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