hunting the fatty

Christian Kivalo ml+dovecot at
Tue Nov 10 07:50:50 UTC 2015


On 2015-11-10 01:44, mancyborg at wrote:
> Hello dear list,
> I've recently discovered 'doveadm stats' and I'm trying to use
> "doveadm stats dump user" and "doveadm stats dump session"
> to understand the pop/imap users that put more stress on the hard 
> disks.
> My problem is that some users refuse to delete their emails from the 
> server,
> so they keep 20GB of maildir files on the server, the webmail
> (roundcube) takes forever to open the inbox,
> the imap searches takes forever
> and meanwhile all the users wait.
> (already tried roundcube + memcache(d) but didn't help)

What is forever in your context?
I'm using roundcube and a folder with about 78k mails opens in < 1 sec 
unsorted. A folder with about 37k messages from a mailinglist and thread 
sort takes < 3 sec. My roundcube shows 200 messages per page by default.
On a side note, are you using an imap proxy for roundcube? It doesn't 
help you with your dovecot problem but it speeds up roundcube.

To speed up imap searches i can recommend to implement fts-solr with 
dovecot (or maybe fts-elasticsearch, am wanting to try that but solr 
works...). That will speed up your searches after mailboxes are indexed.

> So my problem is not the storage usage itself:
> I don't care if the user gets tons of emails with big attachments;
> my problem is when the user opens / searches an imap folder with more
> than 10K mails
> and iostat util goes 100% for minutes.

Dovecot should be very quick to open even folders with a huge amount of 
files due to its indexes.

I'm unable to reproduce any significant numbers in iostat when accessing 
large mailfolders with roundcube.

Whats your configuration, filesystem, ...

> So I've enabled dovecot's stats and enjoying "doveadm stats top",
> "" and "doveadm stats dump user/session",
> but talking about "doveadm stats dump user" and its output fields:
> user	reset_timestamp	last_update	num_logins	num_cmds	user_cpu	sys_cpu	min_faults	maj_faults	vol_cs	invol_cs	disk_input	disk_output	read_count	read_bytes	write_count	write_bytes	mail_lookup_path	mail_lookup_attr	mail_read_count	mail_read_bytes	mail_cache_hits
> I'm not sure which of those fields can help me
> and I can't find any relevant documentation.
> So here are my questions:
> 1. is there a documentation for those 21 fields and for 'doveadm
> stats' in general ?
> 2. what's the difference between disk_output, read_bytes, read_count
> and mail_read_bytes ?
> 3. which field of those is, in your opinion, more representative for
> expressing the workload that gives me problems ?
> 4. which settings do I need to store 1 week worth of stats ?
> I'm currenty using the 'standard' values:
>   stats_refresh = 30 secs
>   stats_track_cmds = yes
>   stats_memory_limit = 16 M
>   stats_command_min_time = 1 mins
>   stats_domain_min_time = 12 hours
>   stats_ip_min_time = 12 hours
>   stats_session_min_time = 15 mins
>   stats_user_min_time = 1 hours
> Can you please tell me the correct parameters to store 1 week of stats 
> ?

For stats somebody else has to jump in, i have only enabled the plugin 
to see what to get out of it but not made any use of it.

Please share your doveconf -n output

> Thank you,
> Mike


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