Speaker: Sylvain Lebresne, Software Engineer at DataStax Video: http://www.youtube.com/watch?v=4GSfAS4nFAs&list=PLqcm6qE9lgKLoYaakl3YwIWP4hmGsHm5e&index=18 Since its inception, the Cassandra Query Language (CQL) has grown and matured, resulting in the 3rd version of the language (CQL3) being finalized in Cassandra 1.2 and further improved in Cassandra 2.0. Compared to the legacy Thrift API, CQL3 aims at providing an API that is higher level, more user friendly, but still fully assumes the distributed nature of Cassandra and it's storage engine. This talk will present CQL3, describing the reasoning and goals behind the language as well as the language itself. We will also touch on CQL's relationship with Thrift and will present the CQL binary protocol that has been introduced in Cassandra 1.2. We will wrap up by discussing the future of CQL.

1. The State of CQL
Sylvain Lebresne (DataStax)

2. A short CQL primer
New in Cassandra 2.0
Native protocol
What's next?
2/20

3. A better API for Cassandra
Thrift is not satisfactory:
· Not user friendly, hard to use.
· Low level, very little abstraction.
· Hard to evolve (in a backward compatible way).
· Unreadable without driver abstraction.
Cassandra has often been regarded as hard to develop against.
It doesn't have to be that way!
3/20

4. Quick historical notes
· CQL1 first introduced in Cassandra 0.8, became CQL2 in Cassandra 1.0
· "These aren't the CQL you are looking for"
· CQL3 (CQL for short thereafter) introduced in Cassandra 1.2
· Semantically, CQL1/CQL2 are closer to the Thrift API than to CQL3.
· CQL3 is the version that's here to stay: no plan for a CQL4 any time soon.
4/20

5. A short CQL primer

6. The Cassandra Query Language
· Syntactically, a subset of SQL (with a few extensions)
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· INSERT and UPDATE are both upserts
· No joins, no sub-queries, no aggregation, ...
· Denormalization is the norm: do the work at write time, not read time
6/20
CL
Q

7. Denormalization: Cassandra modeling 101
Efficient queries in Cassandra are based on 2 principles:
· the data queried is collocated on one replica set
· the data queried is collocated on disk on those replicas
Denormalization is the technique that allows to achieve this in practice.
But this means CQL exposes:
· how to collocate data on the same replica set
· how to collocate data on disk (for a given replica)
7/20

8. This is done in CQL through the primary key
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partition key: decides the node on which the data is stored
clustering columns: within the same partition key, (CQL3) rows are
physically ordered following the clustering columns
·
·
This is important, because CQL only allow queries for which an explicit index
exists:
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8/20
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9. CQL main features
· Collections (set, map and list)
· Secondary indexes
· Convenience functions (timeuuid, type conversions, ...)
· ...
For more details:
· http://cassandra.apache.org/doc/cql3/CQL.html
· http://www.datastax.com/documentation/cql/3.1/webhelp/index.html
9/20

10. New in Cassandra 2.0

11. New in Cassandra 2.0
Lightweight transactions:
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ALTER DROP:
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11/20
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12. New in Cassandra 2.0
Conditional DDL:
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Secondary indexes everywhere (almost):
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12/20
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13. Coming in Cassandra 2.0.2
Named bind variables:
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Limited SELECT DISTINCT:
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13/20
CL
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14. The native protocol
A binary transport protocol for CQL

15. Native protocol
· Binary transport protocol for CQL
· Query execution, prepared statements, authentication, compression, ...
· Asynchronous (allows multiple concurrent queries per connection)
· Server notifications (Only generic cluster events currently)
· Existing drivers for Java, C#, Python, C++, Golang, ...
Example usage of the Java driver (https://github.com/datastax/java-driver):
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15/20
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16. New in Cassandra 2.0: native protocol 2
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;
SASL for authentication
16/20

17. What's next?
Cassandra 2.1 and beyond

18. CQL: some ideas
· Storage engine optimizations for CQL
· Secondary index for collections
· Server side functions
· User defined types
· ...
18/20

19. User defined types
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19/20
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20. Thank You!
(Questions?)