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https://issues.apache.org/jira/browse/SLING-4751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14567165#comment-14567165
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Stefan Egli commented on SLING-4751:
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With OAK-2829 the goal is to speed up external events a lot thus helping in the
overall goal to avoid hitting the observation queue limit. But that alone still
does not truly scale to infinity: if there are hundreds of servers then
external events become a delicate issue and ideally only very limited number of
external events should have to be processed at all. The problem of having
'mixed' events that occur in case of hitting the limit is - agreed - a nasty
one. But for the rest, maybe it would help to propagate this concept of
'internal vs external' events also to the ResourceListener? Where is this
'internal vs external' event not available other than in case of hitting the
queue limit?
> New Observation Support
> -----------------------
>
> Key: SLING-4751
> URL: https://issues.apache.org/jira/browse/SLING-4751
> Project: Sling
> Issue Type: Improvement
> Components: API, JCR, ResourceResolver
> Reporter: Carsten Ziegeler
> Assignee: Carsten Ziegeler
> Fix For: API 2.10.0, Resource Resolver 1.2.6
>
>
> Mail thread:
> http://mail-archives.apache.org/mod_mbox/sling-dev/201505.mbox/%3C555983F2.20402%40apache.org%3E
> Starting mail
> Right now, resources changes are propagated through event admin - which
> at the time sounded like a good idea. Over time, this has shown to be a
> bottle neck.
> Basically there are at least three problems:
> - the sender of the resource events does not know whether there is a
> receiver, therefore events for each and every change need to be sent
> - event objects are immutable and therefore all relevant data needs to
> be calculated upfront, even if it's not used. For example a resource
> event contains the resource type which needs to be fetched from the
> repository, even if no one is interested in it.
> - receivers of the events can't easily act on behalf of the user who
> initiated the change.
> I created a new listener api at [1] which defines a ResourceListener
> interface and some ways how to specify the events one is interested in.
> The user aware resource listener allows to act on behalf of the user (if
> that information is available).
> On the other side, a new service, the ObservationReporter [2] is
> defined. Resource providers report changes through this interface. The
> payload of such an event is an interface which allows for lazy retrieval
> of the information.
> We can also use this mechanism for compatibility and an implementation
> of the observation reporter might sent all events via the event admin.
> [1]
> https://svn.apache.org/repos/asf/sling/whiteboard/cziegeler/api-v3/src/main/java/org/apache/sling/api/resource/observation/
> [2]
> https://svn.apache.org/repos/asf/sling/whiteboard/cziegeler
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