Query behaviour when you cross the LowMemoryLimit

Here’s something that had me stumped for quite a long time earlier this week…

I’m doing some performance tuning work for a customer at the moment, and following my usual approach I took a test query, cleared the cache, ran it and noted how long it ran for and what I saw in Profiler and MDX Studio. However this time I saw some strange things happening: I’d run the same query on a cold cache more than once and the query times would differ by anything up to a minute; even more confusing, the information I got from Profiler and MDX Studio would be different too – for example, the number of Query Subcube Verbose events in recorded in Profiler for a query might differ from run to run by several hundred. This had me completely confused. There was no-one else on the server and I was running on a cold cache. What was going on?