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https://issues.apache.org/jira/browse/JAMES-3191?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17115825#comment-17115825
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Benoit Tellier commented on JAMES-3191:
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> Did you run a profiler or use glowroot APM to have some insights on where the
> time is spent exactly ?
Well, I used the glowroot APM but observation in rabbitMQ admin api shows
messages are not consumed fast enough and queues are growing, and Grafana
boards also support this analysis.
I posted all relevant details in a (private) Linagora operational ticket.
> I have serious doubt that raising channel number from 3 to 10 will change
> latency from several minutes to some milliseconds
> 1. How did you discovered it was related to the channel number?
That's a blind proposition that of course need to be fact checked.
(I have no real better idea to be honnest)
> Why do we need RabbitMQ for a SELECT?
Easy. Because:
- 1. You need propagating IMAP unsolicitated notifications, that happens upon
changes triggered by another protocol session
- 2. Maintain the IMAP MSN <-> UID mapping
So SelectedMailboxImpl is a mailbox that can be registered to get updates for
that given mailbox.
> Maybe it is not the channel problem, but the lock time, in this case, we
> might do more than just sending a message over RabbitMQ, and we should
> prepare the message, then request the channel.
That could be related to the change removing the ".block() call" in
ReactorRabbitMQChannelPool::borrow().
4d0da67 `JAMES-2774 Avoid nested block in ReactorRabbitMQChannelPool` is IMO a
suspect...
> Key registration is slow
> ------------------------
>
> Key: JAMES-3191
> URL: https://issues.apache.org/jira/browse/JAMES-3191
> Project: James Server
> Issue Type: Improvement
> Components: eventbus, IMAPServer
> Affects Versions: master
> Reporter: Benoit Tellier
> Priority: Major
> Labels: perf
>
> We noticed that on *master* SELECT IMAP command is significatively slow
> (several minutes) on top of the distributed profile. (See attached
> instrumentation average time and percentiles)
> A quick performance review links this to listener registration (by key).
> A code review leads to:
> - The low channel number (3) maybe this count can be safely raised to a
> higher number? Like 10? Maybe even configurable?
> - EventBus::Register operation is handling IO but is synchronous. The
> reactor scheduler backing it up is unspecifed (thus is likely the parrallel
> one). We should let the caller specify the scheduler he whishes to run.
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