This document discusses CQL, the Cassandra Query Language. CQL is designed to be similar to SQL but with some differences to account for Cassandra's data model. The presentation provides an overview of CQL's syntax and capabilities, discusses why CQL was created to provide a more stable interface than Cassandra's native protocol, and analyzes CQL's performance compared to the native protocol. Future roadmap items for CQL are also presented, including prepared statements and custom transports. Available CQL drivers for languages like Java, Python, Ruby, and Node.js are also briefly mentioned.

1. CQL: SQL for Cassandra
Cassandra NYC
December 6, 2011
Eric Evans
eric@acunu.com
@jericevans, @acunu

2. ● Overview, history, motivation
● Performance characteristics
● 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. Performance

16. Thrift RPC
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)

17. Your query, it's a graph

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

19. Hotspot
Quoted string literals
UPDATE table SET 'name' = 'value'
WHERE KEY = 'somekey'

20. Hotspot
Quoted string literals
UPDATE table SET 'name' = 'value'
WHERE KEY = 'somekey'

21. Hotspot
Quoted string literals
UPDATE table SET 'name' = 'value'
WHERE KEY = 'somekey'
● Anything that appears between quotes
● Inlined Java constructs a StringBuilder to store
the contents (slow not fast)
● Incurred multiple times per statement

22. Hotspot
Marshalling
UPDATE table SET 'clear' = 'abffaadd10'
WHERE KEY = 'acfe12ff'

23. Hotspot
Marshalling
UPDATE table SET 'clear' = 'abffaadd10'
WHERE KEY = 'acfe12ff'
ascii blob

24. Hotspot
Marshalling
UPDATE table SET 'clear' = 'abffaadd10'
WHERE KEY = 'acfe12ff'
ascii blob
● Terms are marshalled to bytes by type
● String.getBytes is slow (AsciiType)
● Hex conversion is fast faster (BytesType)
● Incurred multiple times per statement

25. Hotspot
Copying / Conversion
execute_cql_query(
ByteBuffer query, enum compression)
● Query is binary to support compression (is it worth it?)
● And don't forget the String → ByteBuffer conversion on
the client-side
● Incurred only once per statement!

26. Achtung!
(These tests weren't perfect)
● Uneeded String → ByteBuffer → String
● No query compression implemented
● Co-located client and server

27. Insert 20M rows, 5 columns
Avg rate Avg latency
RPC 20,953/s 1.6ms
CQL 19,176/s (-8%) 1.7ms (+9%)

28. Insert 10M rows, 5 cols (indexed)
Avg rate Avg latency
RPC 9,850/s 5.3ms
CQL 9,290/s (-6%) 5.5ms (+4%)

29. Counts, 10M rows, 5 cols
Avg rate Avg latency
RPC 18,052/s 1.7ms
CQL 17,635/s (-2%) 1.7ms

30. Reading 20M rows, 5 cols
Avg rate Avg latency
RPC 22.726/s 2.0ms
CQL 20,272/s (-11%) 2.3ms (+10%)

31. In Summary
Don't step over dollars to pick up pennies!

32. Coming Soon(ish)

33. 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)

34. Drivers

35. 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

36. 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

37. The End