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From Apache Wiki <wikidi...@apache.org>
Subject [Jackrabbit Wiki] Update of "Overlay Blob Store" by MattRyan
Date Tue, 25 Jul 2017 22:42:05 GMT
Dear Wiki user,

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The "Overlay Blob Store" page has been changed by MattRyan:
https://wiki.apache.org/jackrabbit/Overlay%20Blob%20Store?action=diff&rev1=2&rev2=3

Comment:
Added curation section and use cases section.

  
  Note that configuring all delegates of an overlay blob store would make the blob store useless
for storing blobs and thus should not be an allowed condition - at least one delegate blob
store must not be a read-only delegate.
  
+ === Curation ===
+ Curation is the process of evaluating the blobs in a blob store to determine if that blob
store is still the correct location for blobs to reside.  In the case of the overlay blob
store, a reason to curate data may be to gradually move data from one level of storage to
a more cost-effective level of storage in a different container or location.
+ 
+ Curation is not in the scope of the overlay blob store; however, it may be prudent to add
common curators to the same package in Oak in future efforts.
+ 
+ == Use Cases ==
+ === Hierarchical Blob Store ===
+ The overlay blob store directly addresses [[JCR Binary Usecase]] UC14 to store data in one
of a number of blob stores based on a hierarchy.
+ 
+ {{drawing:overlay_blob_store_uc14.adraw}}
+ 
+ === Staging Environment ===
+ The overlay blob store can be used to address a production/staging deployment use case,
where one Oak repository is the production repository and another is the staging repository.
 The production repository accesses a single blob store.  The staging repository uses an overlay
blob store to access a staging blob store as well as the production blob store in read-only
mode.  Thus staging can serve blobs out of either blob store but can only modify blobs on
the staging blob store.
+ 
+ {{drawing:overlay_blob_store_uc_stg.adraw}}
+ 
+ === S3DataStore Clustering ===
+ The overlay blob store could be used to address [[JCR Binary Usecase]] UC9, where two Oak
nodes in a cluster may both have a record of a blob in the node store but one node may temporarily
not be able to access the blob in the case of async upload.  This could be addressed by using
an overlay blob store where the first level blob store would be !FileDataStore on an NFS mount
and the second level blob store would be !S3DataStore without a cache.  The overlay blob store
on each node will look for any asset in both the !FileDataStore and the !S3DataStore, thus
avoiding a split-brain scenario.
+ 
+ {{drawing:overlay_blob_store_uc9.adraw}}
+ 

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