Cassandra London UG July 2011 - Riak vs Cassandra

Transcript

1. Riak
   How does Riak compare to Cassandra?
   Friday, 20 April 12
   

   View Slide

2. /usr/bin/whoami
   • Russell Smith
   • Work for UKD1, a consultancy for web-related-tech
   • Help with application design, infrastructure, capacity planning, etc
   • Mainly for the video-games industry & web-startups
   • Twitter: @ukd1
   Friday, 20 April 12
   

   View Slide

3. What is Riak?
   • Pronounced ‘ree-ack’
   • A scalable, high-availability, distributed, key-value store
   • Modelled on Amazon’s description of Dynamo, like Cassandra
   • Commercially supported / developed by Basho
   • Written in Erlang
   • Open source - Apache License (2.0)
   Friday, 20 April 12
   

   View Slide

4. What isn’t Riak?
   • Schema enforced - store what you want
   • Relational database - No joins or constraint enforcement as there are no global locks
   • Not intended to compete with in-memory column based databases
   Friday, 20 April 12
   

   View Slide

5. What versions are available?
   • Riak
   • Riak Search (Riak + distributed full-text indexing / search)
   • Riak Enterprise - commercially licensed - supports extra features for
   enterprise use (SNMP, data-centre awareness, etc)
   • Luwak (Riak + app for storing large files; it’s bundled by default)
   Friday, 20 April 12
   

   View Slide

6. Riak’s take on CAP
   • Exposed to the end user - allowing tuning of N, R & W
   • N - # of nodes, set per bucket (default of 3)
   • R - # of nodes required for a read (per request)
   • W - # of nodes required for a successful write (a number, all, quorum
   or default for the bucket)
   Friday, 20 April 12
   

   View Slide

7. Client libraries
   • PHP, Python, Ruby, Java, Erlang, Javascript, .NET
   • Community client libraries;
   • C, Clojure, Go, Griffon, Groovy, Haskell, Perl, Scala, Smalltalk
   Friday, 20 April 12
   

   View Slide

8. What can you store?
   • Values against keys
   • Keys are organised in to buckets
   • Practical value limit of 64mb
   • For large files; Luwak (built in > 0.13) splits them in to smaller blocks
   Friday, 20 April 12
   

   View Slide

9. Querying
   • Two main interfaces; HTTP & Protocol buffers
   • HTTP API is mainly REST - GET, PUT, DELETE
   • Riak stores the key, value & metadata about the key;
   • Content Type, Charset, Encoding & link data
   • Also: any custom metadata
   Friday, 20 April 12
   

   View Slide

10. Links
    • Used to store one-way relationships between objects;
    • Stored in object meta-data
    • Link-walking uses MapReduce
    Friday, 20 April 12
    

    View Slide

11. MapReduce
    • Designed to be used for web-page-speed requests
    • Built in
    • Map / Reduce functions are written in Javascript or Erlang
    • Can do re-reduce
    • Streaming MapReduce
    Friday, 20 April 12
    

    View Slide

12. Vector clocks
    • Each value is tagged with a vector clock
    • Riak can determine if values;
    • Are direct decendants of a single object
    • Share a common parent
    • Unrelated
    • In Riak each object has a vector clock
    • Cassandra uses timestamps - problems can occur with out of sync
    Friday, 20 April 12
    

    View Slide

13. Siblings
    • Siblings are different versions of the same document which Riak has
    not merged
    • Occurs only if allow_mult is enabled on a bucket AND;
    • Concurrent write with the same vector clock value
    • Stale vector clock
    • No vector clock passed
    Friday, 20 April 12
    

    View Slide

14. Pre & Post Commit Hooks
    • Allow the object to be written
    • Modify the object
    • Fail the update
    • They are per-bucket (stored in the properties)
    • Written in Javascript (pre-hooks) or Erlang (pre/post-hooks)
    Friday, 20 April 12
    

    View Slide

15. Admin
    • Super simple;
    • riak-admin join
    • riak-admin leave
    • Backup tools are provided....
    Friday, 20 April 12
    

    View Slide

16. Backup / restore
    • riak-admin backup|restore [[node|
    all]]
    • Alternative is filesystem backup for bitcask; as it uses append-only files
    • riak-admin backup is storage-engine agnostic
    • riak-admin only backs up kv data; not search indexes (Riak-Search)
    Friday, 20 April 12
    

    View Slide

17. Storage engines
    • Ships with two default storage engines;
    • Bitcask - default, best when keyspace < RAM
    • InnoDB - suggested when keyspace > RAM
    • Also available - Google’s LevelDB. It’s BSD licensed & recently
    integrated, good for large sets.
    Friday, 20 April 12
    

    View Slide

18. Riak-Search
    • Full-text search engine built on top of Riak
    • Realtime
    • Uses Lucene Analyzers, custom ones may be written in Erlang / Java
    • Supports term / field searchs, boolean operators, grouping, lexical
    range queries and end of word wildcards
    • Will be part of Riak as default from 1.0
    Friday, 20 April 12
    

    View Slide

19. Riak > Cassandra
    • Extremely simple to add or remove nodes from a cluster
    • No pre-setup of datamodel
    • Rest & Protobuf API access
    • Commercial support from the original developers, Basho
    Friday, 20 April 12
    

    View Slide

20. Riak = Cassandra
    • No single point of failure
    • Linearly scalable
    • High availability
    • Eventually consistent
    • You can choose your own consistency requirements
    Friday, 20 April 12
    

    View Slide

21. Riak < Cassandra
    • CQL; an SQL-ish language
    • Range / cover queries are built in (no need to write MapReduce functions)
    • ‘Enterprise’ features (dc / rack awareness) are free & in the open-source build
    • Wide support / training from 3rd party commercial parties; DataStax / Acunu / Impetus / Onzra
    http://wiki.apache.org/cassandra/ThirdPartySupport
    • Cassandra is seemly more popular & has a bigger community
    • Partitions vs MD5 of RandomPartitioner; you can’t reconfigure if you need - careful you plan with Riak!
    http://wiki.basho.com/Cluster-Capacity-Planning.html
    Friday, 20 April 12
    

    View Slide

22. Further reading
    • Basho’s slide deck; http://wiki.basho.com/Slide-Decks.html
    • Commit hooks; http://wiki.basho.com/Pre--and-Post-Commit-
    Hooks.html
    • Riak / Cassandra; http://wiki.basho.com/Riak-Compared-to-
    Cassandra.html
    Friday, 20 April 12
    

    View Slide

23. Questions?
    Friday, 20 April 12
    

    View Slide