Adrien Grand created LUCENE-9003:
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Summary: Should FilterDirectoryReader compute numDocs lazily?
Key: LUCENE-9003
URL: https://issues.apache.org/jira/browse/LUCENE-9003
Project: Lucene - Core
Issue Type: Improvement
Reporter: Adrien Grand
FilterDirectoryReader extends BaseCompositeReader, which computes both maxDoc
and numDocs eagerly in its constructor by summing up these values across all
sub leaves.
This is problematic for readers that hide additional documents. Computing
numDocs on such leaf readers usually requires iterating over all live documents
to count them. This makes creating a FilterDirectoryReader on top run in linear
time, which has caused several performance bugs to us over time. This is
especially frustrating given that numDocs is a rarely used index statistic.
I think computing numDocs lazily would be less surprising?
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