables –Partitioned

Single column serves as partitioning key Rows are spread across all VoltDB partitions by partition column Transactional data (high frequency of modification)

–Replicated All rows exist within all VoltDB partitions Relatively static data (low frequency of

modification)

Code - Two types of work – both ACID –Single-Partition

All insert/update/delete operations within single partition Majority of transactional workload

–Multi-Partition CRUD against partitioned tables across multiple partitions Insert/update/delete on replicated tables

출처: http://strataconf.com/stratany2013/public/schedule/detail/31731

32

VoltDB - Partitions (2/3)

Single-partition vs. Multi-partition

1 101 2

1 101 3

4 401 2

1 knife

2 spoon

3 fork

Partition 1

2 201 1

5 501 3

5 502 2

1 knife

2 spoon

3 fork

Partition 2

3 201 1

6 601 1

6 601 2

1 knife

2 spoon

3 fork

Partition 3

table orders : customer_id (partition key) (partitioned) order_id product_id

table products : product_id (replicated) product_name

select count(*) from orders where customer_id = 5 single-partition

select count(*) from orders where product_id = 3 multi-partition

insert into orders (customer_id, order_id, product_id) values (3,303,2) single-partition

update products set product_name = ‘spork’ where product_id = 3 multi-partition

33

VoltDB - Partitions (3/3)

Looking inside a VoltDB partition… – Each partition contains data and an

execution engine.

– The execution engine contains a queue for transaction requests.

– Requests are executed sequentially (single threaded).

Work

Queue

execution engine

Table Data Index Data

- Complete copy of all replicated tables - Portion of rows (about 1/partitions) of all partitioned tables

34

VoltDB - Compiling

The database is constructed from – The schema (DDL)

– The work load (Java stored procedures)

– The Project (users, groups, partitioning)

VoltCompiler creates application catalog – Copy to servers along with 1 .jar and

1 .so

– Start servers

CREATE TABLE HELLOWORLD (

HELLO CHAR(15),

WORLD CHAR(15),

DIALECT CHAR(15),

PRIMARY KEY (DIALECT)

);

Schema

import org.voltdb. * ;

@ProcInfo(

partitionInfo = "HELLOWORLD.DIA

singlePartition = true

)

public class Insert extends VoltPr

public final SQLStmt sql =

new SQLStmt("INSERT INTO HELLO

public VoltTable[] run( String hel

import org.voltdb. * ;

@ProcInfo(

partitionInfo = "HELLOWORLD.DIA

singlePartition = true

)

public class Insert extends VoltPr

public final SQLStmt sql =

new SQLStmt("INSERT INTO HELLO

public VoltTable[] run( String hel

import org.voltdb. * ;

@ProcInfo(

partitionInfo = "HE

singlePartition = t

public final SQLStmt

public VoltTable[] run

Stored Procedures

<?xml version="1.0"?>

<project>

<database name='data

<schema path='ddl.

<partition table=‘

</database>

</project>

Project.xml

35

VoltDB - Transactions

All access to VoltDB is via Java stored procedures (Java + SQL)

A single invocation of a stored procedure is a transaction (committed on success)

Limits round trips between DBMS and application

High performance client applications communicate synchronously with VoltDB

SQL

36

VoltDB - Clusters/Durability

Scalability – Increase RAM in servers to add capacity

– Add servers to increase performance / capacity

– Consistently measuring 90% of single-node performance increase per additional node

High availability – K-safety for redundancy

Snapshots – Scheduled, continuous, on demand

Spooling to data warehouse

Disaster Recovery/WAN replication (Future) – Asynchronous replication

37

Google Spanner

38 출처: http://research.google.com/archive/spanner.html

Google Spanner Overview

구글의 확장성, 다중버전, 전 세계적으로 분산, 동기적으로 복제된 데이터베이스

Google, 2012, Paper, C++

Type: NewSQL, New Database

Main Point: Distributed multiversion database

특징

– General-purpose transactions (ACID)

– SQL query language

– Schematized tables

– Semi-relational data model

Running in production

– Storage for Google’s ad data(F1)

– Replaced a sharded MySQL database

39

Google Spanner - Key Features

Temporal Multi-version database

Externally consistent global write-transactions with synchronous replication.

Transactions across Datacenters.

Lock-free read-only transactions.

Schematized, semi-relational (tabular) data model.

SQL-like query interface.

