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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

Web Application Servers

Dean Jacobs

BEA WebLogic


The right question
The Right Question

  • Middleware is converging

    • Web Application Servers = TP Monitors

  • What new demands do the Internet and Java place on middleware?


System architecture
System Architecture

Database

Browsers

Web Servers

Application Server Cluster


Web servers
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
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    • Catalog Data Changes infrequently and may be briefly out-of-date.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
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
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?


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