Cassandra EU 2012 - CQL: Then, Now and When by Eric Evans

CQL: Then, Now, and
When

Eric Evans
eric@acunu.com

Cassandra Europe
March 28, 2012

Wednesday, March 28, 12

Cassandra Query Language
(aka CQL)

• Query language for Apache Cassandra
• SQL for the most part
• An alternative query interface
• Available since Cassandra 0.8.0


Best Troll Ever?

Not a troll at all,
actually.


Status Quo
• RPC-based query interface
• Low level; very little abstraction
• Implemented in Thrift
• Compact binary serialization
• Loads of supported languages
• Generated language code

Unstable
$@#*!
Relax

NOT AGAIN!

It’ll take you 5 minutes to
update your code.


Not User Friendly


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

// Don’t ask
ColumnOrSuperColumn 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 • Fails expectations

• Frequently requested • Slow

• Client uniformity


RPC
Pros Cons
• Easy to implement • Poor mental ﬁt

• Performant • Heavy dependency


SQL
Pros Cons
• Ubiquitous • People whinging

• Widely known • Security(?)

• Excellent mental ﬁt

• Client uniformity


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

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

SELECT surname, given FROM users
WHERE id = jericevans;


...is it me you’re looking
for?
-- Adding an index
CREATE INDEX surnameidx ON users (surname);

SELECT id, given FROM users
WHERE surname = Evans;

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


Querying column ranges
-- From column, to column
SELECT ‘2012-01-01’..’2012-03-28’ FROM News
WHERE topic = cassandra

-- Last N columns
SELECT FIRST 10 REVERSED * FROM News
WHERE topic = cassandra


Counting

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

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


Batching writes

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


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 interface
stability?


CQL 1.0

0.
8.
0


CQL 2.0

0. 1.
8. 0.
0 0

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


CQL 3.0

0. 1. 1.
8. 0. 1.
0 0 0


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


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

VALUES (scotty, ‘2012-03-23 16:12’ ‘@jtkirk green?’, spock);

VALUES (scotty, ‘2012-03-23 17:42’ ‘@spock yes, green’, jtkirk);

VALUES (scotty, ‘2012-03-25 08:14’ ‘get off my lawn!’, bones);


In Cassandra’s eyes eye

(23/03 14:36, body): (23/03 14:36, posted_by): (23/03 16:12, body):
scotty ...
stupid klingons... jtkirk @jtkirk green?


-- Tweets in Scotty’s timeline, by date
SELECT * 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”
You are
here

0. 1. 1.
8. 0. 1.
0 0 0


CQL 3.0
You will
be here

0. 1. 1. 1.
8. 0. 1. 2.
0 0 0 0


Performance
inserts


Performance
inserts w/ index


Performance
counter increments


Performance
reads


A query interface
should be...
Simple
Intuitive
Invisible
Performant


Help Wanted

• Writing tests
• Documentation
• Feedback
• Drivers


Cassandra EU 2012 - CQL: Then, Now and When by Eric Evans

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Cassandra EU 2012 - CQL: Then, Now and When by Eric Evans