1. A Scalable Service Architecture for Distributed Search Mark Jessop University of York

2. Distributed Aircraft Maintenance Environment - DAME The Search Problem DAME demonstrated Grid for distributed decision support in maintenance environments: Rolls-Royce Core element is searching large distributed datasets ‘Query by Content’ approach is used to find similar vibration patterns to observed engine anomalies

3. Distributed Aircraft Maintenance Environment - DAME Service Architecture Large datasets and small query – move processing to the data Service stack: Web Services, Native apps, data management service Tracked Orders SRB Catalogue Services Pattern Match Control Data Extractor Pattern Match Engines Global MCAT Signal Data Explorer PMC: Front end manages search requests PMS: Performs pattern matching SRB: Gives virtualised view of data All services only work at local level

4. Distributed Aircraft Maintenance Environment - DAME Evaluation Aim was to be efficient and scalable in distributed search Performance evaluation of the architecture was required for verification Three implementation compared: –Java/OGSA web services –C++ (gSOAP) web services –Native sockets (C++) How many nodes can architecture support?

5. Distributed Aircraft Maintenance Environment - DAME Modelling the System Assumptions: –Each node is of the same specification –Pattern matching algorithm is fully parallel –Every node is equal distance from the master –Clients ask for no more than 100 results Investigates performance of a single search T = time, w = work, n = number of nodes, o = serial part of overhead, c = parallel part of overhead

6. Distributed Aircraft Maintenance Environment - DAME Measuring the System Performance increases as nodes are added… …until the optimum number of nodes is reached The larger the work load, the more nodes can be added and still maintain efficiency The serial overhead governs efficiency and scalability Experiments aim to measure this overhead

7. Distributed Aircraft Maintenance Environment - DAME Performance… Nodes running at Sheffield, Leeds and York Measured invocation times from Sheffield and Leeds to York. Each measurement recorded three search invocations at a time for each implementation, repeated throughout the day Recorded raw performance, no security infrastructure

8. Distributed Aircraft Maintenance Environment - DAME …Performance

9. Distributed Aircraft Maintenance Environment - DAME Hierarchical Organisation… Current model the overhead is proportional to the number of nodes A hierarchy allows concurrency in delivering requests and merging results Search time complexity could be reduced from w/n+n to w/n+log n Increases management complexity Assuming structure doesn’t add overhead

10. Distributed Aircraft Maintenance Environment - DAME …Hierarchical Organisation

11. Distributed Aircraft Maintenance Environment - DAME Conclusions Use of Grid Services in Java restricts performance and scalability C++ services and raw sockets are similar in performance Hierarchical organisation could significantly improve performance