[jira] Commented: (LUCENE-2355) Refactor Directory/Multi/SegmentReader creation/reopening/cloning/closing

["Earwin Burrfoot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-2355?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12852417#action_12852417 ] 

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

Some more stuff I forgot:

- No need to keep around origInstance in CoreReaders. It is used to purge FieldCache, but the cache is purged based on getFieldCacheKey, which is common across all clones/reopens
- MultiReader-level norms cache is not needed with per-segment searching and is removed. The method that extracts norms into a user-passed array still has the same performance even without the cache.

> 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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