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https://issues.apache.org/jira/browse/JCR-1214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12542065
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Marcel Reutegger commented on JCR-1214:
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For simplicity I would rather use an instance of UUID instead of two longs.
Ard wrote:
> I think we might be able to remove the uuid entirely ...
no, that's not possible. the critical use case is index segment merges.
consider the following index segments:
i1, i2, i3
now let's assume i1 contains a UUIDDocId, which refers to a node in i2. then i2
and i3 are merged and replaced by i4:
i1, i4
on next access to the above mentioned UUIDDocId it will realize that the reader
that was used to get the document number is gone and as a consequence will be
forced to get the document number again and adjust the reader reference to i4.
hope that makes sense... ;)
> DocId.UUIDDocId should not have a string attr uuid, but two long's lsb and
> msb
> -------------------------------------------------------------------------------
>
> Key: JCR-1214
> URL: https://issues.apache.org/jira/browse/JCR-1214
> Project: Jackrabbit
> Issue Type: Improvement
> Components: query
> Affects Versions: 1.3.3
> Reporter: Ard Schrijvers
> Fix For: 1.4
>
>
> After JCR-1213 will be solved, lots of DocId.UUIDDocId can be cached, and not
> being cleaned after every gc(). The number of cached UUIDDocId can grow very
> large, depending on the size of the repository. Therefor, instead of storing
> the private String uuid; we can make it more memory efficient by storing 2
> long's, the lsb and msb of the uuid. Storing 1.000.000 of parent UUIDDocId
> might differ about 100Mb of memory.
> I even did test by removing the entire uuid string, and not use msb or lsb,
> because, when everything works properly (with references to index reader
> segments (See JCR-1213)), the uuid is never needed again: in
> UUIDDocId getDocumentNumber(IndexReader reader) throws IOException {
> we could set uuid = null just before the return. It works perfectly well,
> because when an index reader is recreated, the CachingIndexReader will be
> recreated, hence DocId[] parents will be recreated.
> So, IMO, I think we might be able to remove the uuid entirely when the
> docNumber is found in DocId.UUIDDocId (obviously after JCR-1213)
> WDOT?
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