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Posted to issues@lucene.apache.org by "Christine Poerschke (Jira)" <ji...@apache.org> on 2019/10/01 16:23:00 UTC
[jira] [Commented] (LUCENE-8996) maxScore is sometimes missing from
distributed grouped responses
[ https://issues.apache.org/jira/browse/LUCENE-8996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16942115#comment-16942115 ]
Christine Poerschke commented on LUCENE-8996:
---------------------------------------------
Looking at the {{master-GroupingMaxScore.patch}} patch and the [https://github.com/apache/lucene-solr/pull/906] pull request I'm wondering if backwards compatibility considerations apply w.r.t. the initialisation of the {{maxScore}} and {{totalMaxScore}} local variables?
Attached LUCENE-8996.patch tries to illustrate what I mean; it also adds javadocs for the "not-NaN max" helper method (but contains neither the patch's nor the pull request's tests, temporarily to make it (perhaps) easier to focus on the code change).
Haven't looked too closely though yet i.e. it could be that whatever value is used to initialise those local variables never makes it "out of the method" or it never makes it into "client visibility" in which case the initial value of the local variable would be just implementation detail (with NaN likely the clearer choice).
> 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
> Priority: Minor
> Attachments: 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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