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https://issues.apache.org/jira/browse/JCR-1213?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12542432
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Ard Schrijvers commented on JCR-1213:
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"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."
I think we have the same end goal: If the index segment instance in which the
parent lookup was found is still valid --> return cached docNumber. This is the
main performance we look for. And I also think we agree on the implementation
regarding the segment instance reference. I only referred to option (1) as the
simple first test for valid cache, and then (2). So, in UUIDDocId, I would
create a weakReference to MultiIndexReader and a seperate one to
CachingIndexReader (a single segment) . If (1) is valid, you are ready,
otherwise check (2). If (1) is equally fast as (2) (performance test) I agree
on removing (1)
I really think we are on the same track, and are talking about the same
mechanism for maintaining the cache. I was referring to a light weight instance
validity test first, and then fall back to the segment instance test. But, as
you indicate, this one might be totally useless in a frequently modifying
workspace.
I'll try to implement some of these options sunday, and try to capture some
performance figures. WDYT?
> 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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