An introduction to indexing with supercolumns and range queries in Cassandra.

1. Cassandra Basics
Indexing
Benjamin Black, b@b3k.us

2. Relational stores are
SCHEMA ORIENTED

3. Start from your SCHEMA &
WORK FORWARDS

4. Column stores are
QUERY ORIENTED

5. Start from your QUERIES &
WORK BACKWARDS

6. AT SCALE

7. AT SCALE
Denormalization is
THE NORM

8. AT SCALE

9. AT SCALE
Everything depends on
THE INDICES

10. Cassandra is an
INDEX CONSTRUCTION KIT

11. Column Family

12. Two-level Map
key: {
column: value,
column: value,
...
}

13. Super Column Family

14. Three-level Map
key: {
supercolumn: {
column:value,
column: value
},
supercolumn: {
...
}
}

15. column sorting defined by
CompareWith/
CompareSubcolumnsWith

16. TimeUUIDType
UTF8Type
ASCIIType
LongType
LexicalUUIDType

17. row placement determined by
Partitioner

18. RandomPartitioner
Place based on MD5 of key
OrderPreservingPartitioner
Place based on actual key

19. Rows are sorted by key on each node
Regardless of partitioner

20. One example in
TWO ACTS

21. Prelude
A USER DATABASE

22. <ColumnFamily Name=”Users”
CompareWith=”UTF8Type” />

23. “b”: {“name”:”Ben”, “street”:”1234 Oak St.”,
“city”:”Seattle”, “state”:”WA”}
“jason”: {”name”:”Jason”, “street”:”456 First Ave.”,
“city”:”Bellingham”, “state”:”WA”}
“zack”: {”name”: “Zack”, “street”: “4321 Pine St.”,
“city”: “Seattle”, “state”: “WA”}
“jen1982”: {”name”:”Jennifer”, “street”:”1120 Foo Lane”,
“city”:”San Francisco”, “state”:”CA”}
“albert”: {”name”:”Albert”, “street”:”2364 South St.”,
“city”:”Boston”, “state”:”MA”}

24. SELECT name FROM Users
WHERE state=”WA”

25. SELECT name FROM Users
WHERE state=”WA”
How is WHERE clause
formed?

26. Act One
Supercolumn Indexing

27. <ColumnFamily Name=”LocationUserIndexSCF”
CompareWith=”UTF8Type”
CompareSubcolumnsWith=”UTF8Type”
ColumnType=”Super” />

28. [state]: {
[city1]: {[name1]:[user1], [name2]:[user2], ... },
[city2]: {[name3]:[user3], [name4]:[user4], ... },
...
[cityX]: {[name5]:[user5], [name6]:[user6], ... }
}

29. “CA”: {
“San Francisco”: {”Jennifer”: “jen1982”}
}
“MA”: {
“Boston”: {”Albert”: “albert”}
}
“WA”: {
“Bellingham”: {”Jason”: “jason”},
“Seattle”: {”Ben”: “b”, ”Zack”: “zack”}
}

30. Row Key
“CA”: {
“San Francisco”: {”Jennifer”: “jen1982”}
}
“MA”: {
“Boston”: {”Albert”: “albert”}
}
“WA”: {
“Bellingham”: {”Jason”: “jason”},
“Seattle”: {”Ben”: “b”, ”Zack”: “zack”}
}

31. Row Key
Super Column
“CA”: {
“San Francisco”: {”Jennifer”: “jen1982”}
}
“MA”: {
“Boston”: {”Albert”: “albert”}
}
“WA”: {
“Bellingham”: {”Jason”: “jason”},
“Seattle”: {”Ben”: “b”, ”Zack”: “zack”}
}

32. Row Key
Colum
Super Column
n
“CA”: {
“San Francisco”: {”Jennifer”: “jen1982”}
}
“MA”: {
“Boston”: {”Albert”: “albert”}
}
“WA”: {
“Bellingham”: {”Jason”: “jason”},
“Seattle”: {”Ben”: “b”, ”Zack”: “zack”}
}

33. Row Key
Colum
Super Column Value
n
“CA”: {
“San Francisco”: {”Jennifer”: “jen1982”}
}
“MA”: {
“Boston”: {”Albert”: “albert”}
}
“WA”: {
“Bellingham”: {”Jason”: “jason”},
“Seattle”: {”Ben”: “b”, ”Zack”: “zack”}
}

34. Show me
EVERYONE IN WASHINGTON

35. get(:LocationUserIndexSCF, ‘WA’)

36. {
“Bellingham”: {”Jason”: “jason”},
“Seattle”: {”Ben”: “b”, ”Zack”: “zack”}
}

37. Act Two
Composite Key Indexing

38. Order Preserving Partitioner
+
Range Queries

39. <ColumnFamily Name=”LocationUserIndexCF”
CompareWith=”UTF8Type” />

40. [state1]/[city1]: {[name1]:[user1], [name2]:[user2], ... }
[state1]/[city2]: {[name3]:[user3], [name4]:[user4], ... }
[state2]/[city1]: {[name5]:[user5], [name6]:[user6], ... }
...
[stateX]/[cityY]: {[name7]:[user7], [name8]:[user8], ... }

41. “CA/San Francisco”: {”Jennifer”: “jen1982”}
“MA/Boston”: {”Albert”: “albert”}
“WA/Bellingham”: {”Jason”: “jason”}
“WA/Seattle”: {”Ben”: “b”, “Zack”: “zack”}

42. Show me
EVERYONE IN WASHINGTON

43. get_range(:LocationUserIndexCF, {:start: 'WA',
:finish:'WB'})

44. {
”WA/Bellingham”: {”Jason”: “jason”},
“WA/Seattle”: {”Ben”: “b”, “Zack”: “zack”}
}

45. Finale
BUILD SOMETHING AWESOME

46. (This part is up to you)

47. Appendix
EXAMPLE KEYSPACE

48. <Keyspace Name="UserDb">
<ColumnFamily Name="Users"
CompareWith="UTF8Type" />
<ColumnFamily Name="LocationUserIndexSCF"
CompareWith="UTF8Type"
CompareSubcolumnsWith="UTF8Type"
ColumnType="Super" />
<ColumnFamily Name="LocationUserIndexCF"
CompareWith="UTF8Type" />
<ReplicaPlacementStrategy>
org.apache.cassandra.locator.RackUnawareStrategy
</ReplicaPlacementStrategy>
<ReplicationFactor>1</ReplicationFactor>
<EndPointSnitch>org.apache.cassandra.locator.EndPointSnitch</EndPointSnitch>
</Keyspace>