Auto-sharding, auto-rebalancing, automatic failure response.

Exposes control of data replication and placement to user/application.

Enables transaction serialization via global timestamps

Acknowledges clock uncertainty and guarantees a bound on it

Uses novel TrueTime API to accomplish concurrency control

Uses GPS devices and Atomic clocks to get accurate time

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

40 출처: http://www.cs.cornell.edu/projects/ladis2009/talks/dean-keynote-ladis2009.pdf

Google Spanner - Design Goals

41

Google Spanner - Architecture

• Universe: Spanner 전체 집합 • Zone: 물리적으로 독립되어 운영할 수 있는 단위 • 1대의 존마스터(zonemaster)+ 수백~수천 대의 스팬서버(spanserver)로 구성됨 • 존마스터는 스팬서버에 데이터를 할당, 스팬서버는 실제 데이터를 저장하고 처리 • 로케이션 프록시: 클라이언트에 의해 호출되어, 접근해야 할 데이터가 어느 스팬서버에 있는지 알려줌

출처: http://helloworld.naver.com/helloworld/216593

42

Google Spanner - Software Stack (1/3)

• 스팬서버는 100~1000개의 태블릿(tablet)을 관리. • 태블릿: ‘(key:string, timestamp:int64) string’ 형태의 매핑을 다수개 저장, 멀티다중 버전 데이터베이스 특성 • 태블릿의 상태는 B-트리 파일과 WAL로 CFS에 저장됨 • 스팬서버간 데이터 복제를 지원하기 위해 팍소스 스테이트 머신을 이용

출처: http://helloworld.naver.com/helloworld/216593

43

Google Spanner - Software Stack (2/3)

(key:string, timestamp:int64) → string

Back End: Colossus (successor to GFS)

Paxos State Machine on top of each tablet stores meta data and logs of the tablet.

Leader among replicas in a Paxos group is chosen and all write requests for replicas in that group initiate at leader.

Transaction Leader

– Is Paxos Leader if transaction involves one Paxos group

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

44

Google Spanner - Software Stack (3/3)

Directory – 같은 접두어를 사용하는 연속된 키 모음

– 빅테이블(BigTable)의 버킷과 유사

– 데이터 배치의 최소 단위

– 지리적인 리플리카 배치의 최소단위

디렉터리의 크기가 너무 커질 경우, 하나의 디렉터리를 여러 개의 프래그먼트(fragment)로 분할 가능

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

45

Google Spanner - Data Model

One or more databases supported in Spanner Universe

Database can contain unlimited schematized tables

Not purely relational

– Requires rows to have names

– Names are nothing but a set(can be singleton) of primary keys

– In a way, it’s a key value store with primary keys mapped to non-key columns as values

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

46

Google Spanner - TrueTime

“Global wall-clock time” with bounded uncertainty

Novel API behind Spanner’s core innovation

Leverages hardware features like GPS and Atomic Clocks

Implemented via TrueTime API.

–Key method being now() which not only returns current system time but also another value (ε) which tells the maximum uncertainty in the time returned

Set of time master server per datacenters and time slave daemon per machines.

Majority of time masters are GPS fitted and few others are atomic clock fitted (Armageddon masters).

Daemon polls variety of masters and reaches a consensus about correct timestamp.

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

47

Google Spanner - True Time

time

earliest latest

TT.now()

2*ε

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

48

Google Spanner - TrueTime Transaction

Read-Write – requires lock.

Read-Only – lock free.

–Requires declaration before start of transaction.

–Reads information that is up to date

Snapshot Read – Read information from past by specifying a timestamp or bound

–Use specifies specific timestamp from past or timestamp bound so that data till that point will be read.

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

49

Google Spanner - Evaluation(1/2)

Evaluated for replication, transactions and availability.

Results on epsilon of TrueTime

Benchmarked on Spanner System with

–50 Paxos groups

–250 Directories

–Clients(applicatons) and Zones are at a network distance of 1ms

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

50

Google Spanner - Evaluation (2/2)

Effect of killing servers on throughput Distribution of TrueTime Epsilon values

출처: http://www.cse.buffalo.edu/~okennedy/courses/cse704fa2012/9.2-Spanner.ppt

51

MySQL Cluster Architecture

http://dev.mysql.com/doc/refman/5.5/en/mysql-cluster-overview.html

52

Schooner MySQL Active Cluster

http://www.snia.org/sites/default/files2/SDC2011/presentations/monday/DrJohnBuschHow_ScaleUp_Scale_Out.pdf

53

dbShards Architecture

http://www.linuxforu.com/2012/01/newsql-handle-big-data/

54

NewSQL 정리

55

Database 업계의 3가지 Trends

□NoSQL 데이터베이스:

분산 아키텍처의 확장성 등의 요구 사항을 충족하며, 스키마 없는 데이터

관리 요구 사항에 부합하도록 설계됨.

