Matt Ryan commented on OAK-7083:

I'm going to be moving a conversation from the oak-dev list to the ticket over 
the next few comments.

In doing so, I want to make sure we consider the larger picture.  **It is 
important to remember that right now we are talking about a very specific use 
case of {{CompositeDataStore}}, which is the purpose of this issue:  To support 
the ReadOnly/ReadWrite Delegate scenario.  However, we of course want to avoid 
making design decisions that limit the usability of the {{CompositeDataStore}} 
in the future.  Other uses may not always have exactly one read-only delegate - 
there may be multiple writable delegates, with zero or more read-only 
delegates, in any number of combinations.  I want to avoid designing ourselves 
into a corner where we can't support other use cases easily.


> CompositeDataStore - ReadOnly/ReadWrite Delegate Support
> --------------------------------------------------------
>                 Key: OAK-7083
>                 URL: https://issues.apache.org/jira/browse/OAK-7083
>             Project: Jackrabbit Oak
>          Issue Type: New Feature
>          Components: blob, blob-cloud, blob-cloud-azure, blob-plugins
>            Reporter: Matt Ryan
>            Assignee: Matt Ryan
>            Priority: Major
> Support a specific composite data store use case, which is the following:
> * One instance uses no composite data store, but instead is using a single 
> standard Oak data store (e.g. FileDataStore)
> * Another instance is created by snapshotting the first instance node store, 
> and then uses a composite data store to refer to the first instance's data 
> store read-only, and refers to a second data store as a writable data store
> One way this can be used is in creating a test or staging instance from a 
> production instance.  At creation, the test instance will look like 
> production, but any changes made to the test instance do not affect 
> production.  The test instance can be quickly created from production by 
> cloning only the node store, and not requiring a copy of all the data in the 
> data store.

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