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https://issues.apache.org/jira/browse/SLING-6070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15565377#comment-15565377
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Stefan Egli commented on SLING-6070:
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bq. Since Oak uses a breadth-first tree traversal when compiling the jcr
events, this fact can be used to detect the earliest possible moment to forward
events, which is as soon as a child traversal has finished. That way, only
parent changes need to be kept, not the entire tree of changes.
Unlike written in the comment, Sling should not make this assumption. So this
statement is actually wrong/useless
> Reduce temporary storage required in JcrResourceListener, call reportChanges
> earlier
> ------------------------------------------------------------------------------------
>
> Key: SLING-6070
> URL: https://issues.apache.org/jira/browse/SLING-6070
> Project: Sling
> Issue Type: Improvement
> Components: JCR
> Affects Versions: JCR Resource 2.8.0
> Reporter: Stefan Egli
> Fix For: JCR Resource 2.8.2
>
>
> As noticed in OAK-4581
> ([here|https://issues.apache.org/jira/browse/OAK-4581?focusedCommentId=15525601&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15525601])
> one advantage of using OakResourceListener over JcrResourceListener (hence
> the term 'optimize for oak' of the config parameter) is that
> OakResourceListener uses a NodeObserver, which calls added/removed/changed
> after each child traversal has finished. This will in turn be used by the
> OakResourceListener to call ObservationReporter.reportChanges. In the
> JcrResourceListener.onEvent case however this is not possible, as the events
> are delivered for each node/property individually, and they first have to be
> 'mapped' to ResourceChanges. This is currently done by keeping maps of
> added/removed/changed ResourceChanges and only after all events (that are
> passed in 1 onEvent) are processed is reportChanges invoked. This has the
> downside of a potentially very large temporary memory usage (these maps can
> get big).
> A suggested improvement is to follow the same pattern as is done in the
> OakResourceListener/NodeObserver pair: to forward the events (by callling
> reportChanges) as early as possible. Since Oak uses a breadth-first tree
> traversal when compiling the jcr events, this fact can be used to detect the
> earliest possible moment to forward events, which is as soon as a child
> traversal has finished. That way, only parent changes need to be kept, not
> the entire tree of changes.
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