cassandra eu 2012 - cql: then, now and when by eric evans

CQL: Then, Now, and When

Eric [email protected]

Cassandra EuropeMarch 28, 2012

Wednesday, March 28, 12

mailto:[email protected]

mailto:[email protected]

• Query language for Apache Cassandra

• SQL for the most part

• An alternative query interface

• Available since Cassandra 0.8.0

Cassandra Query Language(aka CQL)


Best Troll Ever?


Not a troll at all, actually.


• RPC-based query interface

• Low level; very little abstraction

• Implemented in Thrift

• Compact binary serialization

• Loads of supported languages

• Generated language code

Status Quo


Unstable$@#*!

NOT AGAIN!

Relax

It’ll take you 5 minutes toupdate your code.


Not User Friendly


This cannot be unseen!// Your columnColumn col = new Column(ByteBuffer.wrap(“name”.getBytes()));col.setValue(ByteBuffer.wrap(“value”.getBytes()));col.setTimestamp(System.currentTimeMillis());

// Don’t askColumnOrSuperColumn cosc = new ColumnOrSuperColumn();cosc.setColumn(cosc);

// Hang on, here we go...Mutation mutation = new Mutation();mutation.setColumnOrSuperColumn(cosc);

List<Mutation> mutations = new ArrayList<Mutation>();mutations.add(mutation);

Map mutations_map = new HashMap<ByteBuffer, Map<String, List<Mutation>>>();Map cf_map = new Map<String, List<Mutation>>();cf_map.set(“Standard1”, mutations);mutations_map.put(ByteBuffer.wrap(“key”.getBytes()), cf_map);

cassandra.batch_mutate(mutations_map, consistency_level);


A query interface should be...

Simple

Intuitive

Invisible

Performant(?)


Alternatives

• REST

• RPC (Thrift, Avro, Protobuf, etc)

• SQL (bahahaha)

• etc, etc


REST

Pros Cons

• Ubiquitous

• Frequently requested

• Client uniformity

• Fails expectations

• Slow


RPC

Pros Cons

• Easy to implement

• Performant

• Poor mental fit

• Heavy dependency


SQL

Pros Cons

• Ubiquitous

• Widely known

• Excellent mental fit

• Client uniformity

• People whinging

• Security(?)


Hello...-- Create or updateINSERT INTO users (id, given, surname) VALUES (jericevans, Eric, Evans);

-- Create or updateUPDATE users SET given = Eric, surname = Evans WHERE id = jericevans;

SELECT surname, given FROM users WHERE id = jericevans;


-- Adding an indexCREATE INDEX surnameidx ON users (surname);

SELECT id, given FROM users WHERE surname = Evans;

-- Limiting the number of rowsSELECT id, given FROM users WHERE surname = Evans LIMIT 1000;

...is it me you’re looking for?


-- From column, to columnSELECT ‘2012-01-01’..’2012-03-28’ FROM NewsWHERE topic = cassandra

-- Last N columnsSELECT FIRST 10 REVERSED * FROM NewsWHERE topic = cassandra

Querying column ranges


-- Get your count onUPDATE inventory SET apples = apples + 1 WHERE id = fruit;

UPDATE inventory SET carrots = carrots - 1 WHERE id = vegetable;

Counting


BEGIN BATCH INSERT INTO msgs (owner, subject, body) VALUES(jericevans, ‘Hi’, ‘Howdy’); UPDATE subjects SET subject = now WHERE owner = jericevansAPPLY BATCH

Batching writes



Simple

Intuitive

Invisible

Performant(?)


Drivers• Not a replacement for high-level, idiomatic

libraries

• Avoids duplicating efforts, (error handling, pooling, etc)

• Consistently scoped, JDBC, etc

• Consistently hosted, licensed

• Discoverable

• More work needed...


Current lineup

• JDBC (Java)

• DB-API 2 (Python)

• PDO (PHP)

• Ruby

• Node.JS


And what about interfacestability?


CQL 1.0

0.8.0


CQL 2.0

0.8.01.0.0

• types made more consistent w/ SQL• count() returns rows, not columns


CQL 3.0

0.8.01.0.0

1.1.0


CQL 3.0-- A materialized timeline of tweetsCREATE COLUMNFAMILY timeline ( username text, posted_at timestamp, body text, posted_by text, PRIMARY KEY (username, posted_at));


CQL 3.0INSERT INTO timeline (username, posted_at, body, posted_by)VALUES (scotty, ‘2012-03-23 14:36’ ‘stupid klingons...’, jtkirk);

INSERT INTO timeline (username, posted_at, body, posted_by)VALUES (scotty, ‘2012-03-23 16:12’ ‘@jtkirk green?’, spock);

INSERT INTO timeline (username, posted_at, body, posted_by)VALUES (scotty, ‘2012-03-23 17:42’ ‘@spock yes, green’, jtkirk);

INSERT INTO timeline (username, posted_at, body, posted_by)VALUES (scotty, ‘2012-03-25 08:14’ ‘get off my lawn!’, bones);


In Cassandra’s eyes eye

scotty(23/03 14:36, body):

stupid klingons...(23/03 14:36, posted_by):

jtkirk(23/03 16:12, body):

@jtkirk green?...


-- Tweets in Scotty’s timeline, by dateSELECT * FROM timeline WHERE username = scotty AND posted_at > ‘2012-03-22’;


Is it a row, or a table?Yes.

username posted_at body posted_by

scotty 23/03 14:36 stupid klingons... jtkirk

scotty 23/03 16:12 @jtkirk green? spock

scotty 23/03 17:42 @spock yes, green jtkirk

scotty 25/03 08:14 get off my lawn! bones


Also...

• Column names are strictly UTF-8

• Column names are case-insensitive (unless quoted)

• Old slice notation is gone (<start>..<end>)

• Static column families are actually static (schema-enforced)


$@#*!

NOT AGAIN!


CQL 2.0 + 3.0 “beta”

0.8.01.0.0

1.1.0

You arehere


CQL 3.0

0.8.01.0.0

1.1.0

You will be here

1.2.0



Simple

Intuitive

Invisible

Performant(?)


Performanceinserts


Performanceinserts w/ index


Performancecounter increments


Performancereads



Simple

Intuitive

Invisible

Performant


Help Wanted

• Writing tests

• Documentation

• Feedback

• Drivers


cassandra eu 2012 - cql: then, now and when by eric evans

Technology

new arraylistmutations

new mapcf

new mutationmutation

new columnbytebuffer

new columnorsupercolumncosc

new hashmapmap cf

users id

userswhere id