[jira] [Commented] (SOLR-15440) contrib/ltr FieldValueFeature: DocValues use for stored fields

["Christine Poerschke (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-15440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17352391#comment-17352391 ] 

Christine Poerschke commented on SOLR-15440:
--------------------------------------------

Sketched out below is one way this could be done in terms of code. It's a code fragment sketch only i.e. test coverage and documentation updates in javadoc/CHANGES.txt/Solr Ref Guide/etc. would of course all also be required especially since it's a not backwards compatible change.
{code:java}
public class FieldValueFeature extends Feature {

+ @Deprecated
+ final private boolean useDocValuesForStored;

  public FieldValueFeature(String name, Map<String,Object> params) {
    super(name, params);
+   this.useDocValuesForStored = true;
  }

+ @Deprecated
+ protected FieldValueFeature(String name, Map<String,Object> params, boolean useDocValuesForStored) {
+   super(name, params);
+   this.useDocValuesForStored = useDocValuesForStored;
+ }

  ...
    public FeatureScorer scorer(LeafReaderContext context) throws IOException {
      if (schemaField != null &&
-         !schemaField.stored() &&
+         (!schemaField.stored() || useDocValuesForStored) &&
          schemaField.hasDocValues()) {
      ...
    }
  ...

}

@Deprecated // will be removed in Solr 9.X or Solr 10
final public class LegacyFieldValueFeature extends FieldValueFeature {

  public LegacyFieldValueFeature(String name, Map<String,Object> params) {
    super(name, params, false /* useDocValuesForStored */);
  }

}
{code}

> contrib/ltr FieldValueFeature: DocValues use for stored fields
> --------------------------------------------------------------
>
>                 Key: SOLR-15440
>                 URL: https://issues.apache.org/jira/browse/SOLR-15440
>             Project: Solr
>          Issue Type: Improvement
>          Components: contrib - LTR
>            Reporter: Christine Poerschke
>            Priority: Major
>
> SOLR-12697 in Solr 8.9 is intending to add {{FieldValueFeature}} support "stored=false docValues=true" a.k.a. pure DocValues fields.
> The SOLR-12697 changes are implemented in a backwards compatible manner i.e. existing behaviour for "stored=trued docValues=true" a.k.a. stored DocValues fields does not change.
> This ticket here is to explore how backwards compatibility could potentially be broken (in a safe manner) in future e.g.
>  * Solr 9.0 breaks backwards compatibility for {{FieldValueFeature}} but provides a deprecated {{LegacyFieldValueFeature}} with the existing behaviour for users who need that.
>  * Solr 9.X or 10.0 removes the deprecated {{LegacyFieldValueFeature}} class and users still needing the legacy behaviour need to create and maintain an equivalent local custom class.



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