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https://issues.apache.org/jira/browse/LUCENE-8996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16958037#comment-16958037
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Christine Poerschke commented on LUCENE-8996:
---------------------------------------------
Investigating this further and confidently coming up with an alternative fix
would likely hold up the 8.3.0 release process.
Any and all input and help appreciated, as always.
In the meantime I'll proceed to revert the commits above so as to avoid
delaying the release process. Version control is (sometimes at least) meant for
that, right? Sorry about the noise.
> maxScore is sometimes missing from distributed grouped responses
> ----------------------------------------------------------------
>
> Key: LUCENE-8996
> URL: https://issues.apache.org/jira/browse/LUCENE-8996
> Project: Lucene - Core
> Issue Type: Bug
> Affects Versions: 5.3
> Reporter: Julien Massenet
> Assignee: Christine Poerschke
> Priority: Minor
> Fix For: master (9.0), 8.3
>
> Attachments: LUCENE-8996.02.patch, LUCENE-8996.patch,
> LUCENE-8996.patch, lucene_6_5-GroupingMaxScore.patch,
> lucene_solr_5_3-GroupingMaxScore.patch, master-GroupingMaxScore.patch
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> This issue occurs when using the grouping feature in distributed mode and
> sorting by score.
> Each group's {{docList}} in the response is supposed to contain a
> {{maxScore}} entry that hold the maximum score for that group. Using the
> current releases, it sometimes happens that this piece of information is not
> included:
> {code}
> {
> "responseHeader": {
> "status": 0,
> "QTime": 42,
> "params": {
> "sort": "score desc",
> "fl": "id,score",
> "q": "_text_:\"72\"",
> "group.limit": "2",
> "group.field": "group2",
> "group.sort": "score desc",
> "group": "true",
> "wt": "json",
> "fq": "group2:72 OR group2:45"
> }
> },
> "grouped": {
> "group2": {
> "matches": 567,
> "groups": [
> {
> "groupValue": 72,
> "doclist": {
> "numFound": 562,
> "start": 0,
> "maxScore": 2.0378063,
> "docs": [
> {
> "id": "29!26551",
> "score": 2.0378063
> },
> {
> "id": "78!11462",
> "score": 2.0298104
> }
> ]
> }
> },
> {
> "groupValue": 45,
> "doclist": {
> "numFound": 5,
> "start": 0,
> "docs": [
> {
> "id": "72!8569",
> "score": 1.8988966
> },
> {
> "id": "72!14075",
> "score": 1.5191172
> }
> ]
> }
> }
> ]
> }
> }
> }
> {code}
> Looking into the issue, it comes from the fact that if a shard does not
> contain a document from that group, trying to merge its {{maxScore}} with
> real {{maxScore}} entries from other shards is invalid (it results in NaN).
> I'm attaching a patch containing a fix.
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