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Date: Fri, 3 Dec 2010 04:23:11 -0500 (EST)
From: "Michael McCandless (JIRA)" <jira@apache.org>
To: dev@lucene.apache.org
Subject: [jira] Commented: (LUCENE-2779) Use ConcurrentHashMap in
 RAMDirectory
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    [ 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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