Making the max concurrent query parameter configurable

By the original design, Columnstore allows only 10 concurrent MySQL queries. Additional queries are placed in a queue and to be processed on a first-come-first-served basis. This max queries mechanism was put in place because of memory requirement on the UM(s) for hashing joins. Evidently, it is not good for all hardware configurations, especially for hardware configurations that provide high CPU power and large memory. When disk-join is enabled, this restriction becomes less relevant.

I believe this max value of 10 is not configurable in Columnstore. I suggest that we change this hard-coded value to a configurable parameter in Calpont.xml. By default, it should be set to 0 for no limit. It can be set by the user when the throttling is required for the user’s environment. It should still be independent from the disk-join setting.