The join cost model requires the WT cache size as an input. This value is based on the physical RAM size, server parameters and other factors. In the initial implementation, we invoked WiredTigerUtil::collectConnectionStatistics(), which is what serverStatus() uses. This performs a lot more work than what is necessary for the optimizer.

This ticket represents the work to expose a helper which performs just the amount of work necessary to query WT for the cache size. It may also be necessary to cache this value (only compute it on startup and server parameter changes).