Robbie Gemmell created QPIDJMS-292:
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Summary: consumers may buffer vastly more messages than expected
for their 'prefetch' value
Key: QPIDJMS-292
URL: https://issues.apache.org/jira/browse/QPIDJMS-292
Project: Qpid JMS
Issue Type: Bug
Components: qpid-jms-client
Reporter: Robbie Gemmell
Assignee: Robbie Gemmell
Fix For: 0.23.0
Consumers may buffer vastly more messages than expected for their 'prefetch'
value.
The consumer link credit handling is toggled via the 'prefetch' settings, which
aims to limit the number of messages locally buffered for the consumer,
protecting the consumer and enabling the server to better distribute between
multiple consumers as and when appropriate, particularly ones that arrive later
than others.
The link credit handling however has not been correctly accounting for already
buffered but not yet consumed messages, but rather only the credit itself at
the point of inspection. As a result, if the credit is sufficiently (>=70%)
utilised between processing of messages, more link credit is granted to top up
to the 'prefetch' value, This potentially allows it to buffer more than
<prefetch> messages, and also grant more credit even after it has already done
so. If there is a signficant backlog of messages available and the broker can
feed them to the client quickly enough, and consumption does not similarly keep
up, this can repeat to the extent of buffering as many messages as are
available.
The only obvious workarounds would be reducing the prefetch to 0 or 1.
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