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From "Marcel Reutegger (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JCR-1213) UUIDDocId cache does not work properly because of weakReferences in combination with new instance for combined indexreader
Date Wed, 14 Nov 2007 12:04:43 GMT

    [ https://issues.apache.org/jira/browse/JCR-1213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12542427
] 

Marcel Reutegger commented on JCR-1213:
---------------------------------------

> But it is not correct that (1) does not solve anything to the original problem: instead
of the CombinedIndexReader
> which is recreated all the time, I pass in the MultiIndexReader whose instance is kept
as long as no indexes change.

If we can make the MultiIndexReader instance more stable in terms of re-using it as many times
as possible this will of course help us and keep cache entries valid. But since this only
applies to cases where there are no changes to the workspace, it seems to me that this will
not buy use much, except for special occasions where the workspace is not modified for some
time.

> This is at least what I understand from the mechanism, but I am not as familiar as you
are with it ofcourse, so I
> might be off.

your understanding is correct. I guess we just have a differing judgment about when and how
often the cost of building cache entries and maintaining them should be spent.

> UUIDDocId cache does not work properly because of weakReferences in combination with
new instance for combined indexreader 
> ---------------------------------------------------------------------------------------------------------------------------
>
>                 Key: JCR-1213
>                 URL: https://issues.apache.org/jira/browse/JCR-1213
>             Project: Jackrabbit
>          Issue Type: Improvement
>          Components: query
>    Affects Versions: 1.3.3
>            Reporter: Ard Schrijvers
>             Fix For: 1.4
>
>
> Queries that use ChildAxisQuery or DescendantSelfAxisQuery make use of getParent() functions
to know wether the parents are correct and if the result is allowed. The getParent() is called
recursively for every hit, and can become very expensive. Hence, in DocId.UUIDDocId, the parents
are cached. 
> Currently,  docId.UUIDDocId's are cached by having a WeakRefence to the CombinedIndexReader,
but, this CombinedIndexReader is recreated all the time, implying that a gc() is allowed to
remove the 'expensive' cache.
> A much better solution is to not have a weakReference to the CombinedIndexReader, but
to a reference of each indexreader segment. This means, that in getParent(int n) in SearchIndex
the return 
> return id.getDocumentNumber(this) needs to be replaced by return id.getDocumentNumber(subReaders[i]);
and something similar in CachingMultiReader. 
> That is all. Obviously, when a node/property is added/removed/changed, some parts of
the cached DocId.UUIDDocId will be invalid, but mainly small indexes are updated frequently,
which obviously are less expensive to recompute.

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