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https://issues.apache.org/jira/browse/SOLR-8220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15067566#comment-15067566
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Erick Erickson commented on SOLR-8220:
--------------------------------------
WARNING: I'm stealing this code and back-porting to 4.x for my own purposes so
this may not pertain to 5x. And I'm not very up on the low-level details.
But this loop for reading multiValued fields puts _all_ the multivalued fields
for _all_ the docs on the shard into each doc:
{code}
if (values != null && DocValues.getDocsWithField(atomicReader,
fieldName).get(docid)) {
values.setDocument(docid);
if (values.getValueCount() > 0) {
List<Object> outValues = new LinkedList<Object>();
for (int i = 0; i < values.getValueCount(); i++) { // Iterates
more than just this doc, I think all of them!
{code}
I had more luck with
{code}
if (values != null) {
values.setDocument(docid);
List<Object> outValues = new LinkedList<Object>();
for (int ord = (int) values.nextOrd(); ord !=
SortedSetDocValues.NO_MORE_ORDS; ord = (int) values.nextOrd()) {
{code}
Note that I also think this is unnecessary in the if test, the loop above
doesn't do anything bad if there are docs with empty fields:
{code}
DocValues.getDocsWithField(atomicReader, fieldName).get(docid)
{code}
I changed it to just if (values != null). But I did have to test
outValues.size() > 0 before doing the addField after the loop or I got empty
braces in the output doc.
Again let me emphasize that
1> I don't know this code well, so take this with a grain of salt
2> I needed this for a one-off on the 4.x code line and this may work with 5x
just fine as-is. Needless to say what I'm doing will never make into the
official project....
But this saved me a TON of work, glad you're tackling this!
> 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-8220-5x.patch, SOLR-8220-ishan.patch,
> SOLR-8220-ishan.patch, SOLR-8220-ishan.patch, SOLR-8220-ishan.patch,
> SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch,
> SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch,
> SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch,
> SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch, SOLR-8220.patch,
> 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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