[jira] [Commented] (OAK-9625) Support ordered index for first value of a multi-valued property, node name, and path

["Julian Reschke (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-9625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17573781#comment-17573781 ] 

Julian Reschke commented on OAK-9625:
-------------------------------------

[~thomasm] - I was wondering how to use this feature without knowing the details of the underlying JCR implementation. Maybe we could add a repostitory descriptor what will tell us whether it's supported? (Otherwise the only way I can think of is to check query results and detect at runtime whether the sorting actually worked).

> Support ordered index for first value of a multi-valued property, node name, and path
> -------------------------------------------------------------------------------------
>
>                 Key: OAK-9625
>                 URL: https://issues.apache.org/jira/browse/OAK-9625
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: indexing, lucene, query
>            Reporter: Thomas Mueller
>            Assignee: Thomas Mueller
>            Priority: Major
>             Fix For: 1.42.0
>
>
> Keyset pagination https://jackrabbit.apache.org/oak/docs/query/query-engine.html#Keyset_Pagination requires ordered indexing on a property. 
> If all we have is a property "x", which is set on "nt:base" (or a similar node type), then an ordered index on the property "x" can be used for pagination. However, if the property is sometimes multi-valued, then it's not possible, because we don't support ordered indexes on multi-valued properties.
> {noformat}
> /jcr:root//element(*, nt:base)
> [jcr:first(@alias) >= $lastEntry]
> order by jcr:first(@alias), @jcr:path
> /oak:index/aliasIndex
>   - type = lucene
>   - compatVersion = 2
>   - async = async
>   - includedPaths = [ "/" ]
>   - queryPaths = [ "/" ]
>   + indexRules
>     + nt:base
>       + properties
>         + firstAlias
>           - function = "first([alias])"
>           - propertyIndex = true
>           - ordered = true
> {noformat}
> If we have a property that is set on a mixin type (or primary node type), then the index can be much smaller, as we only need to index that node type. However, even here we need a property to do pagination. One option is to order by the lower case version of the name. However, this is quite strange. Also, the node name may not be unique, which complicates things further. It would be good if we can define an ordered index on the path itself (which is unique).
> {noformat}
> select [jcr:path], * from [nt:file]
> where path() >= $lastEntry
> and isdescendantnode(a, '/content')
> order by path()
> /oak:index/fileIndex
>   - type = lucene
>   - compatVersion = 2
>   - async = async
>   - includedPaths = [ "/content" ]
>   - queryPaths = [ "/content" ]
>   + indexRules
>     + nt:file
>       + properties
>         + path
>           - function = "path()"
>           - propertyIndex = true
>           - ordered = true
> {noformat}
> It would be good if ordering by node name would use the function index. Test case:
> {noformat}
> select [jcr:path], * from [nt:file] as a
> where name(a) >= $lastEntry
> and isdescendantnode(a, '/content')
> order by name(a), [jcr:path]
> /oak:index/fileIndex
>   - type = lucene
>   - compatVersion = 2
>   - async = async
>   - includedPaths = [ "/content" ]
>   - queryPaths = [ "/content" ]
>   + indexRules
>     + nt:file
>       + properties
>         + nodeName
>           - function = "name()"
>           - propertyIndex = true
>           - ordered = true
> {noformat}



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