Cassandra FrOSCon 10

Jonathan [email protected] / @spyced

Inside the Cassandra Database

Saturday, August 21, 2010

mailto:[email protected]

mailto:[email protected]

Why NoSQL?

✤ Relational databases don’t scale

✤ The relational model maps poorly to some problems

✤ Relational databases are slow


Myth 1

✤ “NoSQL is for people who don’t understand {SQL, denormalization, query tuning, ...}”

✤ Similarly: “Only users of [database X] are turning to NoSQL databases, because X sucks.”


eBay: NoSQL pioneer

✤ “BASE is diametrically opposed to ACID. Where ACID is pessimistic and forces consistency at the end of every operation, BASE is optimistic and accepts that the database consistency will be in a state of flux. Although this sounds impossible to cope with, in reality it is quite manageable and leads to levels of scalability that cannot be obtained with ACID.”

✤ --BASE: An Acid Alternative, Dan Pritchett, eBay

✤ See also: The eBay Architecture, Randy Shoup and Dan Pritchett


(“The eBay Architecture,” Randy Shoup and Dan Pritchett)


Myth 2

✤ “NoSQL is nothing new because we had key/value databases like bdb years ago.”


Myth 3

✤ “Only huge web 2.0 sites like Facebook and Twitter care about scalability.”


Cassandra





Use cases

✤ Digital Reasoning: NLP + entity analytics

✤ OpenX: largest publisher-side ad network in the world

✤ Cloudkick: performance data & aggregation

✤ SimpleGEO: location-as-API

✤ Ooyala: video analytics and business intelligence

✤ ngmoco: massively multiplayer game worlds


Cassandra





Cassandra memory-aware index

<row data 0><row data 1>

...<row data 127>

...<row data 255>

...

<key 127><key 255>

...


Commitlog

MemtableWriterReader

The Log-Structured Merge-Tree,Bigtable: A Distributed Storage System for Structured Data


Durable

✤ Write to commitlog

✤ fsync is cheap since it’s append-only

✤ Write to memtable

✤ [amortized] flush memtable to sstable


Scaling


A

L

T

W


A

L

T

W

F


A

L

T

W

F(A-L]


A

L

T

W

F(A-F]

(F-L]


A

L

T

W

F

Key “C”


Reliability

✤ No single points of failure, clean design

✤ Multiple datacenters

✤ Monitorable


Some headlines

✤ “Resyncing Broken MySQL Replication”

✤ “How To Repair MySQL Replication”

✤ “Fixing Broken MySQL Database Replication”

✤ “Replication on Linux broken after db restore”

✤ “MySQL :: Repairing broken replication”


http://homepage.mac.com/kelleherk/iblog/C711669388/E226281480/index.html

http://homepage.mac.com/kelleherk/iblog/C711669388/E226281480/index.html

http://www.howtoforge.com/how-to-repair-mysql-replication

http://www.howtoforge.com/how-to-repair-mysql-replication

http://mike.kruckenberg.com/archives/2007/12/fixing-broken-mysql-database-replication.html

http://mike.kruckenberg.com/archives/2007/12/fixing-broken-mysql-database-replication.html

http://forums.mysql.com/read.php?26,180839

http://forums.mysql.com/read.php?26,180839

The opposite of heroes

✤ “If your software wakes someone up at 4 AM to fix it, you’re doing it wrong.”


Good architecture solves multiple problems at once

✤ Availability in single datacenter

✤ Availablility in multiple datacenters

✤ Built-in repair rather than an afterthought

✤ or worse, having to restart replication entirely


A

LT

W

F

P

YKey “C”

U


A

LT

W

P

Y

UF


A

LT

W

F

P

Y

U


A

LT

W

F

P

YKey “C”

U


A

LT

W

F

P

YKey “C”

U

XSaturday, August 21, 2010

A

LT

W

F

P

YKey “C”

U

Xhint


A

LT

W

F

P

Y

U


Eventual Tuneable consistency

✤ ONE, QUORUM, ALL

✤ R + W > N

✤ Choose availability vs consistency (and latency)


Monitorable


Events


0

375

750

1125

1500

Jan(0.5)

Feb(0.5.1) Mar

Apr(0.6, 0.6.1)

May(0.6.2)

Jun(0.6.3)

Jul(0.6.4)

mails sent


Data model

✤ Twitter: “Fifteen months ago, it took two weeks to perform ALTER TABLE on the statuses [tweets] table.”


Columns

ColumnFamilies


SELECT * FROM tweetsWHERE user_id IN (SELECT follower FROM followers WHERE user_id = ?)ORDER BY time_tweeted DESCLIMIT 40

followers

?

tweets

timeline

?

uuid:tweet

Cassandra “indexes” are materialized views

SORT


Analytics in Cassandra

✤ @afex: “Cassandra + Pig (Hadoop) is very exciting. A 7 line script to analyze data from my entire cluster transparently, with no ETL? Yes, please”


TaskTracker

JobTracker


Coming in 0.7 [beta1 released 13/8]

✤ Secondary indexes and expressions

✤ Large (> 2GB) rows

✤ More control over replica placement

✤ Online schema changes

✤ Flow control

✤ Dynamic routing around slow nodes


More

✤ http://wiki.apache.org/cassandra/ArticlesAndPresentations

✤ http://wiki.apache.org/cassandra/ArchitectureInternals


http://wiki.apache.org/cassandra/ArticlesAndPresentations




http://wiki.apache.org/cassandra/ArchitectureInternals

http://wiki.apache.org/cassandra/ArchitectureInternals

Questions


Cassandra FrOSCon 10

Technology

Transcript of Cassandra FrOSCon 10