Uploaded image for project: 'Lucene - Core'
  1. Lucene - Core
  2. LUCENE-2355

Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing


    • Improvement
    • Status: Open
    • Major
    • Resolution: Unresolved
    • None
    • None
    • core/index
    • None
    • New


      *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)


        Issue Links



              Unassigned Unassigned
              earwin Earwin Burrfoot
              0 Vote for this issue
              2 Start watching this issue