How does Riak compare to Cassandra? [Cassandra London User Group July 2011]

RiakHow does Riak compare to Cassandra?

/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

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)

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

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)

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)

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

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

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

Links• Used to store one-way relationships between objects;• Stored in object meta-data• Link-walking uses MapReduce

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

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

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

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)

Admin• Super simple;• riak-admin join <node-in-cluster>• riak-admin leave• Backup tools are provided....

Backup / restore• riak-admin backup|restore <node> <cookie> <output_file> [[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)

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.

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

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

Riak = Cassandra• No single point of failure• Linearly scalable• High availability• Eventually consistent• You can choose your own consistency requirements

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

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

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How does Riak compare to Cassandra? [Cassandra London User Group July 2011]

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