Gary Tully created AMQ-5920:
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Summary: Improve performance of virtual topic fanout
Key: AMQ-5920
URL: https://issues.apache.org/jira/browse/AMQ-5920
Project: ActiveMQ
Issue Type: Improvement
Components: Broker
Affects Versions: 5.11.0
Reporter: Gary Tully
Assignee: Gary Tully
Fix For: 5.12.0
Virtual topics provide a nice alternative to durable subs. Each durable sub is
modeled as a separate queue.
There are performance implications however, because a message has to be sent to
each of the (fanout) queues. For a durable subs, there is a single message in
the journal and just index updates for each sub.
To improve performance there are three ways to improve the comparison between
virtual topics and durable subs.
# avoid the disk sync associated with enqueue
# do parallel enqueues to get the store batching writes
# introduce message references in the journal to reduce the disk io
For 1, introducing a transaction (either client side or automatically, broker
side) ensures there is a single disk sync on commit.
For 2, using an executor to do sends in parallel allows the journal to batch as
seen in AMQ-5077
For 3, the implementation is a lot more involved; for recovery there needs to
be a journal write per destination and reading the journal will require two
reads because of the indirection. Tracking gc needs to be handled to ensure the
referenced entry is maintained. In short this is a lot of work and will only be
visible for large (> 8k) messages where the cost of a large v small journal
write is noticeable. The messageId dataLocator provides an entry point for this
work but considering that 1 & 2 combined can give a 3x improvement I don't
think it is worth the effort (and added complexity) at the moment.
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