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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 Tue, 27 Nov 2007 12:30:43 GMT

    [ https://issues.apache.org/jira/browse/JCR-1213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12545805
] 

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

I also expect that the two patches will have similar performance characteristics. In the end
both implement the same idea just slightly different.

In contrast to your patch mine is nearly twice as large and I had to modify many existing
signatures. Instead of IndexReader many methods now deal with concrete extensions of IndexReader.
I'm not sure if this is desirable, but in some occasions it helps to better understand whether
code deals with content just present in one index segment or the overall index.

> When creating a lot of nodes, also remember to "update" a lot of nodes, to create the
'gabs' in the index.

I try to simulate this by running a concurrent thread that modifies content while the test
runs. I plan to run the tests for an hour or two to see what effect it has.

> 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
>
>         Attachments: JCR-1213-mreutegg.patch, JCR-1213.patch
>
>
> 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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