Andrei Dulceanu created OAK-6702:
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Summary: Improve cold standby resiliency to incoherent configs
Key: OAK-6702
URL: https://issues.apache.org/jira/browse/OAK-6702
Project: Jackrabbit Oak
Issue Type: Improvement
Components: segment-tar, tarmk-standby
Affects Versions: 1.7.0
Reporter: Andrei Dulceanu
Assignee: Andrei Dulceanu
In order to correctly configure cold standby there are two OSGi configurations
that need to be provided. Among other settings,
{{org.apache.jackrabbit.oak.segment.SegmentNodeStoreService.config}} needs
{{standby=B"true"}} and
{{org.apache.jackrabbit.oak.segment.standby.store.StandbyStoreService.config}}
needs {{mode="standby"}}. The problem is that sometimes we have
{{mode="standby"}} in {{StandbyStoreService}} and {{standby=B"false"}} in
{{SegmentNodeStoreService}} which leads to starting a problematic standby
instance (with primary behaviour enabled, e.g. indexing, etc.). This problem
stems from the fact that there are two components whose configuration should be
coordinated. Proposals to mitigate this:
# Keep the {{mode="standby"}}, but merge the configuration of
{{StandbyStoreService}} in the one for {{SegmentNodeStoreService}} and
eliminate {{StandbyStoreService}} altogether
# {{StandbyStoreService}} should derive {{mode="standby"}} from
{{"standby=B"true"}} in {{SegmentNodeStoreService}}
# {{SegmentNodeStoreService}} should derive {{"standby=B"true"}} from
{{mode="standby"}} in {{StandbyStoreService}} because that's the way
synchronization happens now: {{StandbyStoreService}} currently waiting for for
a proper initialization of {{SegmentNodeStoreService}}
# Make {{StandbyStoreService}} configuration mandatory, but require a
{{mode="off"}} setting. This way the removal of {{standby=B"true"}} from
{{SegmentNodeStoreService}} would be guaranteed and any synchronization between
the two components would be avoided.
/cc [~frm], [~volteanu], [~mduerig]
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