Syntax: comma-separated list of query variable names
If set, the Search Appliance will remove all but the these query variables when walking URLs. This can be useful when you know only a few select query variables are important, and others may appear but are irrelevant.
All the named variables are not required to be present, they are simply the ones that will be let through.
For example, setting Keep Query Vars to
id,type will turn the URL