In clustered installations where you have created additional interviewer session engines, you can configure Phone Participants to use multiple interviewer session engines. This improves performance by allowing the activity to allocate interviewers to the least loaded engine and provides a recovery facility should an engine fail while interviews are in progress.

All telephone interviewing sessions have access to the default session engine (usually [INSTALL_FOLDER]\IBM\SPSS\DataCollection\<version>\Interviewer Server\\Server\mrIEngWS\mrIEngWS.dll) and to any other interviewer session engines named in the activity's Web.config file. To name alternate engines, put this definition in the <appSettings> section of the activity's Web.config file:

where engine_names is a comma-separated list of the URLs of interview engines. For example:

Each URL must be no more than 255 characters long.

When an interviewer starts Phone Participants, the activity reads the list of alternate interviewer session engines it may use and then runs the PercentLoaded method on the default engine and on the alternate session engines named in this file. It then allocates the interviewer to the least loaded engine, and all the interviews that the interviewer carries out will run using that engine.

The only time that Phone Participants switches to a different engine is if the current engine becomes unavailable. If an engine stops responding, Phone Participants goes through the list of session engines again, rechecking PercentLoaded (failed engines are not removed from the list of alternate engines), and selects the engine that now has the lowest loading figure. All the interviewer's interviews from now on will take place on the newly selected engine even if the old one becomes available again. When an interview session fails over in this way, Phone Participants creates an interviewer session, gets the appropriate sample record, and then restarts the interview. The interviewer is not normally aware of this background activity, but you'll find a record of these actions in the CIV*.log file.