[jira] [Commented] (OAK-2730) Faster result count estimation for QueryResult on lines of resultFetchSize support in JR2

["Chetan Mehrotra (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-2730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14484843#comment-14484843 ] 

Chetan Mehrotra commented on OAK-2730:
--------------------------------------

Such a support can be left to index implementation as it would be easier to provide such a support with Lucene based implementation and might not be easy to support with PropertyIndex. An index implementation can expose this capability as part of plan and QE can then make use of that via some new API. {{resultFetchSize}} can be configured as part of {{QueryEngineSettings}}

> Faster result count estimation for QueryResult on lines of resultFetchSize support in JR2
> -----------------------------------------------------------------------------------------
>
>                 Key: OAK-2730
>                 URL: https://issues.apache.org/jira/browse/OAK-2730
>             Project: Jackrabbit Oak
>          Issue Type: New Feature
>          Components: query
>            Reporter: Chetan Mehrotra
>             Fix For: 1.3.0
>
>
> Currently in Oak while fetching the result size for a query the time taken is proportional to the result size. This would not perform well when result size is big. The complete traversal is required to perform ACL check to ensure that result count is *accurate*
> JR2 used to support {{resultFetchSize}} (default to integer max).  This was used to get an estimate of possible result count whereby the count might not be accurate.
> Per [~mreutegg] this feature worked like below
> {quote}
> If resultFetchSize is set to 50 then QueryEngine will initially collect up to 50 nodes the current session is allowed to read from the raw lucene result set. While doing that, it counts the number of nodes denied by access control checks. The result size reported is then calculated as: raw-lucene-result-size - number-of-nodes-denied. The resultFetchSize is double and the query executed again if a client iterates passed the currently available nodes. If it is required to have an exact result size, then the configuration for 'resultFetchSize' can be increased to a much higher value. However, this has a severe performance impact for large result sets, because the query will now have to apply access control checks for the complete result set
> {quote}



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