Backup Stage in query plan

[Edson Ramiro <er...@gmail.com>]

Hi all,

I found in the explain a "backup stage", but I didn't find any docs
explaining what it is.

What is a "backup stage"? Do you have any doc about it?

I got this from the `explain formatted' of the TPCH 16 query.

 "STAGE DEPENDENCIES": {
    "Stage-9": {
      "DEPENDENT STAGES": "Stage-3, Stage-6"
    },
    "Stage-8": {
      "ROOT STAGE": "TRUE",
      "CONDITIONAL CHILD TASKS": "Stage-10, Stage-3"
    },
    "Stage-2": {
      "DEPENDENT STAGES": "Stage-0"
    },
    "Stage-0": {
      "DEPENDENT STAGES": "Stage-5"
    },
    "Stage-6": {
      "DEPENDENT STAGES": "Stage-10"
    },
    "Stage-10": {
      "BACKUP STAGE": "Stage-3"
    },
    "Stage-5": {
      "DEPENDENT STAGES": "Stage-9"
    },
    "Stage-3": {}
  }

Thanks in advance,

      Edson Ramiro