□NewSQL 데이터베이스:

분산 아키텍처의 확장성 등의 요구 사항을 충족하거나 혹은 수평 확장을

필요로하지 않지만 성능을 개선은 되도록 설계됨.

□Data Grid/Cache 제품:

응용 프로그램 및 데이터베이스 성능을 높이기 위해 메모리에 데이터를

저장하도록 설계됨.

56

결론 □데이터 저장을 위한 많은 솔루션이 존재

□ Oracle, MySQL만 있다는 생각은 버려야 함 □ 먼저 시스템의 데이터 속성과 요구사항을 파악(CAP, ACID/BASE) □ 한 시스템에 여러 솔루션을 적용

소규모/복잡한 관계 데이터: RDBMS 대규모 실시간 처리 데이터: NoSQL, NewSQL 대규모 저장용 데이터: Hadoop 등

□적절한 솔루션 선택 □ 반드시 운영 중 발생할 수 있는 이슈에 대해 검증 후 도입 필요 □ 대부분의 NewSQL 솔루션은 베타 상태(섣부른 선택은 독이 될 수 있음) □ 솔루션의 프로그램 코드 수준으로 검증 필요

□NewSQL 솔루션에 대한 안정성 확보 □ 솔루션 자체의 안정성은 검증이 필요하며 현재의 DBMS 수준의 안정성은 지원하

지 않음 □ 반드시 안정적인 데이터 저장 방안 확보 후 적용 필요 □ 운영 및 개발 경험을 가진 개발자 확보 어려움 □ 요구사항에 부합되는 NewSQL 선정 필요

□처음부터 중요 시스템에 적용하기 보다는 시범 적용 필요 □ 선정된 솔루션 검증, 기술력 내재화

57

감사합니다.

58

Appendix.

59

Early – 2000s

http://www.cs.brown.edu/courses/cs227/slides/newsql/newsql-intro.pdf

□All the big players were heavyweight and expensive.

Oracle, DB2, Sybase, SQL Server, etc.

□Open-source databases were missing important features.

Postgres, mSQL, and MySQL.

60

Early – 2000s : eBay Architecture

http://highscalability.com/ebay-architecture

61

Early – 2000s : eBay Architecture

http://highscalability.com/ebay-architecture

Push functionality to application: Joins Referential integrity Sorting done

No distributed transactions

62

Mid– 2000s

http://www.cs.brown.edu/courses/cs227/slides/newsql/newsql-intro.pdf

□MySQL + InnoDB is widely adopted by new web companies:

Supported transactions, replication, recovery.

Still must use custom middleware to scale out across multiple machines.

Memcache for caching queries.

63

Mid – 2000s : Facebook Architecture

http://www.techthebest.com/2011/11/29/technology-used-in-facebook/

64

Mid – 2000s : Facebook Architecture

http://www.techthebest.com/2011/11/29/technology-used-in-facebook/

Scale out using custom middleware. Store ~75% of database in Memcache. No distributed transactions.

65

Late – 2000s

http://www.cs.brown.edu/courses/cs227/slides/newsql/newsql-intro.pdf

□MySQL + InnoDB is widely adopted by new web companies:

Supported transactions, replication, recovery.

Still must use custom middleware to scale out across multiple machines.

Memcache for caching queries.

66

Late – 2000s : MongoDB Architecture

http://sett.ociweb.com/sett/settAug2011.html

67

Late – 2000s : MongoDB Architecture

http://sett.ociweb.com/sett/settAug2011.html

Easy to use. Becoming more like a DBMS over time. No transactions.

68

Early – 2010s

http://www.cs.brown.edu/courses/cs227/slides/newsql/newsql-intro.pdf

□New DBMSs that can scale across multiple machines natively and provide ACID guarantees.

