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From "Earwin Burrfoot (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2355) Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing
Date Sun, 04 Apr 2010 11:06:27 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2355?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12853244#action_12853244
] 

Earwin Burrfoot commented on LUCENE-2355:
-----------------------------------------

- DR.clone() doesn't do ensureOpen(), you can successfully clone a DR over empty index, or
get weird exception from underlying SR on non-empty index. If you relax synchronized blocks
guarding clone/reopen for readonly readers (which is okay, in theory), it gets even more fun,
as no checks are done when incRefing SR.CoreReaders.

I think I'm going to introduce interface RefCounted, abstract class WhateverRefCounted, which
guards against increment on closed instance and has nice mass-decRef methods in IOUtils.

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