Scalability Factors

Alexander Wolf

John Mathon

Session Goals

Dimensions of Scale Metrics for Dimensions Gaining Confidence in Scalability Things to Do, Things to Avoid

Numbers, Numbers, and More Numbers

January 1998 Network Wizards Survey– 29,669,611 hosts in DNS

– 5,331,640 of these reply to ping

– 204 active level 1 domains

– 781,602 level 2 domains

– 10,380,858 level 3 domains

10^12 messages in stock market domain 10^10 phone calls for average of 3 min each 20,000 events per second

Internet Scale vs. Scalability

Can we characterize what we mean by “Internet Scale”?

Can we define/build an ISEN service that scales (up or down)?

Examples of Scale

News (but not really “event notification”) WWW (but essentially read only) DNS (but inherent structure) Telephony (but special purpose)

Issue: Internet vs. Wide Area

Metrics of Scale

Number of objects of interests Number of observers Number of interested parties Data storage and queuing Number/freq/dist of events Number/freq/dist of notifications Behavior of parties and objects

Achieving Scalability

What are the starting points for scale? How far can the system be stretched?

No systems acknowledged to be truly (infinitely) scalable

To how many orders of magnitude do we design a system to scale?

It is difficult ahead of time to know the growth parameters

Dealing with Scale

Where is the cost borne? What is the economic model? What are the requirements/scale of different

classes of applications?

Implementation Discussion

Tree vs. general graph structure of servers Is there a structure to subjects to optimize

routing and filtering? Is content-based addressing a requirement? All systems may be scalable with sufficient

expenditure of money

Things that Affect Scalability

Granularity– message size

Reliability of notification Latency / Quality of Service Collateral transactions resulting from events

Elvin Inquest

20,000 events a second Content-based addressing at an Internet scale is

feasible Mesh topology routing Not yet tested to Internet scale Subscriber is the next hop Not sure if linear with the number of leaves

Gaining Confidence in Scalability

Lack of data to parameterize simulation models Assertion: simulation won’t be useful

John Mathon will publish his “guesses” (based on TIBCO experience)