Excessive NIO write buffering leads to mailboxd service outage
AFFECTED ZCS VERSIONS
7.x, 8.0.0, 8.0.1, 8.0.2, 8.0.3, 8.0.4
Excessive write buffering in NIO caused by slow clients can lead to mailboxd memory over-utilization which can result in a service outage. The write buffer fills the available heap allocated to mailboxd which can result in an endless loop of major garbage collection.
The issue occurs when NIO for IMAP is enabled on the mailbox server. In 7.x, NIO is disabled by default. In Zimbra 8, NIO is enabled by default. Client symptoms include sluggishness or lack of response (hangs) while communicating with an affected ZCS mailbox server. ZCS server to server traffic can also be affected.
NIO imap, NIOSocketSession leaking - Fix targeted for the 8.0.5 release.
Disable IMAP NIO and restart mailboxd.
zmlocalconfig -e nio_imap_enabled=false