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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2779) Use ConcurrentHashMap in RAMDirectory
Date Fri, 03 Dec 2010 09:23:11 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12966457#action_12966457
] 

Michael McCandless commented on LUCENE-2779:
--------------------------------------------

bq. If the assumption still stands that an IndexInput will not be opened on a "writing" /
unclosed IndexOutput, then RAMFile can also be improved when it comes to concurrency. 

This assumption does still stand, and our unit tests now assert this -- MockDirWrapper throws
an exception if we ever try to open an II when an IO is still open against that file.

That said... we are considering relaxing this, because RT search needs to be able to access
the doc stores with an II even as IO is appending to it.

> Use ConcurrentHashMap in RAMDirectory
> -------------------------------------
>
>                 Key: LUCENE-2779
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2779
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Store
>            Reporter: Shai Erera
>            Assignee: Shai Erera
>            Priority: Minor
>             Fix For: 3.1, 4.0
>
>         Attachments: LUCENE-2779-backwardsfix.patch, LUCENE-2779.patch, LUCENE-2779.patch,
LUCENE-2779.patch, LUCENE-2779.patch, TestCHM.java
>
>
> RAMDirectory synchronizes on its instance in many places to protect access to map of
RAMFiles, in addition to updating the sizeInBytes member. In many places the sync is done
for 'read' purposes, while only in few places we need 'write' access. This looks like a perfect
use case for ConcurrentHashMap
> Also, syncing around sizeInBytes is unnecessary IMO, since it's an AtomicLong ...
> I'll post a patch shortly.

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