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From Christian Kohlschütter (JIRA) <j...@apache.org>
Subject [jira] Commented: (LUCENE-2135) IndexReader.close should forcefully evict entries from FieldCache
Date Tue, 08 Dec 2009 20:05:18 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2135?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12787710#action_12787710
] 

Christian Kohlschütter commented on LUCENE-2135:
------------------------------------------------

bq. If I'm reading your patch right, to add something as a user to DirectoryReader+SegmentReader,
I have to extend SegmentReaderIndexCache, IndexCache, then extend SegmentReader and DirectoryReader,
and override all methods in DirectoryReader that create SegmentReader.

No, the functionality you intend to have is just not there at the moment. But it could be
added directly to IndexCache (and thus, to all subclasses of IndexCache automatically).

bq. My aim is to be able to bind stuff to readers without overriding them, delegating, or
touching in any manner except providing certain factories on creation.

We could add getProperty/setProperty methods to IndexCache. You could then bind/get arbitrary
objects as follows:

IndexReader ir = // somehow create your new reader
IndexCache cache = ir.getIndexCache();
Object someObject = cache.getProperty(whatEverKey);
cache.setProperty("org.example.someCoolProperty", anotherObject);

(Personally, I prefer standardized string keys to avoid collisions, just like in the Servlet
API, for example)

Again, this is not yet implemented, but could be done easily, without affecting any existing
IndexReader or the other changes on FieldCache etc.


> IndexReader.close should forcefully evict entries from FieldCache
> -----------------------------------------------------------------
>
>                 Key: LUCENE-2135
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2135
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Index
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 3.1
>
>         Attachments: LUCENE-2135.patch, LUCENE-2135.patch, LUCENE-2135.patch
>
>
> Spinoff of java-user thread "heap memory issues when sorting by a string field".
> We rely on WeakHashMap to hold our FieldCache, keyed by reader.  But this lacks immediacy
on releasing the reference, after a reader is closed.
> WeakHashMap can't free the key until the reader is no longer referenced by the app. And,
apparently, WeakHashMap has a further impl detail that requires invoking one of its methods
for it to notice that a key has just become only weakly reachable.
> To fix this, I think on IR.close we should evict entries from the FieldCache, as long
as the sub-readers are truly closed (refCount dropped to 0).

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