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Cassandra presentation given at the 3rd annual Palmetto Open Source Software Conference (POSSCON 2010).
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Outside The Box With Apache Cassandra
Eric [email protected]
@jericevans
Palemetto Open Source Software ConferenceApril 16, 2010
Cassandra is...
A massively scalable, decentralized, structured data store (akadatabase).
Outline
1 Background
2 Project History
3 Description
4 Case Studies
5 Roadmap
The Digital Universe
Consolidation
Old Guard
Vertical Scaling Sucks
CAP Theorem (aka Brewer’s Theorem)
Distributed systems cannot provide all three of:
• Consistency
• Availability
• Partition Tolerance
Influential Papers
Dynamo: Amazon’s Highly Available Key-value Store 1
• Voldemort
• Riak
Bigtable: A Distributed Storage System for Structured Data 2
• Hypertable
• HBase
1http:
//www.allthingsdistributed.com/2007/10/amazons_dynamo.html2http://labs.google.com/papers/bigtable-osdi06.pdf
Outline
1 Background
2 Project History
3 Description
4 Case Studies
5 Roadmap
• 7 new committers added
• Dozens of contributors
• 200+ (!) people on IRC
• Hundreds of closed issues (bugs, features, etc)
• 4 major releases; a number of stable point releases
• Graduation to TLP
Outline
1 Background
2 Project History
3 Description
4 Case Studies
5 Roadmap
Cassandra is...
• O(1) DHT
• Eventual consistency
• Tunable trade-offs, consistency vs. availability
But...
• Values are structured, indexed
• Columns / column families
• Slicing w/ predicates (queries)
Column families
Supercolumn families
Client API
• Thrift (12 different languages!)3
• High-level client libraries• Ruby• Perl• Python (Twisted too)• Scala• Java• PHP• Grails• C++
3http://incubator.apache.org/thrift
Querying
• get(): retrieve by column name
• multiget(): by column name for a set of keys
• get slice(): by column name, or a range of names• returning columns• returning super columns
• multiget slice(): a subset of columns for a set of keys
• get count: number of columns or sub-columns
• get range slice(): subset of columns for a range of keys
Updating
• insert(): add/update column (by key)
• batch insert(): add/update multiple columns (by key)
• remove(): remove a column
• batch mutate(): like batch insert() but can also delete(new for 0.6, deprecates batch insert())
Column comparators
• TimeUUID
• LexicalUUID
• UTF8
• Long
• Bytes
• ...
Consistency
CAP Theorem: choose any two of Consistency, Availability, orPartition tolerance.
• Zero
• One
• Quorum ((N / 2) + 1)
• All
About writes...
• Atomic within a column family
• Any node
• Always writeable (hinted hand-off)
• Fast
Writes
About reads...
• Any node
• Read repair
• Key cache
• Record cache
Reads
Outline
1 Background
2 Project History
3 Description
4 Case Studies
5 Roadmap
Case 1: Digg
Digg is a social news site that allows people to discover and sharecontent from anywhere on the Internet by submitting stories andlinks, and voting and commenting on submitted stories and links.
Ranked 98th by Alexa.com.
Digg
Problem
• Terabytes of data; high transaction rate (reads dominated)
• Multiple clusters; heavily sharded
• Management nightmare (high effort, error prone)
• Unsatisfied availability requirements (geographic isolation)
Solution
• Currently production on ”Green Badges”
• Cassandra as primary data store RSN
• Datacenter and rack-aware replication
Case 2: Twitter
Twitter is a social networking and microblogging service thatenables its users to send and read tweets, text-based posts of up to140 characters.
Ranked 12th by Alexa.com.
MySQL
• Terabytes of data, ˜1,000,000 ops/s
• Calls for heavy sharding, light replication
• Schema changes are very difficult, (if possible at all)
• Manual sharding is very high effort
• Automated sharding and replication is Hard
Case 3: Facebook
Facebook is a social networking site where users can create aprofile, add friends, and send them messages. Users can also joingroups organized by location or other points of common interest.
Ranked #2 by Alexa.com.
Inbox Search
• 100 TB
• 160 nodes
• 1/2 billion writes per day (2yr old number?)
Outline
1 Background
2 Project History
3 Description
4 Case Studies
5 Roadmap
0.6
• batch mutate command
• authentication (basic)
• new consistency level, ANY
• fat client
• mmapped i/o reads (default on 64bit jvm)
• improved write concurrency (HH)
• networking optimizations
• row caching
• improved management tools
• per-keyspace replication factor
0.7
• more efficient compactions (row sizes bigger than memory)
• easier (dynamic?) column family changes
• SSTable versioning
• SSTable compression
• support for column family truncation
• improved configuration handling
• remove key range command
• even more improved management tools
• vector clocks w/ server-side conflict resolution
Questions?