[jira] [Updated] (OAK-7379) Lucene Index: per-column selectivity, assume 5 unique entries

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

     [ https://issues.apache.org/jira/browse/OAK-7379?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Julian Reschke updated OAK-7379:
--------------------------------
    Fix Version/s: 1.9.0

> Lucene Index: per-column selectivity, assume 5 unique entries
> -------------------------------------------------------------
>
>                 Key: OAK-7379
>                 URL: https://issues.apache.org/jira/browse/OAK-7379
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: lucene, query
>            Reporter: Thomas Mueller
>            Assignee: Thomas Mueller
>            Priority: Major
>              Labels: candidate_oak_1_8
>             Fix For: 1.9.0, 1.10
>
>
> Currently, if a query has a property restriction of the form "property = x", and the property is indexed in a Lucene property index, the estimated cost is the index is the number of documents indexed for that property. This is a very conservative estimate, it means all documents have the same value. So the cost is relatively high for that index.
> In almost all cases, there are many distinct values for a property. Rarely there are few values, or a skewed distribution where one value contains most documents. But in almost all cases there are more than 5 distinct values.
> I think it makes sense to use 5 as the default value. It is still conservative (cost of the index is high), but much better than now.



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