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From Apache Wiki <wikidi...@apache.org>
Subject [Jackrabbit Wiki] Update of "Composite Blob Store Cold Storage Delegates" by MattRyan
Date Tue, 15 Aug 2017 21:44:11 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Jackrabbit Wiki" for change notification.

The "Composite Blob Store Cold Storage Delegates" page has been changed by MattRyan:
https://wiki.apache.org/jackrabbit/Composite%20Blob%20Store%20Cold%20Storage%20Delegates

New page:
= Composite Blob Store Cold Storage Delegates =

NOTE: The current status of this feature is a '''rejected feature''' for Oak 1.8 and a '''possible
future feature''' for later Oak versions.  It would depend on the implementation of some type
of cold storage blob store, which currently does not exist.

== Overview ==
A cold storage delegate is a [[Composite Blob Store]] delegate that stores data in a cold
storage blob store.  This is a blob store that stores data in some form of cold storage, like
AWS Glacier.  The primary feature of cold storage is that read access is not necessarily immediate
and may take some amount of time.  Cold storage services offer copious amounts of storage
for low cost in exchange for very slow access time.  The intended use is long-term archival.

This is a possible future feature that can add value to the composite blob store concept in
the area of auto archival use cases.

== Technical Details ==
=== Impacts on Composite Blob Store ===
The existence of a cold storage delegate may have an impact on the delegate traversal strategy
implementation. For example, an implementation may consider that a cold storage delegate should
always be last resort for read or write requests.  Or an implementation may wish to treat
cold storage delegates as read-only delegates, or take some other approach.

==== Impact on Intelligent Delegate Traversal Strategy ====
If we were to add support for cold storage delegates, it is expected that the following changes
would be added to the Intelligent Delegate Traversal Strategy, which is the default strategy.

===== Delegate Search Order =====
 * Delegates for cold storage reads are always evaluated after every other option is exhausted.
 * Cold-storage delegates are treated as read-only; this strategy would not support writing
to cold storage through the composite blob store.  This may be done via an entirely different
process.

===== Writes =====
Cold-storage delegates are treated as read-only delegates by this traversal strategy.  Writes
must be done via a different custom process.

===== Reads =====
After having tried to read the blob from every other delegate, the algorithm would attempt
to fulfill read request from cold-storage delegates.  Note that since it may take a long time
(e.g. many minutes or hours) to fulfill these requests, a different mechanism for handling
these responses would need to be implemented.

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