[LUCENE-2345] Make it possible to subclass SegmentReader

• Type: Wish
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Fix Version/s: 4.9, 6.0
• Component/s: core/index
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Tim Smith
• Created: 24/Mar/10 18:39
• Updated: 28/Aug/22 12:23

Description

I would like the ability to subclass SegmentReader for numerous reasons:

• to capture initialization/close events
• attach custom objects to an instance of a segment reader (caches, statistics, so on and so forth)
• override methods on segment reader as needed

currently this isn't really possible

I propose adding a SegmentReaderFactory that would allow creating custom subclasses of SegmentReader

default implementation would be something like:

public class SegmentReaderFactory {
  public SegmentReader get(boolean readOnly) {
    return readOnly ? new ReadOnlySegmentReader() : new SegmentReader();
  }

  public SegmentReader reopen(SegmentReader reader, boolean readOnly) {
    return newSegmentReader(readOnly);
  }
}

It would then be made possible to pass a SegmentReaderFactory to IndexWriter (for pooled readers) as well as to SegmentReader.get() (DirectoryReader.open, etc)

I could prepare a patch if others think this has merit

Obviously, this API would be "experimental/advanced/will change in future"