If the blocking plan used by the CachedPlanStage fails during execution and falling back to the backup plan is required, the following should be written to QLOG:

• A message indicating that the backup plan is being switched to.
• The current execution stats for the blocking plan.
• The error message corresponding to the failure of the blocking plan, if an error message is available.

Currently, the CachedPlanStage does no logging when switching to the backup plan.