1. Competitive algorithms for the dynamic selection of component implementations D M Yellin

2. Mix-n-match Many current apps built by integrating existing components Java Beans and Web services Component programming models = component based development However, all is not well Performance is not optimized Association is loose (different vendors etc)

3. The problem The adaptive component problem Heavy costs to switch Algorithm needed at run time Applicability to 2 problems Pub/sub – loosely related components read/write shared db Data structure selection – best way for representation for faster access?

4. Delta Algorithm 2 choice algorithm – assumes that there are two valid choices for each situation Given that impl. is active, it scans the requests, and looks at the costs of that. If the alternative implementation is lower, change impl. Overly simplistic? Bursty traffic?

5. What Delta should do Based on current workloads Obtained by monitoring Switch models adaptively when needed Hence optimize the workload

6. Example: The pub/sub problem Pub/sub problem: Database with many accessing nodes Writes goto server, caches on read Application by monitoring each client Switch to sub mode when cost is lower than nonsub mode

7. How does client know about writes peformed by other clients? No increase in traffic Piggyback write data counts on transmissions Still more data

8. Adapative Component Problem Requests can be catergorized into using key 1 and key 2 Delta can be used to convert this into impl using key 1 and key 2, and switching between them dynamically Alternative: 2 index tables implemented as dictionary – not always feasible (res overheads)

9. Competitiveness Apparently this is to justify the existance of Delta Theorem 1: Algorithm Delta is (3+ e)- competitive for any two-implementation- component problem (Proof. Lots of it)

10. Limitations Only can choose from two components Is there an algorithm for choosing from arbitrary number of impls? One shot switch required Expensive! Better: switch incrementally Competitiveness only Other models can be considered Periodical activity can be used as metric instead?

11. Comments? Too much math involved. No real examples (framework only) Very dry