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https://issues.apache.org/jira/browse/OAK-4916?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15587657#comment-15587657
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Chetan Mehrotra commented on OAK-4916:
--------------------------------------
[~egli] I would like to review the patch closely but need some more time (2
days?) as wrapping the node bundling feature. Given [~mduerig] implemented most
of these parts it would be helpful if he review this change (and also one in
OAK-4908)
In the meantime it would be useful if we can run the
{{org.apache.jackrabbit.oak.benchmark.ObservationTest}} benchmark that
[~mreutegg] implemented with all these new support. Benchmark would need some
change to ensure that certain commits done are of interest to observer and
certain are just to be filtered out
> Add support for excluding commits to BackgroundObserver
> -------------------------------------------------------
>
> Key: OAK-4916
> URL: https://issues.apache.org/jira/browse/OAK-4916
> Project: Jackrabbit Oak
> Issue Type: Technical task
> Components: core
> Affects Versions: 1.5.11
> Reporter: Stefan Egli
> Assignee: Stefan Egli
> Fix For: 1.6
>
> Attachments: OAK-4916.patch, OAK-4916.v2.patch
>
>
> As part of pre-filtering commits it would be useful to have support in the
> BackgroundObserver (in general) that would allow to exclude certain commits
> from being added to the (BackgroundObserver's) queue, thus keeping the queue
> smaller. The actual filtering is up to subclasses.
> The suggested implementation is as follows:
> * a new method {{isExcluded}} is introduced which represents a subclass hook
> for filtering
> * excluded commits are not added to the queue
> * when multiple commits are excluded subsequently, this is collapsed
> * the first non-excluded commit (ContentChange) added to the queue is marked
> with the last non-excluded root state as the 'previous root'
> * downstream Observers are notified of the exclusion of a commit via a
> special CommitInfo {{NOOP_CHANGE}}: this instructs it to exclude this change
> while at the same time 'fast-forwarding' the root state to the new one.
> ** this extra token is one way of solving the problem that
> {{Observer.contentChanged}} represents a diff between two states but does not
> transport the 'from' state explicitly - that is implicitly taken from the
> previous call to {{contentChanged}}. Thus using such a gap token
> ({{NOOP_CHANGE}}) seems to be the only way to instruct Observers to skip a
> change.
> To repeat: whoever extends BackgroundObserver with filtering must be aware of
> the new {{NOOP_CHANGE}} token. Anyone not doing filtering will not get any
> {{NOOP_CHANGE}} tokens though.
> NOTE: See [comment further
> below|https://issues.apache.org/jira/browse/OAK-4916?focusedCommentId=15572165&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15572165]
> with a new suggested approach, which doesn't use NOOP_CHANGED but introduces
> a new FilteringAwareObserver instead.
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