Is there a way to globally turn off new caching feature. Useful when debugging.

Not built-in. Out of my head, I can think of these options:

A. Manage your own AppSetting on your config and check for it when creating your QueryParameters:

// register caching
CacheController.RegisterCache(string.Empty, new ResultsetCache());

// determine globally whether or not to use caching
var cachingEnabled = GetCachingEnabledFlagFromConfig();
            
var customers = new EntityCollection<CustomerEntity>();         
using (var adapter = new DataAccessAdapter())
{
    var parameters = new QueryParameters()
    {
        CollectionToFetch = customers,
        FilterToUse = CustomerFields.Country == "USA",
        CacheResultset = cachingEnabled,
        CacheDuration = new TimeSpan(0, 0, 10)  // cache for 10 seconds
    };
    adapter.FetchEntityCollection(parameters);
}

B. Create your own version of ResultsetCache that checks for that AppSeting (see A), so it knows whether or not to turn on/off _purgeTimer.Enabled at the ctor.

Didn't think of that scenario, would be a useful addition, though David's workaround might also work till the switch is added in a future version

I think I'll just do .CacheResultset(TimeSpan.FromMinutes(x)) where x is going to be 0 when debugging for the time being (using LINQ to LLBLGenPro). But thanks for the other options.

Or even easier, when debugging, don't RegisterCache at all.