1. Time Series Data With A
Apache Cassandra
ApacheCon Europe
November 18, 2014
Eric Evans
eevans@opennms.org
@jericevans

2. Open

3. Open

4. Open

5. Open

6. Network
Management
System

7. OpenNMS: What It Is
● Network Management System
○ Discovery and Provisioning
○ Service monitoring
○ Data collection
○ Event management, notifications
● Java, open source, GPLv3
● Since 1999

8. Time series: RRDTool
● Round Robin Database
● First released 1999
● Time series storage
● File-based, constant-size, self-maintaining
● Automatic, incremental aggregation

9. … and oh yeah, graphing

10. Consider
● 5+ IOPs per update (read-modify-write)!
● 100,000s of metrics, 1,000s IOPS
● 1,000,000s of metrics, 10,000s IOPS
● 15,000 RPM SAS drive, ~175-200 IOPS

12. Hmmm
We collect and write a great deal; We read
(graph) relatively little.
So why are we aggregating everything?

13. Also
● Not everything is a graph
● Inflexible
● Incremental backups impractical
● Availability subject to filesystem access

14. TIL
Metrics typically appear in groups that are
accessed together.
Optimizing storage for grouped access is a
great idea!

15. What OpenNMS needs:
● High throughput
● High availability
● Late aggregation
● Grouped storage/retrieval

16. Cassandra
● Distributed database
● Highly available
● High throughput
● Tunable consistency

17. SSTables
Writes
Memtable
Commitlog
SSTable
Memory
Disk

18. Write Properties
● Optimized for write throughput
● Sorted on disk
● Perfect for time series!

19. Partitioning Z A
A
B
C
Key: Apple
...

20. Placement
A
B
C
Key: Apple
...

21. Replication
A
B
C
Key: Apple
...

22. CAP Theorem
Consistency
Availability
Partition tolerance

23. Consistency
A
B
?
W=2

24. Consistency
R=2
R+W > N
?
B
C

25. Distribution Properties
● Symmetrical
● Linearly scalable
● Redundant
● Highly available

26. D ata M odel

27. Data Model
resource

28. Data Model
resource
T1 T2 T3

29. Data Model
resource
T1
M1 M2
V1 V2
M3
V3
T2
M1 M2
V1 V2
M3
V3
T3
M1 M2
V1 V2
M3
V3

30. Data Model
CREATE TABLE samples (
T timestamp,
M text,
V double,
resource text,
PRIMARY KEY(resource, T, M)
);

31. Data model
resource T1 M1 V1 T1 M2 V2 T1 M3 V3

32. Data model
resource T1 M1 V1 T1 M2 V2 T1 M3 V3
SELECT * FROM samples
WHERE resource = ‘resource’
AND T = ‘T1’;

33. Data model
resource T1 M1 V1 T1 M2 V2 T1 M3 V3
resource T1 M1 V1

34. Data model
resource T1 M1 V1 T1 M2 V2 T1 M3 V3
T1 M1 V1
T1 M2 V2
resource
resource

35. Data model
resource T1 M1 V1 T1 M2 V2 T1 M3 V3
T1 M1 V1
T1 M2 V2
T1 M3 V3
resource
resource
resource

36. Data model
resource T1 M1 V1 T2 M1 V1 T3 M1 V1
SELECT * FROM samples
WHERE resource = ‘resource’
AND T >= ‘T1’ AND T <= ‘T3’;

37. Newts
● Standalone time series data-store
○ REST server
○ Java API
● Raw sample storage and retrieval
● Flexible aggregations (computed at read)
○ Rate (counter types)
○ Pluggable aggregation functions
○ Arbitrary calculations

38. Newts
● Search-enabled
● Fast; Runs at Cassandra-speed
● Apache licensed
● Github (http://github.com/OpenNMS/newts)
● http://newts.io

39. Fin