The current default wired tiger session_max limit is 20k. Unfortunately, this can often put session creation as the first terminal failure when adding many live connections.

Since we currently use a thread per connection, and the vast majority of users don't alter pid_max, pushing the limit up to 33k is likely to make thread exhaustion the first limit users hit, instead of the wt session limit. Thread exhaustion has slightly nicer semantics in that failure to create threads for ingress connection handling is non-terminal.