Ashish Chopra created SLING-8854:
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Summary: In-file and In-memory queue-providers for Forward
Distribution report incorrect value for processing "Attempts"
Key: SLING-8854
URL: https://issues.apache.org/jira/browse/SLING-8854
Project: Sling
Issue Type: Bug
Components: Content Distribution
Affects Versions: Content Distribution Core 0.4.0
Reporter: Ashish Chopra
{{ForwardDistributionAgentFactory}} allows specifying "In-Memory" and "In-File"
queue-providers [0]. Both these implementations are provided by
{{SimpleDistributionQueue}} [1].
While responding to a queue-processing request, the head of the queue is
fetched to create a {{DistributionQueueEntry}}, which encapsulates a
{{DistributionQueueItemStatus}}. While retrieving the queue-head-entry, the
number-of-attempts are also incremented by 1, implying _one more_
processing-attempt to have happened on a given queue-item. [2]
The trouble arises from the fact that {{SimpleDistributionQueue#getHead}} ends
up being called from at least three other places:
# Queue status Health Check [3], which is a periodic job
# UI (via {{ExtendedDistributionServiceResourceProvider}}) [4]
# Distribution Queue status MBean [5]
Out of these, #1 is most troublesome - because of its periodic nature, the
number of Attempts for a queue-item that's being processed (or, is blocked)
will keep on increasing without corresponding dequeue-attempts.
Due to #2, everytime the queue status is delivered to the UI, the attempt would
again increase. Similar would be the case of MBean invocations.
This needs to be addressed. Notably, "Sling Jobs" based queue doesn't suffer
from this issue because it relies on retry-counts as maintained by Sling Job
Execution Engine.
[0]
https://github.com/apache/sling-org-apache-sling-distribution-core/blob/deb3d2ae33c4f4678c8503091a9fffdbb141e569/src/main/java/org/apache/sling/distribution/agent/impl/ForwardDistributionAgentFactory.java#L258-L262
[1]
https://github.com/apache/sling-org-apache-sling-distribution-core/blob/deb3d2ae33c4f4678c8503091a9fffdbb141e569/src/main/java/org/apache/sling/distribution/queue/impl/simple/SimpleDistributionQueue.java
[2]
https://github.com/apache/sling-org-apache-sling-distribution-core/blob/deb3d2ae33c4f4678c8503091a9fffdbb141e569/src/main/java/org/apache/sling/distribution/queue/impl/simple/SimpleDistributionQueue.java#L110-L112
[3]
https://github.com/apache/sling-org-apache-sling-distribution-core/blob/deb3d2ae33c4f4678c8503091a9fffdbb141e569/src/main/java/org/apache/sling/distribution/monitor/DistributionQueueHealthCheck.java#L113
[4]
https://github.com/apache/sling-org-apache-sling-distribution-core/blob/deb3d2ae33c4f4678c8503091a9fffdbb141e569/src/main/java/org/apache/sling/distribution/resources/impl/ExtendedDistributionServiceResourceProvider.java#L158
[5]
https://github.com/apache/sling-org-apache-sling-distribution-core/blob/deb3d2ae33c4f4678c8503091a9fffdbb141e569/src/main/java/org/apache/sling/distribution/monitor/impl/DistributionQueueMBeanImpl.java#L62-L91
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