[jira] [Commented] (OAK-4180) Use Segment NodeStore as a local cache for a remote Document store

["Chetan Mehrotra (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-4180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15286104#comment-15286104 ] 

Chetan Mehrotra commented on OAK-4180:
--------------------------------------

Current work in progress is at https://github.com/chetanmeh/jackrabbit-oak/tree/OAK-4180

> Use Segment NodeStore as a local cache for a remote Document store
> ------------------------------------------------------------------
>
>                 Key: OAK-4180
>                 URL: https://issues.apache.org/jira/browse/OAK-4180
>             Project: Jackrabbit Oak
>          Issue Type: New Feature
>          Components: documentmk
>            Reporter: Chetan Mehrotra
>            Assignee: Chetan Mehrotra
>             Fix For: 1.6
>
>         Attachments: OAK-4180-v1.patch
>
>
> DocumentNodeStore makes use of persistent cache to speed up its processing and save on making remote calls for data already present in cache
> In addition to that we can look into make use of Segment NodeStore as kind of "local copy" for certain paths in repository and route calls to it if possible. As part of this task I would like to prototype such an approach. At high level it would work as below
> # At start bootstrap the setup and shutdown it down
> # Use a modified "sidegrade" and copy over the NodeStats from Document store to Segment store. In such a copy we also store some Document specific properties like {{readRevision}} and {{lastRevision}} as hidden property in Segment NodeStates
> # In DocumentNodeStore we refactor the current code to extract a 
> ## {{AbstractDocumentNodeState}} - Abase class which has some logic move out from {{DocumentNodeState}}
> ## {{SegmentDocumentNodeState}} extends above and delegate calls to a wrapped {{SegmentNodeState}}
> ## {{DocumentNodeState}} would also extend {{AbstractDocumentNodeState}} and hence delegate to some calls to parent. In this when a call comes for {{getChildNode}} it can check if that can be served by a local copy of {{SegmentNodeStore}} for given {{rootRevision}} then it delegates to that
> # For update plan is to make use of {{Observer}} which listens to changes and updates the local copy for certain configured paths. 
> ## Key aspect to address here is handle the restart case where in a cluster a specific node restarts after some time then how it refreshes itself there
> *Currently its in a prototype phase*



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