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https://issues.apache.org/jira/browse/LUCENE-8996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16958814#comment-16958814
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Diego Ceccarelli commented on LUCENE-8996:
------------------------------------------
Interesting - I'm curious to dig into why the distribute query returned
{{maxScores==Float.MIN}} given that with [~cpoerschke] we thought very rare to
happen.
It seems that the query that produced the failure:
{code:java}
... webapp= path=/select
params={q=*:*&shards=http://127.0.0.1:62435/collection1|[ff01::213]:33332/|[ff01::114]:33332/|[ff01::083]:33332/&fl=id,a_i1&group.limit=-1&sort=a_i1+asc,+id+asc&rows=100&wt=javabin&version=2&group.field=a_i1&group=true}
status=0 QTime=10
[junit4] 2> 2169480 ERROR
(TEST-TestDistributedGrouping.test-seed#[9532D3AC873FA0D8]) [ ]
o.a.s.BaseDistributedSearchTestCase Mismatched responses:
{code}
.. was a MatchAll {{*:*}} + sort - I'm wondering if this particular combination
produces some particular effect on the computation of MaxScore, I'm going to
play with the unit tests.
> 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.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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