Michal Zerola created QPID-4779:
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Summary: Implementation of policies for queues in Java Qpid Broker
Key: QPID-4779
URL: https://issues.apache.org/jira/browse/QPID-4779
Project: Qpid
Issue Type: Improvement
Components: Java Broker
Affects Versions: Future
Reporter: Michal Zerola
Priority: Minor
Fix For: Future
Hi,
currently the Java Broker doesn't provide the same policies for queues like C++
Broker does. In particular, there is no option to hard limit the maximum number
of messages for queue and instruct the broker to act according to some policy
if there is an attempt to exceed this limit.
I think it would be nice to have possibility to set queue to REJECT or
RING-TYPE policy like in C++ version.
In the attachment is a dirty-prototype using which I am trying to outline the
main idea of possible implementation. Please, consider it is as an illustration
of the principle, there is definitely more (technical) work needed (including
tests).
Some explanation along the way:
REJECT policy:
The idea should be quite straight-forward. If the new message is supposed to be
enqueued on some queue which current depth is already at the limit, the message
should be rejected.
RING policy:
Each queue should be able to delete the least important message and create the
free slot for new incoming message if the limit is met. The definition of least
important differs among the queue types. For standard queue, it should be the
oldest message, which can be easily found at the head of the queue. For
priority queues (inspired by C++ implementation) it should be the oldest
message with the lowest priority. For sorted queues I leave this up to
discussion. Personally, I would assume that oldest message is the least
important.
NONE policy:
Current situation, the queue grows until JVM memory limits allow it.
As you can see from the patch, I have added the decision what to do with the
message into the postCommit() method of PostEnqueueAction. According to the
policy type, the new message is either rejected (AMQException thrown) or
enqueued. In the case of RING policy, the least important message is deleted.
I have added the method deleteLowestPriorityEntry() into the AMQQueue. The
implementation in SimpleAMQQueue illustrates the idea - try to acquire and
delete the least priority entry. To find the lowest priority entry from the
entry list I have added the new iterator into the QueueEntryList interface.
Each implementation can have different way how to find such an entry.
SimpleAMQQueueEntryList just takes the first (oldest one). PriorityQueueList
starts with the oldest with the lowest priority entry. I have not implemented
yet the version for Sorted queues.
Please try to look into the patch and let me know if the implementation based
on this idea would be reasonable. I will provide the enhanced version of the
patch then.
Thank you.
Michal
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