High cpu usage for imapd processes on 2.4.12 (Invoca rpm)

[Guy]

Hi,

I've got an imap server being hammered by a program that is constantly
connecting via IMAP, searching, reading and deleting emails. At a very
rough estimate there'll be 10 to 20 new emails every minute that
arrive, are checked and deleted.

The original machine is running 2.3.16 without replication and the
average load rarely went over 1. On the new server running 2.4.12
(details below) I'm seeing the average load hover around 5 constantly.
The new box is running replication and this appears to be set up
correctly as the logs look pretty clean. top shows CPU percentage for
each imapd process running quite high. The largest mailbox contains
about 3000 emails and is usually at 50 to 60% CPU.

I/O for the machine looks fine, I'm not seeing any iowait or high
usage with iostat. It's using local disks so not something I would
expect to be a problem.

Can anyone suggest where I could start looking to find the cause? Or
point me in the direction of configuration options that are known to
have such an effect after upgrading between the two version?

Thanks
Guy


New server:
name       : Cyrus IMAPD
version    : v2.4.12-Invoca-RPM-2.4.12-2el5_2 63b65d1c 2011-10-04
vendor     : Project Cyrus
support-url: http://www.cyrusimap.org
os         : Linux
os-version : 2.6.18-238.el5
environment: Built w/Cyrus SASL 2.1.22
             Running w/Cyrus SASL 2.1.22
             Built w/OpenSSL 0.9.8e-fips-rhel5 01 Jul 2008
             Running w/OpenSSL 0.9.8e-fips-rhel5 01 Jul 2008
             Built w/zlib 1.2.3
             Running w/zlib 1.2.3
             CMU Sieve 2.4
             TCP Wrappers
             mmap = shared
             lock = fcntl
             nonblock = fcntl
             idle = idled

imapd.conf:
admins: cyradmin cyradmin-repl
configdirectory: /var/lib/imap
delete_mode: immediate
duplicate_db: skiplist
expunge_mode: default
hashimapspool: 1
improved_mboxlist_sort: 1
lmtp_downcase_rcpt: 1
munge8bit: 0
partition-default: /var/spool/imap
ptscache_db: skiplist
sasl_pwcheck_method: saslauthd
sendmail: /usr/sbin/sendmail
sievedir: /var/lib/imap/sieve
statuscache_db: skiplist
sync_authname: cyradmin-repl
server101_sync_host: 10.10.10.10
server201_sync_host: 10.11.10.11
sync_log: 1
sync_log_channels: server101 server201
sync_password: replpass
tls_ca_file: /etc/ssl/certs/domain.com.ca-bundle
tlscache_db: skiplist
tls_cert_file: /etc/ssl/certs/domain.com.crt
tls_key_file: /etc/ssl/certs/domain.com.key
unix_group_enable: 0
normalizeuid: 1


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