UUIDDocId cache does not work properly because of weakReferences in combination
with new instance for combined indexreader
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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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