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https://issues.apache.org/jira/browse/SOLR-8220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15006669#comment-15006669
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Yonik Seeley commented on SOLR-8220:
------------------------------------
{quote}
2) There is no metadata (that I can find) stored for each document that says
whether it has an unstored docValue field, so efficiently loading docValues
fields based on FL=* would be difficult.
{quote}
In SolrIndexSearcher there is
{code}
private final FieldInfos fieldInfos;
private final Collection<String> fieldNames;
{code}
That gives you the full set of fields actually in-use by the index. Useful for
dealing with dynamicFields, where the names aren't explicitly listed in the
schema.
In the future, perhaps we should have some meta-data about what fields each
document contains.
> Read field from docValues for non stored fields
> -----------------------------------------------
>
> Key: SOLR-8220
> URL: https://issues.apache.org/jira/browse/SOLR-8220
> Project: Solr
> Issue Type: Improvement
> Reporter: Keith Laban
> Attachments: SOLR-8220.patch, SOLR-8220.patch
>
>
> Many times a value will be both stored="true" and docValues="true" which
> requires redundant data to be stored on disk. Since reading from docValues is
> both efficient and a common practice (facets, analytics, streaming, etc),
> reading values from docValues when a stored version of the field does not
> exist would be a valuable disk usage optimization.
> The only caveat with this that I can see would be for multiValued fields as
> they would always be returned sorted in the docValues approach. I believe
> this is a fair compromise.
> I've done a rough implementation for this as a field transform, but I think
> it should live closer to where stored fields are loaded in the
> SolrIndexSearcher.
> Two open questions/observations:
> 1) There doesn't seem to be a standard way to read values for docValues,
> facets, analytics, streaming, etc, all seem to be doing their own ways,
> perhaps some of this logic should be centralized.
> 2) What will the API behavior be? (Below is my proposed implementation)
> Parameters for fl:
> - fl="docValueField"
> -- return field from docValue if the field is not stored and in docValues,
> if the field is stored return it from stored fields
> - fl="*"
> -- return only stored fields
> - fl="+"
> -- return stored fields and docValue fields
> 2a - would be easiest implementation and might be sufficient for a first
> pass. 2b - is current behavior
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