Enhance task field for explain/explain analyze #33332
Description
Enhancement
Currently, the output of explain/explain analyze contains a column named task, it can be
- root: the task is running in TiDB
- cop[tiflash]: the task is runing in TiFlash via
CopRequest - cop[tikv]: the task is running in TiKV via
CopRequest - batchCop[tiflash]: the task is running in TiFlash via
BatchCopRequest
However, since v5.0.0, TiDB/TiFlash support mpp, that is some tasks are actually running in TiFlash via MPPRequest, but task in the output of explain does not support this, even if the task is running in mpp mode, it still shows cop[tiflash] or batchCop[tiflash], this will make user confused, better to add a new task type mpp[tiflash] to show that the task is running in TiFlash via MPPRequest