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Web Application Servers. Dean Jacobs BEA WebLogic. The Right Question. Middleware is converging Web Application Servers = TP Monitors What new demands do the Internet and Java place on middleware?. System Architecture. Database. Browsers. Web Servers. Application Server Cluster.
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Web Application Servers Dean Jacobs BEA WebLogic
The Right Question • Middleware is converging • Web Application Servers = TP Monitors • What new demands do the Internet and Java place on middleware?
System Architecture Database Browsers Web Servers Application Server Cluster
Web Servers • Web Servers not integrated with middleware • Adds an extra server-side hop with no benefit • Obviates the front line of session concentration • Web Servers integrated with middleware • Standard Web Servers must be supported • Front line session handling - load balancing and transactions - must occur in Web Server plug-ins
Relaxed Durability/Consistency • Trade durability or consistency for performance: avoid disk accesses by keeping state in memory. • Shopping Cart Stored as browser-session state in a servlet engine. To avoid writing backups to disk, replicate in-memory on a secondary host. • Catalog Data Changes infrequently and may be briefly out-of-date. To avoid disk reads, cache on many servers in a cluster. Update anywhere and lazily flush the caches.
Fat Processes with Threads • Radically different process model: 2-3 processes per host, each a logical machine • Multiple resource managers per process • Multiple threads accessing each resource • Threads are not isolated from each other
Object Lifetime In-Memory • CORBA relies on the programmer to release objects • Component models (EJB) prescribe object lifetimes • Programming language object models (RMI) require DGC. How can that scale?