[jira] [Created] (OAK-9522) Index cost estimation: prefer union query with path restriction

["Thomas Mueller (Jira)" <ji...@apache.org>]

Thomas Mueller created OAK-9522:
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             Summary: Index cost estimation: prefer union query with path restriction
                 Key: OAK-9522
                 URL: https://issues.apache.org/jira/browse/OAK-9522
             Project: Jackrabbit Oak
          Issue Type: Improvement
            Reporter: Thomas Mueller


If there is a query of this form with an index that supports path restrictions (evaluatePathRestrictions = true):
{noformat}
select * from [nt:base] where [indexedProperty] = x 
and (issamenode('/content') or isdescendantnode('/content'))
{noformat}
then the path restriction isn't used in the index.
This is unfortunate, because the index returns a lot more results, and the query engine will have to check if the path matches the condition.

How this works: the query engine creates two possible queries:
* plan a: one with just the [indexedProperty] = x condition, and no path restriction
* plan b: a union query, where one side uses issamenode and the other side uses isdescendantnode.

The index will return the same cost no matter if a path condition is there or not. And that's why the query engine will pick plan a: because the cost of the union query is higher.

The index should return a lower cost if there is a path restriction. (Right now the query engine will reduce the cost if there is a path restriction, but that's not sufficient for this case).





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