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https://issues.apache.org/jira/browse/JCR-1213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12543520
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Ard Schrijvers commented on JCR-1213:
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"I think whatever UUIDDocId calculates should be independent of the multi index
reader. That is, it should only hold the document number as retrieved from the
index segment. Then in a second step an offset should be applied"
Yes, this is probably the cleanest way. I now also understand why we had the
discussion about how to solve the issue. You were already thinking about
computing the docNumber in a second step, hence, all that matters is the
segment instance.
So, the latter part, about the segment instance I did build, though we might
discuss wether it is a good way. I added a method to MultiIndexReader
interface,
public boolean hasIndexReaderInstance(IndexReader indexReader);
and in CachingMultiReader and CombinedIndexReader I keep track of subreaders
instances with an IdentityHashMap().
In UUIDDocId I can find the reader instance the doc was found in by changing
SingleTermDocs by having a reference to its segment reader. Obviously, now I
have to cast reader.termDocs(id) to SingleTermDocs which we might not like.
Anyway, I'll try to add the second step offset in calculating the docNumber as
you suggested somewhere this week, and create a patch (might be easier than
talking about a solution).
> 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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