MySQL Middleware

Brand New Architectures

69

Database SPRAIN (by 451Group)

70

Database SPRAIN

□“An injury to ligaments... caused by being stretched beyond normal capacity”

□Six key drivers for NoSQL/NewSQL/DDG adoption Scalability

Performance

Relaxed consistency

Agility

Intricacy

Necessity

71

Database SPRAIN - Scalability

□Associated sub-driver: Hardware economics Scale-out across clusters of commodity servers

□Example project/service/vendor BigTable HBase Riak MongoDB Couchbase, Hadoop

Amazon RDS, Xeround, SQL Azure, NimbusDB

Data grid/cache

□Associated use case: Large-scale distributed data storage

Analysis of continuously updated data

Multi-tenant PaaS data layer

72

Database SPRAIN - Scalability

□User: StumbleUpon

□Problem: Scaling problems with recommendation engine on MySQL

□Solution: HBase Started using Apache HBase to provide real-time analytics on Su.pr

MySQL lacked the performance headroom and scale

Multiple benefits including avoiding declaring schema

Enables the data to be used for multiple applications and use cases

73

Database SPRAIN - Performance

□Associated sub-driver: MySQL limitations Inability to perform consistently at scale

□Example project/service/vendor Hypertable Couchbase Membrain MongoDB Redis

Data grid/cache

VoltDB, Clustrix

□Associated use case: Real time data processing of mixed read/write workloads

Data caching

Large-scale data ingestion

74

Database SPRAIN - Performance

□User: AOL Advertising

□Problem: Real-time data processing to support targeted advertising

□Solution: Membase Server Segmentation analysis runs in CDH, results passed into Membase

Make use of its sub-millisecond data delivery

More time for analysis as part of a 40ms targeted and response time

Also real time log and event management

75

Database SPRAIN – Relaxed Consistency

□Associated sub-driver: CAP theorem The need to relax consistency in order to maintain availability

□Example project/service/vendor: Dynamo, Voldemort, Cassandra

Amazon SimpleDB

□Associated use case: Multi-data center replication

Service availability

Non-transactional data off-load

76

Database SPRAIN – Relaxed Consistency

□User: Wordnik

□Problem: MySQL too consistent –blocked access to data during inserts and

created numerous temp files to stay consistent.

□Solution: MongoDB Single word definition contains multiple data items from various

sources

MongoDB stores data as a complete document

Reduced the complexity of data storage

77

Database SPRAIN – Agility

□ Associated sub-driver: Polyglot persistence Choose most appropriate storage technology for app in development

□Example project/service/vendor MongoDB, CouchDB, Cassandra

Google App Engine, SimpleDB, SQL Azure

□Associated use case: Mobile/remote device synchronization

Agile development

Data caching

78

Database SPRAIN – Agility

□ User: Dimagi BHOMA (Better Health Outcomes through Mentoring and Assessments) project

□Problem: Deliver patient information to clinics despite a lack of reliable Internet

connections

□Solution: Apache CouchDB Replicates data from regional to national database

When Internet connection, and power, is available

Upload patient data from cell phones to local clinic

79

Database SPRAIN – Intricacy

□ Associated sub-driver: Big data, total data Rising data volume, variety and velocity

□Example project/service/vendor Neo4j GraphDB, InfiniteGraph

Apache Cassandra, Hadoop,

VoltDB, Clustrix

□Associated use case: Social networking applications

Geo-locational applications

Configuration management database

80

Database SPRAIN – Intricacy

□User: Evident Software

□Problem: Mapping infrastructure dependencies for application performance

management

□Solution: Neo4j Apache Cassandra stores performance data

Neo4j used to map the correlations between different elements

Enables users to follow relationships between resources while investigating issues

81

Database SPRAIN – Necessity

□ Associated sub-driver: Open source The failure of existing suppliers to address the performance,

scalability and flexibility requirements of large-scale data processing

□ Example project/service/vendor BigTable, Dynamo, MapReduce, Memcached

Hadoop HBase, Hypertable, Cassandra, Membase

Voldemort, Riak, BigCouch

MongoDB, Redis, CouchDB, Neo4J

□Associated use case: All of the above

82

Database SPRAIN – Necessity

□BigTable: Google

□Dynamo: Amazon

□Cassandra: Facebook

□HBase: Powerset

□Voldemort: LinkedIn

□Hypertable: Zvents

□Neo4j: Windh Technologies

Yahoo: Apache Hadoop and Apache HBase

Digg: Apache Cassandra

Twitter: Apache Cassandra, Apache Hadoop and FlockDB