1. Distributed Computing Systems CSCI 4780/6780

2. Geographical Scalability Challenges Synchronous communication –Waiting for a reply does not scale well!! Unreliable networks –Broadcasting does not work Centralized components –Will eventually become bottlenecks Multiple administrative domains –Security mechanisms do not come for free

3. Scalability Techniques Hiding communication latencies –Asynchronous communication –Reduce amount of data transmitted Distribution –Spreading work across system Caching and replication –Make copies of data and services Balance load –Avoid hot spots

4. Scaling Techniques 1.4 The difference between letting: a)a server or b)a client check forms as they are being filled

5. Scaling Techniques (2) 1.5 An example of dividing the DNS name space into zones.

6. Pitfalls Network is reliable Network is secure Network is homogeneous Topology does not change Latency is zero Bandwidth is infinite Transport cost is zero Single administrator

7. Types of Distributed Systems High-Performance Computing Systems Cluster computing Grid computing Distributed Information Systems Transaction processing systems Enterprise application integration P2P systems Distributed Pervasive Systems Mobile networks Sensor networks

8. Cluster Computing Super computing using PCs/workstations Used for parallel programming Homogeneity among nodes Master allocates nodes to tasks Compute nodes run standard operating systems (and may be a very thin middleware) Middleware consists of parallel programming libraries

9. Cluster Computing Systems An example of a cluster computing system.

10. Grid Computing Formed from heterogeneous set of machines May belong to different organizations Virtual organization Resource access and management 4-layered organization Fabric layer – Interfacing to local resources Connectivity layer – Connection handling and security Resource layer – Managing a single resource Collective layer – Simultaneous management of multiple resources Application layer – Hosts applications

11. Grid Computing Systems A layered architecture for grid computing systems.

12. Distributed Information Systems Lots of networked applications Sometimes belonging to different organizations Little interoperability Simplest integration Bundling operations together at client end Enterprise application integration Applications talking to each other

13. Transaction Processing Systems

14. Properties of Transactions Atomic: To the outside world, the transaction happens indivisibly. Consistent: The transaction does not violate system invariants. Isolated: Concurrent transactions do not interfere with each other. Durable: Once a transaction commits, the changes are permanent.

15. Examples Banking example Airline ticket booking example

16. Nested Transactions Transactions constructed from multiple sub- transactions Example: Travel Agent Problem with nested transactions What if one of the sub-transactions fail? TP monitor architecture

17. Nested Transactions

18. Transaction Processing Architecture The role of a TP monitor in distributed systems.

19. Enterprise Application Integration Middleware as a communication facilitator in enterprise application integration.

20. Distributed Pervasive Systems Ad hoc composition Extreme heterogeneity Wired network/wireless network High churn rate Resource constraints Contextual changes Possible mobility