very good db material

1. Parallel and distributed databases
R & G Chapter 22

2. What is a distributed database?

3. Why distribute a database
 Scalability and performance
 Resilience to failures
Throughput
Data
size
versus
X X

4. Why distribute a database
 Data is already distributed
 Or needs to be distributed
 Data is in multiple systems

5. Why not distribute a database
You must earn your complexity!
 Communication needed
 Must build a complex infrastructure
 Unpredictable latencies must be masked
 More types of failures
 More components to fail
 Network failures
 Congestion, timeouts
 More complex planning
 Communication cost plus I/O cost
 May have to deal with heterogeneity
 Different types of systems
 Different schemas, possibly incompatible
 Different administrative domains

6. Types of distributed databases

7. The old days: mainframes
Definitely not distributed!

8. Client-server
User interaction
Data processing
Network

9. Parallel database

10. Primary/secondary
X

11. Multidatabase

12. How do they work?
 What is shared?
 How to distribute the data?
 How to process the data?
 How to update the data?

13. What is shared?
 Memory
CPUs RAM Disk
Most modern DBMSs

14. What is shared?
 Disk
RAM
Oracle RAC

15. What is shared?
 Nothing
RAM
Search engines, Teradata

16. Server 1 Server 2 Server 3 Server 4
Bike $86
6/2/07 636353
Chair $10
6/5/07 662113
How to distribute the data?
Couch $570
6/1/07 424252
Car $1123
6/1/07 256623
Lamp $19
6/7/07 121113
Bike $56
6/9/07 887734
Scooter $18
6/11/07 252111
Hammer $8000
6/11/07 116458

17. How to distribute the data?
Hash partitioning Range partitioning
(key,value)
Hash()
(key,value)
<= X > X

18. Server 1 Server 2 Server 3 Server 4
How to distribute the data?
Bike
Chair
Couch
Car
Lamp
Bike
Scooter
Hammer
$86
$10
$570
$1123
$19
$56
$18
$8000
6/2/07
6/5/07
6/1/07
6/1/07
6/7/07
6/9/07
6/11/07
6/11/07
636353
662113
424252
256623
121113
887734
252111
116458

19. Query processing
 Intra-operator parallelism
 Inter-operator parallelism

20. Parallel scanning
filter filter filter filter filter filter
Result

21. Sorting

22. Sorting

23. Parallel hash join
Hash()

24. Join

25. Semi-join

26. Inter-operator parallelism

27. Updating distributed data
 Synchronous: read-any-write-all
Reads are fast

28. Updating distributed data
 Synchronous: voting

29. Updating distributed data
 Synchronous: voting
Writes tolerant to disconnection

30. Consistency of distributed data
 Should provide ACID

31. Primary/secondary

32. Two-phase commit
PREPARE
PREPARED PREPARED
COMMIT

33. Two-phase commit
PREPARE
PREPARED ABORT
ABORT

34. Two-phase commit
PREPARE
PREPARED
ABORT

35. Two-phase commit
PREPARE
PREPARED PREPARED
X

36. Conclusion
 Parallelism and distribution very useful
 Performance
 Fault tolerance
 Scale
 But complex!
 Rethink lots of aspects of the system
 Must earn the complexity