dovecot - Sep 2008 - NFS performance and 1.1.3 - what can you (unofficially) get away with?

Hi,

Does anyone have experience with bending the NFS recommendations to get 
better performance?

The question is has anyone, with Maildir and the INDEX= on NFS (i.e. 
dovecot.index and dovecot.index.cache, set mail_nfs_index to no. If so, 
was it better to turn maildir_copy_preserve_filename to on or did it 
help to turn if off. The other question is did you play with turning off 
atime updates or changing the acmin* values?

I know that the recommendation is do not do this. Fortunately Timo's 
screams won't reach my ears for another ten hours. I'm just interested 
if anyone has done this. You are most welcome to reply offline.

I figure that the worst that can happen is that the dovecot.index.cache 
file will become corrupt, and dovecot will then rebuild it. As long as 
this doesn't happen all the time, it should not be a big deal. I'm 
guessing that this is less likely maildir_copy_preserve_filename turned 
on. My old (courier) servers is that I was able to get away with 
disabling atime updates and bumping up acmin* but then there was no 
central index to check.

I admit that this is a nutty way to go since part of the whole point of 
1.1.X is its NFS settings. Yet this is a place with some pretty nutty 
users. (i.e. 2+GB inboxes, 100K messages, one/minute connections, ...)

---Jack

P.S. As a total aside people migrating from 1.0.X to 1.1.3 may wish to 
have to use a different INDEX directory in 1.1.3 than the one you used 
in 1.0.7. Doing this got rid of my index.cache and transaction log error 
messages. This may be why testing isn't showing anything.

P.P.S. I've tried imapproxy for my webmail but it doesn't seem to have 
made much of a difference on the INDEX I/O.

On Wed, 2008-09-10 at 10:58 -0700, Jack Stewart wrote:
> The question is has anyone, with Maildir and the INDEX= on NFS (i.e. 
> dovecot.index and dovecot.index.cache, set mail_nfs_index to no. 
How much worse is the mail_nfs_index=yes? Last I heard it made hardly a
difference.
> If so, 
> was it better to turn maildir_copy_preserve_filename to on or did it 
> help to turn if off.
That shouldn't make a noticeable performance difference. If it's
"yes"
it does one more uidlist lookup, but pretty much always the uidlist is
already in memory in any case so it doesn't matter.
> The other question is did you play with turning off 
> atime updates or changing the acmin* values?
Dovecot doesn't care about atimes, so feel free to disable them.
> I figure that the worst that can happen is that the dovecot.index.cache 
> file will become corrupt, and dovecot will then rebuild it.
It's not the worst that can happen, but index file errors are probably
more likely than other errors..

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Timo Sirainen wrote:
>
>> I figure that the worst that can happen is that the dovecot.index.cache
>> file will become corrupt, and dovecot will then rebuild it.
>>     
>
> It's not the worst that can happen, but index file errors are probably
> more likely than other errors..
>   
I concur!   I currently run one backend NFS server with Dovecot 
installed on it.  In the process of testing adding another dovecot 
front-end server, mounting homedirs via NFS, I managed to delete my 
entire Inbox!    

How?   Dovecot on box1 was using local access, and box2 was using NFS.  
I connected to the same account via both dovecots (imap) at the same 
time.  On box 2 I read my mail and deleted a couple just fine. Then went 
back to box 1, deleted another and the expunge wiped everything out.

Lucky for me I do zfs snapshots nightly and this was right away in the 
morning.

I now have a local NFS mount on box1 to allow for box2 (It's FreeBSD, so 
it still doesn't work right, but at least it errors out 'gracefully'
now).

Rick

The performance hit was bad. When I tried "mail_nfs_index = yes" the 
load went from 0.5 to 120+ (on each of three servers).

My RPM of 1.1.3 includes the Redhat patches from their source RPM for 
1.0.7. I'm checking the patches now and most seem benign but there is 
some mbox locking changes. I'm using maildir so it shouldn't make a 
difference yet I shouldn't need the patches either (using the source RPM 
was a management recommendation).

"mail_nfs_storage" is set to yes. I forgot to put in dovecot -n so it
is
below.

Right now I'm running with local index.cache files for each servers 
(using sticky connections) and that seems to work fine.

