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https://issues.apache.org/jira/browse/IMAP-371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13637842#comment-13637842
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Andrzej Rusin commented on IMAP-371:
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Hi Eric,
I investigated it more. Looks like this approach probably won't be enough,
because the clients seem to periodically call SELECT on all known folders to
check for messages/changes. And when there is many clients, they still would
load the Mailbox huge amount of times, and get some of its metadata too.
I have another idea of a more heavy-handed approach, which I will discuss in
separate issue.
> MailboxManager::getMailbox called very often
> --------------------------------------------
>
> Key: IMAP-371
> URL: https://issues.apache.org/jira/browse/IMAP-371
> Project: James Imap
> Issue Type: Improvement
> Components: Processor
> Affects Versions: 0.3
> Reporter: Andrzej Rusin
> Assignee: Eric Charles
>
> MailboxManager::getMailbox(MailboxPath mailboxPath, MailboxSession session)
> is getting called extremely often.
> On my custom RDBMS-based Mailstore implementation it is the biggest hot spot.
> I had to resort to caching the return value of it on Memcache, but even after
> that it uses up around 15% of spent CPU time. It is far too much in my
> opinion. (before I started caching it, fully indexed RDBMS getting of the
> mailbox was taking more than 50% of the global RDBMS load).
> My suspect is the method AbstractMailboxProcessor::addFlagsResponses(final
> ImapSession session, final SelectedMailbox selected, final
> ImapProcessor.Responder responder, boolean useUid).
> It gets the mailbox from MessageManager each time, even if it may be not
> needed.
> This method is called in many CommandProcessors during the
> unsolicitedResponses phase.
> After I am able to really profile and confirm that it's the core of problem,
> I will provide a patch.
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