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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?
Browsers
Database
Web ServersApplication Server
Cluster
System Architecture
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• Catalog Data Changes infrequently and may be briefly out-of-date.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?