Specifications

Requirements

ViewsFlash is a standard Java Web Application that runs on any platform that supports the Servlet v2.3 specification. The ViewsFlash JSR168 compatible Survey Portlet requires a JSR168 certified portal.

Hardware Requirements
A server with a contemporary CPU, 1G RAM and 10GB of disk storage will provide sufficient capacity for most installations. CPU, RAM, and database power are the limiting components. Cluster configurations are recommended for scalability and availability.

Performance Considerations

ViewsFlash is designed from the ground up for maximum reliability and performance. It is written as a thread-safe, multithreaded servlet. For performance, computations are carried out entirely in main memory. All HTML is composed in main memory as well, and the connection to the visitor's browser maintains a keep-alive connection.

One main factor affecting performance is CPU speed and availability. On a single-processor 333 MHz Pentium-II PC (c.1998), using Tomcat and Oracle 8, and allocating 256M of RAM to the VM running web applications, ViewsFlash runs consistently, without memory leaks, at 30 page views per second, or 33 ms. turnaround time, including the time required to send all information back to the client browser, on a 10 megabit local area network. CPU utilization averaged 80%.

The other main factor affecting performance is database latency and availability. ViewsFlash caches data in RAM whenever possible, minimizing database access. Slow networks, insufficient database connections, and overworked databases can slow ViewsFlash performance significantly.

For heavy usage, the questionnaires in the intended application should be profiled using a stress testing tool to make sure that all components in the cluster scale to the expected volume.

For complete information on scalability, refer to Architecture.

Servlet Session Usage

ViewsFlash uses servlet sessions in these circumstances:
- to guarantee that during survey and poll design using the administrative UI, multiple page transactions (such as adding a question) are routed to the same servlet instance in a distributed environment.
- when requested explicitly in the Security page to identify respondents in multiple-page surveys.
- in JSR-168 portlets for caching.

Files Used

When not using a database, ViewsFlash writes all files to the "data" directory specified at installation time in the servlet parameters. Backing up this directory periodically will ensure against data loss. If the ViewsFlash data is being stored in a database, only those files marked * are kept in this directory.

Next: Staging