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https://issues.apache.org/jira/browse/LUCENE-8996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16972240#comment-16972240
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Christine Poerschke commented on LUCENE-8996:
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bq. ... can I patch on top of your patch?
Sure, please go ahead.
I'm sorry I've had only very limited time recently here and elsewhere. I'll
unassign the ticket to try and make it clearer that it's fully up-for-grabs.
> 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
> Attachments: LUCENE-8996.02.patch, LUCENE-8996.03.patch,
> LUCENE-8996.04.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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