Chetan Mehrotra created OAK-2730:
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Summary: 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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