[Java Broker] Using multiple consumers on a large (e.g. 1million entries+)
queue may become excessively slow
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Key: QPID-3780
URL: https://issues.apache.org/jira/browse/QPID-3780
Project: Qpid
Issue Type: Bug
Components: Java Broker
Affects Versions: 0.14
Reporter: Rob Godfrey
Assignee: Rob Godfrey
Fix For: 0.15
If there are multiple consumers on a queue, a certain percentage of
acknowledgements will not be at the head of the queue because consumers will
not act in lock step. Every time a message not at the head of the queue is
consumed we increment the scavenge count to indicate that we should scan the
queue for deleted entries and remove them. If the queue is very large then
this will take a long time. Clearing down a very large queue with multiple
consumers will thus become very expensive.
We can reduce the cost of scavenging by keeping a record of the high watermark
of deleted entries that weren't at the head of the queue, and only scavenging
the queue to a point beyond the high watermark
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