State of CQL talk at the Cassandra EU summit

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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CQL distinguishes 2 sub-parts in the PRIMARY KEY:
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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CL
Q

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
CL
Q

12. New in Cassandra 2.0
Conditional DDL:
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DO KYPC I EIT k;
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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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CL
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Limited SELECT DISTINCT:
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13/20
CL
Q

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
JV
AA

16. New in Cassandra 2.0: native protocol 2
Cursors:
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e s o . x c t ( I S R N O s r i , h t ) A U S ? ) , o e d h t B t sA A
)
;
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?)