Folder opening / Mailbox problem

[Michael Plate]

Hi,
I'am running a cyrus-imapd 2.1.15 on Gentoo-Linux since 9 month. We use 
lmtp to deliver mail from Postfix. Three weeks ago, we recognized a 
strange problem in accessing folders / mailboxes: it took very long.
I have the usual DB lockers problem in /var/log/messages, but this does 
not seem to be the problem.
Authentification is done by sasl over winbindd and works flawlessly.
When I use cyradm and do lm, it normally takes near to no time to 
display the list (less then 200 users, 3900 Folders).
When having problems it takes 1 minute or longer, and this is 
reproducable. I have increased the file-limit to 16384 (ulimit -n 16384).

The problem occurs weekly or 2 weekly. After the first occurrence it was 
not possible to restart cyrus, because ctl_cyrusdb locked the database 
forever while cleaning (forced it ctl_cyrusdb -r -x).

Machine: 2x Xeon 2.4 GHz / 2048 MB RAM / GDT8524RZ RAID 5 /Intel GigaBit 
Adapter / Gentoo Linux 2.6.8-gentoo-r3 #2 SMP Kernel.

imapd.conf:
-----------
configdirectory:        /var/imap
partition-default:      /var/imap/part
sievedir:               /var/imap/sieve
tls_cert_file:          /etc/cyrusimapd/server.pem
tls_key_file:           /etc/cyrusimapd/server.pem
tls_ca_file:            /etc/cyrusimapd/server.pem
admins:                 xxxxx
hashimapspool:          yes
allowanonymouslogin:    no
allowplaintext:         yes
sasl_pwcheck_method:    saslauthd
autocreatequota: 15000000
altnamespace: yes
sasl_auto_transition: no
tls_cipher_list: TLSv1:SSLv3:SSLv2:!NULL:!EXPORT:!DES:!LOW:@STRENGTH
allowallsubscribe:      no
unixhierarchysep:       yes
lmtp_downcase_rcpt:     yes
cyrusimapd.conf:
----------------
START {
  recover       cmd="ctl_cyrusdb -r"
}
SERVICES {
  imaps         cmd="imapd -s" listen="imaps" prefork=15
  sieve         cmd="timsieved " listen="sieve" prefork=15
  lmtpunix      cmd="lmtpd" listen="/var/imap/socket/lmtp" prefork=15
}
EVENTS {
  checkpoint    cmd="ctl_cyrusdb -c" period=30
  delprune      cmd="ctl_deliver -E 3" period=1440
  tlsprune      cmd="tls_prune" period=1440
  squatter      cmd="squatter -r -s user" period=1440
}
Any ideas, please ?
CU
Michael
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