dovecot - Aug 2022 - dovecot/config processes open, and consuming all memory

From: Aki Tuomi <aki.tuomi at open-xchange.com>
> The *default* configuration for service config is usually just fine.
> Is there some reason you decided to modify it in first place?

Are you asking me, or the OP?


I guess the blunt answer is ignorance on my part.  However, I pointed

out that the docs about this setting is somewhat misleading -- it's used

to limit any potential memory leaks for long-lived processes by ensuring

it terminates periodically.


I read this and thought to myself "this is a good thing to do",
without

realizing that it would have the opposite effect as lingering clients

could delay service termination indefinitely.  The side effect is many

new processes are spawned to handle new clients, and eventually

the maximum process limit is reached, and chaos ensues.


So for services like imap-login and others that can have lingering

clients, the only sensible values for service_limit is {0,1}.  If you

set service_limit>1, the asymptotic behaviour is like service_limit=1,

and process_limit would have to be adjusted accordingly.


The docs can explain this rather wordy and subtle explanation of

service_limit, or service_limit can be constrained to values {0,1} so that

others don't blunder along the same path I did.


Joseph Tam <jtam.home at gmail.com>

> On 17/08/2022 00:57 EEST Joseph Tam <jtam.home at gmail.com> wrote:
> 
>  
> From: Aki Tuomi <aki.tuomi at open-xchange.com>
> 
> > The *default* configuration for service config is usually just fine.
> 
> > Is there some reason you decided to modify it in first place?
> 
> 
> Are you asking me, or the OP?
> 
> 
> I guess the blunt answer is ignorance on my part.  However, I pointed
> 
> out that the docs about this setting is somewhat misleading -- it's
used
> 
> to limit any potential memory leaks for long-lived processes by ensuring
> 
> it terminates periodically.
> 
> 
> I read this and thought to myself "this is a good thing to do",
without
> 
> realizing that it would have the opposite effect as lingering clients
> 
> could delay service termination indefinitely.  The side effect is many
> 
> new processes are spawned to handle new clients, and eventually
> 
> the maximum process limit is reached, and chaos ensues.
> 
> 
> So for services like imap-login and others that can have lingering
> 
> clients, the only sensible values for service_limit is {0,1}.  If you
> 
> set service_limit>1, the asymptotic behaviour is like service_limit=1,
> 
> and process_limit would have to be adjusted accordingly.
> 
> 
> The docs can explain this rather wordy and subtle explanation of
> 
> service_limit, or service_limit can be constrained to values {0,1} so that
> 
> others don't blunder along the same path I did.
> 
> 
> Joseph Tam <jtam.home at gmail.com>
Thanks for the feedback, and sharing this. 

Aki