Thomas Mueller created OAK-1907:
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Summary: Better cost estimates for traversal, property, and
ordered indexes
Key: OAK-1907
URL: https://issues.apache.org/jira/browse/OAK-1907
Project: Jackrabbit Oak
Issue Type: Improvement
Components: query
Affects Versions: 1.0, 1.0.1, 1.0.2
Reporter: Thomas Mueller
Assignee: Thomas Mueller
Fix For: 1.1
Currently, cost estimates of traversal, property index, and ordered index don't
take the number of nodes into account, if there are more than about 100 nodes.
This is problematic because in many cases, the wrong index is used (because of
incorrect cost estimate).
To get a better estimate, a very rough estimate on the number of child nodes
below a given path is needed.
One idea is: when adding a node, if Math.random() < 0.00001, add a hidden,
randomly named property (for example called ":count-xyz" where xyz is a uuid,
value 100'000) to the parents of that node, so that we know there are probably
more than 100'000 nodes below a given path. When removing a node, with the same
algorithm add a hidden property (":count-xyz", value -100'000). That should
result in a slowdown of less than 0.01%, but should allow us much better cost
estimates. Those properties could be consolidated asynchronously if needed.
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