Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing
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Key: LUCENE-2355
URL: https://issues.apache.org/jira/browse/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 bound
- 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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