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From "Earwin Burrfoot (JIRA)" <>
Subject [jira] Created: (LUCENE-2355) Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing
Date Sun, 28 Mar 2010 19:39:27 GMT
Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing

                 Key: LUCENE-2355
             Project: Lucene - Java
          Issue Type: Improvement
            Reporter: Earwin Burrfoot

*Reader lifecycle evolved over time to become some heavily tangled mess. It's hard to understand
what's going on there, it's even harder to add some fields/logic while ensuring that all possible
code paths preserve these fields/interact with the logic properly. While some of said mess
is justified by the task at hand, a big part is just badly done copypaste and can be removed.

I am currently refactoring this and intended to open an issue with a working patch, but the
task winded up somewhat bigger than I expected, so I'm opening it earlier to track stuff encountered/changed/fixed.
The list is by no means exhaustive.
- an iteration to create SRs is copypasted several times, one of them (IW) with wrong iteration
- it is also overly complex and can be folded for create/reopen cases
- readers sent to IndexReaderWarmer are termindexless/docstoreless on some occasions
- it is possible to clone() your way to readwrite NRT reader
- IndexDeletionPolicy is not always preserved through clones/reopens
- cloned readers share CoreReaders and, consequently, updated termsIndex/docStores
- threadlocal versions of fieldsReader/termsVector are bound to SR, not CoreReaders and thus
are recreated on clone/reopen
- double-initialization for some fields (someone got lost and did this to be sure I guess),
stupid assert checks ( qwe = new(); assert qwe != null )
- SR is not always recreated when compound status of underlying segment changes
- deleting already deleted doc marks deletions dirty and rewrites them
- lots of synchronization is done around Reader, while it can be narrowed down to norms/deletions/whatever

I did some structural modifications:
- CompositeReader extracts common code from DirectoryReader and MultiReader (complete)
- ReadonlyDirectoryReader and ReadonlySegmentReader are dead, MutableD/SReaders are introduced
and carry all modification logic/fields (DR complete, SR in progress)
- WriterBackedReader encapsulates NRT reader logic (complete)
- CoreReaders split into CoreReaders, DocStores, TermInfos. All of these are immutable and
SR is cloned when you need to change its mode (in progress)

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