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On Tue, 3 Feb 2015, Ron Cleven wrote:
We are gradually rolling out Dovecot (IMAP only, no POP3) to our customer
base. We are replicating between a pair of CentOS 7 boxes. All has been
working wonderfully. However, to be sure our rollout continues to go
smoothly, we put together a simple benchmark client program to fire up X
persistent IMAP connections (using hundreds of mailboxes) that login, list
the folders, select the INBOX, periodically FETCH an email from the INBOX,
and otherwise sit in an IDLE loop. As long as we keep the number of
concurrent IMAP connections under 2k, everything works fine. 2,000 processes
generate a minimal load on the server. However, 2048 is a "hard limit" for
number of IMAP processes on a box the way things are configured right now.
The number (2048) is a bit too magical to be anything but a misconfiguration
of either some kernel limit or a dovecot configuration limit. I have been
unable to figure out where else to look. I have pasted in my dovecot config
below along with the kernel setting for max_user_instances.
Hoping someone can tell me what stupid mistake I have made or what else to
check.
Just an aside, we front-end this with a separate set of proxy servers that
provide an SSL front-end, hence, no SSL in the dovecot config.
/proc/sys/fs/inotify/max_user_instances = 4096
Do you use virtual users? Then this setting is way too low.
There should be entries in kernel log or Dovecot.
- --
Steffen Kaiser
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