Stefan Egli created OAK-4916:
--------------------------------
Summary: 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
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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
