This document provides an overview and history of the Cassandra Query Language (CQL) and discusses changes between versions 1.0 and 2.0. It notes that CQL was introduced in Cassandra 0.8.0 to provide a more stable and user-friendly interface than the native Cassandra API. Major changes in CQL 2.0 included data type changes and additional functionality like named keys, counters, and timestamps. The document outlines the roadmap for future CQL features and lists several third-party driver projects supporting CQL connectivity.

1. CQL In Cassandra 1.0 (and beyond)
Big Data DC Meetup #5
October 17, 2011
Eric Evans
eric@acunu.com
@jericevans, @acunu

2. ● Overview, history, motivation
● Changes in CQL 2.0 (Cassandra 1.0)
● Coming soon (?)
● Drivers status

3. What?
● Cassandra Query Language
● aka CQL
● aka /ˈsēkwəl/
● Exactly like SQL (except where it's not)
● Introduced in Cassandra 0.8.0
● Ready for production use

4. SQL? Almost.
–- Inserts or updates
INSERT INTO Standard1 (KEY, col0, col1)
VALUES (key, value0, value1)
vs.
–- Inserts or updates
UPDATE Standard1
SET col0=value0, col1=value1 WHERE KEY=key

5. SQL? Almost.
–- Get columns for a row
SELECT col0,col1 FROM Standard1 WHERE KEY=key
–- Range of columns for a row
SELECT col0..colN
FROM Standard1 WHERE KEY=key
–- First 10 results from a range of columns
SELECT FIRST 10 col0..colN
FROM Standard1 WHERE KEY=key
–- Invert the sorting of results
SELECT REVERSED col0..colN
FROM Standard1 WHERE KEY=key

6. Why?

7. Interface Instability

8. (Un)ease of use
Column col = new Column(ByteBuffer.wrap(“name”.getBytes()));
col.setValue(ByteBuffer.wrap(“value”.getBytes()));
col.setTimestamp(System.currentTimeMillis());
ColumnOrSuperColumn cosc = new ColumnOrSuperColumn();
cosc.setColumn(col);
Mutation mutation = new Mutation();
Mutation.setColumnOrSuperColumn(cosc);
List mutations = new ArrayList<Mutation>();
mutations.add(mutation);
Map mutations_map = new HashMap<ByteBuffer, Map<String, List<Mutation>>>();
Map cf_map = new HashMap<String, List<Mutation>>();
cf_map.set(“Standard1”, mutations);
mutations.put(ByteBuffer.wrap(“key”.getBytes()), cf_map)

9. CQL
INSERT INTO Standard1 (KEY, col0)
VALUES (key, value0)

10. Why? How about...
● Better stability guarantees
● Easier to use (you already know it)
● Better code readability / maintainability

11. Why? How about...
● Better stability guarantees
● Easier to use (you already know it)
● Better code readability / maintainability
● Irritates the NoSQL purists

12. Why? How about...
● Better stability guarantees
● Easier to use (you already know it)
● Better code readability / maintainability
● Irritates the NoSQL purists
● (Still )irritates the SQL purists

14. CQL 2.0

15. Wait, 2.0? You call that stable?
Yes yes, but...
● We had a few FUBARs in the first pass
● Not the norm, honest
● It's a mulligan
● Look, cats!

16. Changed in 2.0
● SELECT count(...) FROM now returns row,
not column count
● Terms / Types
● bytea became blob
● int became 4-bytes (was arbitrary precision)
● date became timestamp

17. Also new (but not breaking)
● Named keys (virtual columns)
● Counters
● Complete DDL support
● Timestamps and TTLs

18. Named Keys
–- An unnamed key uses the KEY keyword
CREATE TABLE Standard1
(KEY text PRIMARY KEY)
–- But you can also name one like so...
CREATE TABLE Standard1
(username text PRIMARY KEY)
–- The name will also be used in results!
SELECT email FROM Standard1
WHERE username = 'jericevans'

19. Counters
–- Counter increment
UPDATE Standard1
SET acount = acount + 1 WHERE KEY = key
–- Counter decrement
UPDATE Standard1
SET acount = acount - 1 WHERE KEY = key
–- 1 not enough? Go nuts.
UPDATE Standard1
SET acount = acount + 9 WHERE KEY = key

20. Timestamps and TTLs
–- Inserts or updates
UPDATE CFam USING TIMESTAMP 131851901600
SET col0=value0, col1=value1 WHERE KEY=key
–- Inserts or updates
UPDATE CFam USING TTL 86400
SET col0=value0, col1=value1 WHERE KEY=key

21. Coming Soon(ish)

22. Roadmap
● Prepared statements (CASSANDRA-2475)
● Compound columns (CASSANDRA-2474)
● Custom transport / protocol (CASSANDRA-2478)
● Performance testing (CASSANDRA-2268)
● Schema introspection (CASSANDRA-2477)
● Multiget support (CASSANDRA-3069)

23. Drivers

24. Drivers
● Hosted on Apache Extras (Google Code)
● Tagged cassandra and cql
● Licensed using Apache License 2.0
● Conforming to a standard for database
connectivity (if applicable)
● Coming soon, automated testing and
acceptance criteria

25. Drivers
Driver Platform Status
cassandra-jdbc Java Good
cassandra-dbapi2 Python Good
cassandra-ruby Ruby New
cassandra-pdo PHP New
cassandra-node Node.js Good
http://code.google.com/a/apache-extras.org/hosting/search?q=label%3aCassandra

26. The End