Too many wait in auth process

[John Stoffel]

>>>>> "ismael" == ismael tanguy at univ-brest fr <ismael.tanguy at univ-brest.fr> writes:


ismael> I'm currently benchmarking new hardware aimed to serve around
ismael> 70k users For now, our IMAP server have 13k users.

This doesn't help us help you.  Is this a new rasperry Pi 4?  Is it a
Dual CPU AMD Rzyzen with 128gb of memory and fast NVMe disks?  What is
your system setup? 

ismael> To run imaptest, I've spwan some bench clients.

Are these tests run from remote hosts?  What kind of network are you
using?  

ismael> Each bench client can run imaptest with 1000 clients.
ismael> More than 1000 clients will load CPU of this bench client

ismael> imaptest command (command are chosen from usage stat on our other IMAP servers):

ismael> imaptest host=xxxxx port=xxx userfile=userfile mbox=/root/dovecot-crlf
ismael>         pass=sxxxx seed=123 clients=1000 select=194 uidfetch=94 noop=70
ismael>         status=82 append=49 fetch=276 list=12 store=19 expunge=22
ismael>         msubs=4 search=4 logout=1 delete=81 no_pipelining

ismael> With one bench client, everything runs smoothly.

ismael> # ps aux | grep dovecot | awk '{print $11,$12,$13,$14,$15,$16,$17,$18}' | sort | uniq -c
ismael>      1 anvil: [221 connections] (anvil)
ismael>    1 auth: [13 wait, 0 passdb, 0 userdb] (auth)
ismael>    1 dovecot/config
ismael>    1 dovecot/imap
ismael>   84 dovecot/imap-login
ismael>    1 dovecot/log
ismael>   20 dovecot/pop3-login
ismael>    1 grep dovecot
ismael>    1 stats: [1307 connections] (stats)

ismael> When a second instance bench instance start imaptest, clients
ismael> of first and second instance begin to stall :

ismael>  1400 stalled for 20 secs in command: 1 LOGIN "fakeuser644 at mailbench...." "password"

So how is your dovecot authentication setup?  Are you using a mysql
backend?  LDAP?  Where is the server you're querying against?  Are you
running mysql on the same server you're running dovecot on?

Are you running multiple dovecot servers with dovecot director in
front of them to help spread the load and to offer resilience if/when
a backend server fails?  

ismael> And :

ismael> # ps aux | grep dovecot | awk '{print $11,$12,$13,$14,$15,$16,$17,$18}' | sort | uniq -c
ismael>    1 anvil: [221 connections] (anvil)
ismael>    1 auth: [1227 wait, 0 passdb, 0 userdb] (auth)
ismael>    1 dovecot/config
ismael>    1 dovecot/imap
ismael>   37 dovecot/imap-login
ismael>    1 dovecot/log
ismael>   20 dovecot/pop3-login
ismael>    1 grep dovecot
ismael>    1 stats: [680 connections] (stats)

ismael> Every auth go in wait, number of connection decreases.

ismael> Using mysql or a password file give same results.

Where is mysql located?  

ismael> I have used different values for service_count with also no success.

Post your configuration details.

ismael> I think my use of imaptest could be false.

It could be.  Are you thinking that 2000 users will all be logging
into the system at the same time?  

ismael> My understanding of service auth is limited for now because
ismael> I'm quite new to Dovecot (I have previously worked with
ismael> Cyrus).

Can't really give you any hints until you tell us more about your
setup.

John