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https://issues.apache.org/jira/browse/NIFI-2854?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Joseph Witt updated NIFI-2854:
------------------------------
    Description: 
The flowfile, swapfile, provenance, and content repositories play a very 
important roll in NiFi's ability to be safely upgraded and rolled back.  We 
need to have well documented behaviors, designs, and version adherence so that 
users can safely rely on these mechanisms.

Once this is formalized and in place we should update our versioning guidance 
to reflect this as well.

The following would be true from NiFi 1.2.0 onward

* No changes to how the repositories are persisted to disk can be made which 
will break forward/backward compatibility and specifically this means that 
things like the way each is serialized to disk cannot change.
* If changes are made which impact forward or backward compatibility they 
should be reserved for major releases only and should include a utility to help 
users with pre-existing data convert from some older format to the newer 
format.  It may not be feasible to have rollback on major releases.
* The content repository should not be changed within a major release cycle in 
any way that will harm forward or backward compatibility.
* The flow file repository can change in that new fields can be added to 
existing write ahead log record types but no fields can be removed nor can any 
new types be added.  Once a field is considered required it must remain 
required.  Changes may only be made across minor version changes - not 
incremental.
* Swap File storage should follow very similar rules to the flow file 
repository.  Adding a schema to the swap file header may allow some variation 
there but the variation should only be hints to optimize how they're processed 
and not change their behavior otherwise. Changes are only permitted during 
minor version releases.
* Provenance repository changes are only permitted during minor version 
releases.  These changes may include adding or removing fields from existing 
event types.  If a field is considered required it must always be considered 
required.  If a field is removed then it must not be a required field and there 
must be a sensible default an older version could use if that value is not 
found in new data once rolled back.  New event types may be added.  Fields or 
event types not known to older version, if seen after a rollback, will simply 
be ignored.

  was:Currently, if we start up a new version of NiFi and the format of the 
Data Provenance data has changed, we are not able to roll back to a previous 
version of NiFi. If we do, NiFi will fail to read the Provenance Data and not 
start up. We should instead provide the ability to write data to the repository 
in such a way that old versions of the repository will still be able to read 
the data, so that we can roll back


> Enable repositories to support upgrades and rollback in well defined scenarios
> ------------------------------------------------------------------------------
>
>                 Key: NIFI-2854
>                 URL: https://issues.apache.org/jira/browse/NIFI-2854
>             Project: Apache NiFi
>          Issue Type: Improvement
>          Components: Core Framework
>            Reporter: Mark Payne
>            Assignee: Mark Payne
>             Fix For: 1.2.0
>
>
> The flowfile, swapfile, provenance, and content repositories play a very 
> important roll in NiFi's ability to be safely upgraded and rolled back.  We 
> need to have well documented behaviors, designs, and version adherence so 
> that users can safely rely on these mechanisms.
> Once this is formalized and in place we should update our versioning guidance 
> to reflect this as well.
> The following would be true from NiFi 1.2.0 onward
> * No changes to how the repositories are persisted to disk can be made which 
> will break forward/backward compatibility and specifically this means that 
> things like the way each is serialized to disk cannot change.
> * If changes are made which impact forward or backward compatibility they 
> should be reserved for major releases only and should include a utility to 
> help users with pre-existing data convert from some older format to the newer 
> format.  It may not be feasible to have rollback on major releases.
> * The content repository should not be changed within a major release cycle 
> in any way that will harm forward or backward compatibility.
> * The flow file repository can change in that new fields can be added to 
> existing write ahead log record types but no fields can be removed nor can 
> any new types be added.  Once a field is considered required it must remain 
> required.  Changes may only be made across minor version changes - not 
> incremental.
> * Swap File storage should follow very similar rules to the flow file 
> repository.  Adding a schema to the swap file header may allow some variation 
> there but the variation should only be hints to optimize how they're 
> processed and not change their behavior otherwise. Changes are only permitted 
> during minor version releases.
> * Provenance repository changes are only permitted during minor version 
> releases.  These changes may include adding or removing fields from existing 
> event types.  If a field is considered required it must always be considered 
> required.  If a field is removed then it must not be a required field and 
> there must be a sensible default an older version could use if that value is 
> not found in new data once rolled back.  New event types may be added.  
> Fields or event types not known to older version, if seen after a rollback, 
> will simply be ignored.



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