---Jack

Timo Sirainen wrote:
> On Wed, 2008-09-10 at 10:58 -0700, Jack Stewart wrote:
>> The question is has anyone, with Maildir and the INDEX= on NFS (i.e. 
>> dovecot.index and dovecot.index.cache, set mail_nfs_index to no. 
> 
> How much worse is the mail_nfs_index=yes? Last I heard it made hardly a
> difference.
> 
>> If so, 
>> was it better to turn maildir_copy_preserve_filename to on or did it 
>> help to turn if off.
> 
> That shouldn't make a noticeable performance difference. If it's
"yes"
> it does one more uidlist lookup, but pretty much always the uidlist is
> already in memory in any case so it doesn't matter.
> 
>> The other question is did you play with turning off 
>> atime updates or changing the acmin* values?
> 
> Dovecot doesn't care about atimes, so feel free to disable them.
> 
>> I figure that the worst that can happen is that the dovecot.index.cache
>> file will become corrupt, and dovecot will then rebuild it.
> 
> It's not the worst that can happen, but index file errors are probably
> more likely than other errors..
> 
/opt/dovecot/sbin/dovecot -n -c /etc/dovecot.conf
# 1.1.3: /etc/dovecot.conf
Warning: fd limit 1024 is lower than what Dovecot can use under full 
load (more than 8192). Either grow the limit or change 
login_max_processes_count and max_mail_processes settings
base_dir: /var/run/dovecot/default/
syslog_facility: local4
listen(default): *:143
listen(imap): *:143
listen(pop3): *:110
ssl_listen(default): *:993
ssl_listen(imap): *:993
ssl_listen(pop3): *:995
ssl_ca_file: /etc/pki/dovecot/certs/caltech-ca.pem
ssl_cert_file: /etc/pki/dovecot/certs/imap.caltech.edu.pem
ssl_key_file: /etc/pki/dovecot/private/imap.caltech.edu.key
login_dir: /var/run/dovecot/default//login
login_executable(default): /opt/dovecot/libexec/dovecot/imap-login
login_executable(imap): /opt/dovecot/libexec/dovecot/imap-login
login_executable(pop3): /opt/dovecot/libexec/dovecot/pop3-login
login_greeting_capability: yes
login_processes_count: 16
login_max_processes_count: 2048
max_mail_processes: 4096
mail_max_userip_connections: 2000
verbose_proctitle: yes
mail_location: 
maildir:/var/spool/maildir/%1Ln/%Ln:INDEX=/var/spool/indexes/%1Ln/%Ln:CONTROL=/var/spool/dovecot/uidl/imap/%1Ln/%Ln
mail_debug: yes
mmap_disable: yes
dotlock_use_excl: no
mail_nfs_storage: yes
mail_executable(default): /opt/dovecot/libexec/dovecot/imap
mail_executable(imap): /opt/dovecot/libexec/dovecot/imap
mail_executable(pop3): /opt/dovecot/libexec/dovecot/pop3
mail_plugins(default): fts fts_squat
mail_plugins(imap): fts fts_squat
mail_plugins(pop3):
mail_plugin_dir(default): /opt/dovecot/lib/dovecot/imap
mail_plugin_dir(imap): /opt/dovecot/lib/dovecot/imap
mail_plugin_dir(pop3): /opt/dovecot/lib/dovecot/pop3
imap_client_workarounds(default): delay-newmail outlook-idle netscape-eoh
imap_client_workarounds(imap): delay-newmail outlook-idle netscape-eoh
imap_client_workarounds(pop3):
pop3_uidl_format(default): %v-%u
pop3_uidl_format(imap): %v-%u
pop3_uidl_format(pop3): %08Xu%08Xv
pop3_client_workarounds(default):
pop3_client_workarounds(imap):
pop3_client_workarounds(pop3): outlook-no-nuls oe-ns-eoh
namespace:
   type: private
   separator: .
   prefix: Mail.
   inbox: yes
   list: yes
   subscriptions: yes
auth default:
   mechanisms: plain login
   passdb:
     driver: ldap
     args: /etc/dovecot.conf-ldap
   userdb:
     driver: static
     args: uid=vmail gid=mail home=/var/spool/maildir/%1Ln/%Ln
   socket:
     type: listen
     master:
       path: /var/run/dovecot/default/auth-master
       mode: 384
       user: vmail
       group: mail
plugin:
   fts: squat
   fts_squat: partial=4 full=8