1. Peer-To-Peer Data Management
Hector Garcia-Molina
ICDE Conference, February 28, 2002

2. ? What is P2P? pastry can jxta fiorana napster freenet united devices
open cola ?
aim
ocean store
netmeeting
gnutella
farsite
icq
maorpheus
ebay
limewire
bearshare
uddi
grove
jabber
popular power
kazaa
tapestry
process tree
mojo nation
chord

3. Napster
join
query
answer
get
file
central index
...

4. Gnutella
query

5. Morpheus
...
...
...
...
super peer
...
...

6.
satellite dish
raw data chunk
analyzed data
central site
...

7. Lockss D3 D1
library D
library A D2
library C
library B
library E

8. PeerCast
Stanford
source
after:
before:
Stanford
source

9. What is a P2P System? Multiple sites (at edge) Distributed resources
Sites are autonomous (different owners)
Sites are both clients and servers
Sites have equal functionality
P2P Purity

10. P2P is BAD IDEA!! Distribution is expensive!
Specialized functionality is good!

11. Example: Distributed Data Management
Distribution is expensive
If you must distribute:
build centralized directory, index
use backups for reliability
for replicated data, use primary copy

12. Computational Efficiency is NOT Main Goal
Main driving force in a P2P system:
exploiting existing (often free) resources
sharing costs among many
legal protection
autonomy
anonymity

13. Should We Do P2P Research?
Should we help people break the law?
Analogy: Should we develop pillows, knives, hammers, drugs, bath tubs, cars, airplanes, ... ??

14. Should We Do P2P Research?
YES: P2P not exclusively for breaking law
Remember the VCR
YES: P2P can liberate us from culture “plantation owners” (Lessig)

15. Is “Free Culture’’ Feasible?
Example: Legal texts
Can we afford it?
economic
activity
rules of the game
today

16. Should DB community work on P2P?
YES

17. P2P Challenges Easier to list NON-Research-Topics:
Color schemes for P2P Nodes
Impact of P2P on Moroccan 15th Century Literature

18. P2P Challenges
Search
Resource Management
Security & Privacy

19. Search Taxonomy lookup freenet can partial replicated SP
content queries
search
gnutella
morpheus
napster
routing
single site
regional
global
scope of index

20. Index Implementation Taxonomy
routing
replicated SP
freenet
yes
gnutella
morpheus
index location correlated
with content location
partial no
napster
can
centralized
distributed
P2P
nature of index

21. Content Addressable Network (CAN)
Nodes 1
Data 2

22. Can We Improve Flooding?
routing
replicated SP
freenet
yes
gnutella
morpheus
index location correlated
with content location
partial no
napster
can
centralized
distributed
P2P
nature of index

23. Directed BFS in Gnutella?
...
query
Heuristics for Selecting Direction
>RES: Returned most results
<TIME: Shortest satisfaction time
<HOPS: Min hops for results
>MSG: Sent us most messages (all types)
<QLEN: Shortest queue
<LAT: Shortest latency
>DEG: Highest degree

24. How Does One Evaluate? Live Gnutella?
Use real Gnutella as “laboratory”

25. Time to Satisfaction for Directed BFS

26. Routing Index C Q(DB) A B D 50 25 C AI DB 20 65 B 70 75 50 90 20 A AIA AI DB 50 B AI DB D 15 D 20 A 50 25 C 15 D AI DB

27. Types of Routing Indexes
Compound
Hop Count
Exponential Decay
Strategies for Cycles
Ignore (for Hop-Count, exponential)
Avoid Update Cycles
Detect Update Cycles and Recover

28. Effect of Index Compression

29. Effect of Network Topology

30. Resource Management Resource: Issues: storage (lockss)
CPU processing
bandwidth (PeerCast)
Issues:
fairness
load balancing

31. A1 B1 C1 A2 B2 C2 B1 A1 B2 A2 Example: Data Trading site 1 site 2
trade B2 A2
trade

32. A1 B1 C1 A2 B2 C2 B1 A1 C1 A2 C2 B2 Example: Data Trading site 1
trade C1 A2
trade C2 B2
trade

33. Data Trading Order of trades impacts reliability Issues:
Swaps vs. Deeds
Fixed price vs. bids
Preference to
sites with a lot of space?
reliable sites?
“desperate” sites?

34. Effect of Bid Policies bid more (ask more in return)
when I have less free space
bid more (ask more in return)
when I have more free space

35. Effect of One Maverick Site
always bids high

36. Security & Privacy Issues: Anonymity Reputation Accountability
Information Preservation
Information Quality
Trust
Denial of service attacks

37. Information Preservation
Example Policy: make 3 copies of documents A1
make copies
What can go wrong?

38. A1 A1 A’1 What Can Go Wrong? “Bad” sites make copies
“Bad” site alters copy
“Bad” site publishes fake
“Bad” site makes may copies of other docs
... A1 A1
make copies
A’1

39. Conclusion P2P systems popular today
P2P systems vulnerable and inefficient
Many challenges ahead
Search
Resource Management
Security and Privacy

40. For Additional Information
Google: “Stanford Peers”