CQL: SQL In Cassandra
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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.
CQL: SQL In Cassandra
- 1. CQL: SQL for Cassandra Cassandra NYC December 6, 2011 Eric Evans [email protected] @jericevans, @acunu
- 2. ā Overview, history, motivation ā Performance characteristics ā Coming soon (?) ā Drivers status
- 3. What? ā Cassandra Query Language ā aka CQL ā aka /ĖsÄkwÉl/ ā Exactly like SQL (except where it's not) ā Introduced in Cassandra 0.8.0 ā Ready for production use
- 4. SQL? Almost. ā- Inserts or updates INSERT INTO Standard1 (KEY, col0, col1) VALUES (key, value0, value1) vs. ā- Inserts or updates UPDATE Standard1 SET col0=value0, col1=value1 WHERE KEY=key
- 5. SQL? Almost. ā- Get columns for a row SELECT col0,col1 FROM Standard1 WHERE KEY=key ā- Range of columns for a row SELECT col0..colN FROM Standard1 WHERE KEY=key ā- First 10 results from a range of columns SELECT FIRST 10 col0..colN FROM Standard1 WHERE KEY=key ā- Invert the sorting of results SELECT REVERSED col0..colN FROM Standard1 WHERE KEY=key
- 6. Why?
- 8. (Un)ease of use Column col = new Column(ByteBuffer.wrap(ānameā.getBytes())); col.setValue(ByteBuffer.wrap(āvalueā.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(āStandard1ā, mutations); mutations.put(ByteBuffer.wrap(ākeyā.getBytes()), cf_map)
- 9. CQL INSERT INTO Standard1 (KEY, col0) VALUES (key, value0)
- 10. Why? How about... ā Better stability guarantees ā Easier to use (you already know it) ā Better code readability / maintainability
- 11. Why? How about... ā Better stability guarantees ā Easier to use (you already know it) ā Better code readability / maintainability ā Irritates the NoSQL purists
- 12. Why? How about... ā Better stability guarantees ā Easier to use (you already know it) ā Better code readability / maintainability ā Irritates the NoSQL purists ā (Still )irritates the SQL purists
- 14. Performance
- 16. Thrift RPC Column col = new Column(ByteBuffer.wrap(ānameā.getBytes())); col.setValue(ByteBuffer.wrap(āvalueā.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(āStandard1ā, mutations); mutations.put(ByteBuffer.wrap(ākeyā.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' ā Anything that appears between quotes ā Inlined Java constructs a StringBuilder to store the contents (slow not fast) ā 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 ā Terms are marshalled to bytes by type ā String.getBytes is slow (AsciiType) ā Hex conversion is fast faster (BytesType) ā Incurred multiple times per statement
- 25. Hotspot Copying / Conversion execute_cql_query( ByteBuffer query, enum compression) ā Query is binary to support compression (is it worth it?) ā And don't forget the String ā ByteBuffer conversion on the client-side ā Incurred only once per statement!
- 26. Achtung! (These tests weren't perfect) ā Uneeded String ā ByteBuffer ā String ā No query compression implemented ā 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 ā Prepared statements (CASSANDRA-2475) ā Compound columns (CASSANDRA-2474) ā Custom transport / protocol (CASSANDRA-2478) ā Performance testing (CASSANDRA-2268) ā Schema introspection (CASSANDRA-2477) ā Multiget support (CASSANDRA-3069)
- 34. Drivers
- 35. Drivers ā Hosted on Apache Extras (Google Code) ā Tagged cassandra and cql ā Licensed using Apache License 2.0 ā Conforming to a standard for database connectivity (if applicable) ā 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