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 @startuml

title Write or Update flow for Secondary NodeStore
autonumber


participant "NodeStore\nClient" as NS
participant "Document\nNodeStore" as DNS
database "Cache"
database "Secondary Store" as SS
database Mongo

NS -> DNS : Write /a/b@r1

DNS -> Mongo : Write /a/b@r1
DNS -> Cache : Cache /a/b@r1
DNS -> NS    : Commit completed

...
autonumber 1
== Local Change Event==
DNS -> SS    : Content changed event /a/b
SS ->  SS    : Commit changes \n to local store and \n update head revision

...
autonumber 1
== External Change Event==
DNS -> Mongo : Background read for head revision
DNS -> Mongo : Read Journal entry for changes \n done from other cluster nodes
Mongo -> DNS : Changed paths
DNS -> SS    : Content changed event for external changes
SS ->  SS    : Commit changes \n to local store and \n update head revision

...
autonumber 1
== Startup Sync==
DNS -> SS    : Inform observer about current head revision at startup
SS  -> DNS   : Perform diff between local store \n head revision and current head revision
SS ->  SS    : Apply diff \n to local store and \n update head revision

@enduml