[LUCENE-3631] Remove write access from SegmentReader and possibly move to separate class or IndexWriter/BufferedDeletes/...

• Type: Task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.0-ALPHA
• Component/s: core/index
• Lucene Fields: New
• Assignee: Michael McCandless
• Reporter: Uwe Schindler
• Created: 09/Dec/11 11:53
• Updated: 28/Aug/22 13:03
• Resolved: 20/Dec/11 18:17

Description

After LUCENE-3606 is finished, there are some TODOs:

SegmentReader still contains (package-private) all delete logic including crazy copyOnWrite for validDocs Bits. It would be good, if SegmentReader itsself could be read-only like all other IndexReaders.

There are two possibilities to do this:

1. the simple one: Subclass SegmentReader and make a RWSegmentReader that is only used by IndexWriter/BufferedDeletes/... DirectoryReader will only use the read-only SegmentReader. This would move all TODOs to a separate class. It's reopen/clone method would always create a RO-SegmentReader (for NRT).
2. Remove all write and commit stuff from SegmentReader completely and move it to IndexWriter's readerPool (it must be in readerPool as deletions need a not-changing view on an index snapshot).

Unfortunately the code is so complicated and I have no real experience in those internals of IndexWriter so I did not want to do it with LUCENE-3606, I just separated the code in SegmentReader and marked with TODO. Maybe Mike McCandless can help