auth: Error - Request timed out

[Hajo Locke]

Hello List,

i use dovecot 2.2.22 and have the same problem described here:
https://dovecot.org/pipermail/dovecot/2017-November/110020.html

I can confirm that sometimes there is a problem with connection to 
mysql-db, but sometimes not.
Reasons for failing are still under investigation by my mates.

My current main problem is, that this fail seems to be a one way ticket 
for dovecot. Even if mysql is verifyable working again and waiting for 
connection dovecot stucks furthermore with errors like this:

May 29 07:00:49 hostname dovecot: auth: Error: 
plain(mail at example.com,xxx.xxx.xx.xxx,<HGI4FVFt2Oy80j3P>): Request 999.7 
timed out after 150 secs, state=1

When restarting dovecot all is immediately working again.
Is there a way to tell dovecot to restart auth services or reinitialize 
mysql-connection after these hard fails? I could insert "idle_kill = 1 
mins" into service auth and service auth-worker, but i dont know if this 
would work. Unfortunately i am not able to reproduce this error and 
there are always a couple of days between errors.

Thanks,
Hajo