Uploaded image for project: 'Calcite'
  1. Calcite
  2. CALCITE-4212

Revisit cost-model to break ties between Enumerable and Bindable expressions

    XMLWordPrintableJSON

Details

    • Improvement
    • Status: Open
    • Major
    • Resolution: Unresolved
    • None
    • None
    • None
    • None

    Description

      Most Enumerable and Bindable expressions use exactly the same cost function to compute cost. Depending on the query this may lead to different equivalent (sub) plans with exactly the same cost. This makes the plans dependent on the order that the rules are applied.

      Let's consider for example the following query present in DruidAdapterIT#testProject

      select "product_name", 0 as zero
      from "foodmart"
      order by "product_name";
      

      At some point during planning the optimizer needs to decide between the following plans:

      Choice 1

      EnumerableSort(sort0=[$0], dir0=[ASC]), id = 37
        EnumerableInterpreter(subset=[rel#23:RelSubset#1.ENUMERABLE.[]]), id = 43
          DruidQuery(subset=[rel#26:RelSubset#1.BINDABLE.[]], table=[[foodmart, foodmart]], intervals=[[1900-01-09T00:00:00.000Z/2992-01-10T00:00:00.000Z]], projects=[[$3, 0]]), id = 25
      

      Choice 2

      EnumerableInterpreter, id = 61
        BindableSort(subset=[rel#40:RelSubset#1.BINDABLE.[0]], sort0=[$0], dir0=[ASC]), id = 41
          DruidQuery(subset=[rel#26:RelSubset#1.BINDABLE.[]], table=[[foodmart, foodmart]], intervals=[[1900-01-09T00:00:00.000Z/2992-01-10T00:00:00.000Z]], projects=[[$3, 0]]), id = 25
      

      Both choices have exactly the same cost since BindableSort and EnumerableSort use the same cost function (Sort#computeSelfCost, RelMdRowCount#getRowCount(Sort, RelMetadataQuery)).

      The issue can appear with various other expressions such as Project, SetOp, etc.

      Although the example is taken from the Druid adapter the same can happen if both Bindable and Enumerable conventions are used during planning in other use-cases.

      Attachments

        Issue Links

          Activity

            People

              Unassigned Unassigned
              zabetak Stamatis Zampetakis
              Votes:
              0 Vote for this issue
              Watchers:
              2 Start watching this issue

              Dates

                Created:
                Updated: