[jira] [Created] (CALCITE-4212) Revisit cost-model to break ties between Enumerable and Bindable expressions

["Stamatis Zampetakis (Jira)" <ji...@apache.org>]

Stamatis Zampetakis created CALCITE-4212:
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             Summary: Revisit cost-model to break ties between Enumerable and Bindable expressions
                 Key: CALCITE-4212
                 URL: https://issues.apache.org/jira/browse/CALCITE-4212
             Project: Calcite
          Issue Type: Improvement
            Reporter: Stamatis Zampetakis


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}}

{code:sql}
select "product_name", 0 as zero
from "foodmart"
order by "product_name";
{code}

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

+Choice 1+
{noformat}
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
{noformat}

+Choice 2+
{noformat}
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
{noformat}

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. 



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