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https://issues.apache.org/jira/browse/OAK-1898?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14037208#comment-14037208
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Thomas Mueller commented on OAK-1898:
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It would be great if we had a very rough estimate on the number of child nodes
below a given path. 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.
See also OAK-894, where a mechanism is described to track descendent node
counts.
> Query: Incorrect cost calculation for traversal
> -----------------------------------------------
>
> Key: OAK-1898
> URL: https://issues.apache.org/jira/browse/OAK-1898
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: query
> Affects Versions: 1.0, 1.0.1
> Reporter: Thomas Mueller
> Assignee: Thomas Mueller
> Fix For: 1.1, 1.0.2
>
> Attachments: [OAK][TraversingIndex] Incorrect cost calculation_.pdf
>
>
> For queries of the following type, the estimated cost of traversal is very
> low if the number of path elements is high:
> {noformat}
> /jcr:root/path/with/many/elements/in/it//*
> {noformat}
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