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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