[jira] [Created] (CALCITE-4392) The operation of checking types equal ignoring null can be more efficient

["Liya Fan (Jira)" <ji...@apache.org>]

Liya Fan created CALCITE-4392:
---------------------------------

             Summary: The operation of checking types equal ignoring null can be more efficient
                 Key: CALCITE-4392
                 URL: https://issues.apache.org/jira/browse/CALCITE-4392
             Project: Calcite
          Issue Type: Improvement
          Components: core
            Reporter: Liya Fan
            Assignee: Liya Fan


Method {{SqlTypeUtil#equalSansNullability(RelDataTypeFactory, RelDataType, RelDataType) is on the hot path for many scenarios, as it compare types with nullability ignored.

In the implementation, the expensive operations are {{RelDataType#equals(Object)}} and {{RelDataTypeFactory#createTypeWithNullability}}, especially for types with multiple sub-fields. 

For the current implementation, the {{RelDataType#equals(Object)}} is called at least once, and {{RelDataTypeFactory#createTypeWithNullability}} is called whenever the nullability values are different. 

We can improve the implementation so that {{RelDataType#equals(Object)}} is called at most once, and the call to {{RelDataTypeFactory#createTypeWithNullability}} can be avoided if the types are totally different (with different type names, and nullability values)

{{noformat}}
if (type1.isNullable() == type2.isNullable()) {
  return type1.equals(type2);
} else {
  return type1.equals(
        factory.createTypeWithNullability(type2, type1.isNullable()));
}
{{noformat}}



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