[jira] Updated: (JCR-1213) UUIDDocId cache does not work properly because of weakReferences in combination with new instance for combined indexreader

["Ard Schrijvers (JIRA)" <ji...@apache.org>]

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

Ard Schrijvers updated JCR-1213:
--------------------------------

    Attachment: JCR-1213.patch

This is a patch solving the WeakReferences and improving the ChildAxisQuery and DescendantSelfAxisQuery queries speed bu properly caching parent nodex/ hierarchy.

Obviously,  I do not really like the dependency in DocId.UUIDDocId on SingleTermDocs with this patch, and dependency on MultiIndexReader. Perhaps we can change this later. 

For now, perhaps somebody likes to test the patch (specifically on large repositories with ChildAxisQuery  or  DescendantSelfAxisQuery ). Test results for me show an enormous performance gain after the initial queries which are executed with empty caches. 

Hopefully somebody can test it. 

> 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.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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