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From "Earwin Burrfoot (JIRA)" <>
Subject [jira] Commented: (LUCENE-2355) Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing
Date Tue, 13 Apr 2010 17:37:14 GMT


Earwin Burrfoot commented on LUCENE-2355:

- Norms do both backward and forward sharing of their byte array. Eg, we clone a reader, then
load up norms on the clone, and original sees and uses the same byte array.
This is really complex and likely noone ever needs it. Even if you do hit such a situation,
and norms are loaded twice, first for a clone and then for original reader, it is transient
and norms are really smallish compared to other memory hogs, so we can live with it.
I'm nixing this sharing. Successfully loaded norms are simply inherited from papa-reader.

> Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing
> -------------------------------------------------------------------------
>                 Key: LUCENE-2355
>                 URL:
>             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
> 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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