Hi,

I introduced the passive queues in SLING-4629 and I am trying to recall the 
exact context __.  
An active queue is a queue for which a processor was defined and a passive 
queue is one for which no processor was defined. 

If I recall correctly the first usecase was to implement a multi-datacenter 
sync. In a datacenter there was an author instance that coordinated the sync 
between publish instances in that datacenter using active queues but also saved 
the packages in a passive queue for other datacenters to pull the updates.

The second usecase was to pause delivery of some queues. Assume that one 
endpoint is down for a long time and you want to pause delivery to it, but 
still build the queue, then you make the queue for that endpoint passive.

Marius


https://github.com/apache/sling-org-apache-sling-distribution-core/commit/0a6508e42034721a97eb2f86f9ede591f09db7fe
 



On 18/11/2019, 12:23, "Ashish Chopra" <[email protected]> wrote:

    Hi,
    
    I'm trying to better understand agent instances created via 
QueueDistributionAgentFactory [0], and the Resource-backed queues they leverage 
[1].
    The Sling issue through which this implementation was added makes a mention 
of Active and Passive queues (as defined as [2]), with [1] being a Passive 
queue primarily useful for Reverse Distribution.
    
    I hope to be able to leverage Resource-backed queues for 
forward-distribution scenarios, but currently it is not possible (given [1] and 
[2]). I'm working to understand existing "active" queue impls in 
sling-dist-core bundle [3] to have a better sense of what would it take to 
develop an "active" variant of ResourceQueue impl.
    
    I have a few queries on the topic above:
    * is there any documentation (beyond [2], that is) which explains the 
concept of Passive and Active queues (in context of SCD) in more detail?
    * is there any background information on why ResourceQueue impl [1] is 
currently Passive? i.e., was it due to any known limitations, or a case of 
YAGNI?
    
    I read through SLING-7754 and searched the archives, but couldn't get any 
pointers. Would be great if the community can help me discover more information 
on this topic.
    
    Thanks
    Ashish
    
    [0] 
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