AEM / CQ 6.0 - JCR block Repository Writes unsupported (necessary for hot backups)

[miqk]

Hi,

When attempting a "blockRepositoryWrites" via /system/console/jmx, I am getting a "javax.jcr.UnsupportedRepositoryOperationException".  When will this functionality be supported, as it is needed for performing online backups?  See screenshot for java error/stacktrace.

Thanks.

Michael C.

[justin_at_adobe · Accepted solution]

Hi,

That call is not necessary for a hot backup if you are using Oak.

Regards,

Justin

[miqk]

Thanks Justin.  How is blocking repository writes, or its equivalent done in Oak then?  

[justin_at_adobe]

Like I said, this isn't necessary. As such, there's no way to do it.

[miqk]

Why is blocking writes not necessary?  What practical way is there then to have a clean backup of Oak & TarMK without shutting down the CQ application? With CQ 5.5/5.6 the blockRepositoryWrites command conveniently allowed for a system adminstrator to do a point-in-time volume snapshot, capturing the repository state for that point in time.  What similar method in CQ6 is there for this?  And I am not referring to the old way of doing online CQ backups which basically copies the entire repository to another folder - this was CPU as well as disk intensive, and was not practically for large (>100GB) repositories.

[justin_at_adobe]

Due to the way that MVCC is used in Oak, if you want to create a filesystem snapshot, you do not need to block repository writes.

[miqk]

What is the way then to create online backups in CQ without shutting down the application?

[miqk]

Justin, can you provide the documentation that describes this?  I just want to make sure that this is a supported backup method.

[justin_at_adobe]

I'm not aware of public documentation for this. I've created an internal documentation request. Feel free to file a DayCare issue indicating that this is a priority for you and reference DOC-4746.

[Mschilli]

Sorry if I'm being thick here..

Are you saying that OAK can handle an Linux LVM SNAPSHOT  without shutting down the instance, or blocking writes?

And, IF this is the case, why 7 months later has that documentation not made it to the official documentation?

Thanks!
Matt

[AllDayDev]

I think your questions/interest on this is a very good thing.

I have seen some documentation on this change - some for Oak and some for AEM.

For example:

 https://docs.adobe.com/docs/en/aem/6-0/deploy/upgrade/introduction-to-oak.html#What is different from Jackrabbit 2?

http://jackrabbit.apache.org/oak/docs/differences.html

http://jackrabbit.apache.org/oak/docs/dos_and_donts.html

https://cqdump.wordpress.com/2014/06/24/aem-6-0-and-apache-oak-what-has-changed/

I definitely encourage you to follow up via DayCare (referencing the issue Justin mentioned) to request further documentation, because we could do a better job in clearly stating the real-world implications on this change (e.g. no longer needing to block repo writes when taking a volume snapshot).

HTH!

- Carey