Cassandra: Not Just NoSQL, It's MoSQL

Not just NoSQL, It’s MoSQL Cassandra SF July 11, 2011 Eric Evans eevans@rackspace.com @jericevans http://blog.sym-link.com

Cassandra Query Language● Structured query language for Apache Cassandra.● CQL for short (pronounced /siːkw əl/).● SQL alike (best effort).● An alternative to the existing API, not a replacement (not yet).● Available for use in Cassandra 0.8.0.

Wait, arent you the guy...?

So, is this a troll?

Problem?

Naw.(not a troll, honest)

But, why?

Because the API sucks.

“Thrift sucks, ergo the API sucks”● Generated code (C++ compiler).● Loads of languages, but varying levels of support. ● PHP anyone?● Upstream alternating between extremes of combativeness and apathy. ● Patches ignored, (or refused). ● Loads of (serious )bugs ignored for long periods. ● Infrequent releases.

“Avro Does Not Suck, so...”1. Avro2. Something, something, something3. Profit!

And the API still sucks.

Brass Tacks● Unstable ● Too tightly coupled to internal APIs● Too difficult to use ● Not enough abstraction (and passing the buck to 3rd-party API maintainers is weak) ● Poor mental fit for query/data models

Back to the drawing board● RPC (Thrift, Avro, Protobuf, etc)● REST● Query language● Etc, etc

Back to the drawing board● RPC (Thrift, Avro, Protobuf, etc) ● Easy to implement ● Performant● REST● Query language● Etc, etc

Back to the drawing board● RPC (Thrift, Avro, Protobuf, etc) ● Easy to implement ● Performant● REST ● Little need for client abstraction● Query language● Etc, etc

Back to the drawing board● RPC (Thrift, Avro, Protobuf, etc) ● Easy to implement ● Performant● REST ● Little need for client abstraction● Query language ● Little need for client abstraction! ● Reads well; What you see is what you get ● The Devil we all know● Etc, etc

Grok Thisfirstname = Column(name="firstname", value="Eric", timestamp=time)firstcosc = ColumnOrSuperColumn(column=firstname)lastname = Column(name="lastname", value="Evans", timestamp=time)lastcosc = ColumnOrSuperColumn(column=lastname)mutations = []mutations.append(Mutation(column_or_supercolumn=firstcosc))mutations.append(Mutation(column_or_supercolumn=lastcosc))client.batch_mutate(mutation_map={"eevans": {"table": mutations}}, consistency_level=ConsistencyLevel.ONE)

What about this?UPDATE tableSET firstname=Eric, lastname=EvansWHERE KEY=eevans

Grok Thisparent = ColumnParent(column_family="table")colnames = ["firstname", "lastname"]predicate = SlicePredicate(column_names=colnames)row = client.get_slice(key="eevans", column_parent=parent, predicate=predicate, consistency_level=CL.ONE)

And this?SELECT firstname, lastnameFROM tableWHERE KEY = eevans

Lessons Learned● Know when to take a step back● Listen to your users; Read between the lines● Beware quick/easy consensus● Just because its old doesnt mean its bad● Just because its the brunt of jokes, doesnt make it wrong (works for Thrift and SQL)

Language● Versioned specification (http://semver.og) ● Major – Breaking changes, (rare to never) ● Minor – Backward compatible changes ● Patch – Bug fixes

Drivers● Maintained and distributed by us● Separate development cycles; Separately versioned● Support a language version, not a Cassandra version!● Minimal, low-level (not the place for an ORM)● Idiomatic● client-dev@cassandra.apache.org

More Info● Docs (doc/cql/CQL.html)● http://www.datastax.com/docs/0.8/api/using_cql● http://caqel.deadcafe.org (live demo!)● cqlsh (interactive shell shipped w/ Python driver)

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Cassandra: Not Just NoSQL, It's MoSQL

by Eric Evans

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