Failed to get quota resource STORAGE/MESSAGE

[Thomas Barth]

Hello,
I would like to activate quota, but I get the following error. Any idea 
why it can't be found and why the mapped dbfields "bytes" and "messages" 
remain empty (0)?

doveadm quota get -u user at domain.de

doveadm(user at domain.de): Error: Failed to get quota resource STORAGE: 
quota-dict: dict_lookup(priv/quota/storage) failed: Connection closed 
(reply took 0.000 secs (0.001 in dict wait, 0.000 in other ioloops, 
0.000 in locks))
doveadm(user at domain.de): Error: Failed to get quota resource MESSAGE: 
quota-dict: dict_lookup(priv/quota/messages) failed: Connection closed 
(reply took 0.000 secs (0.001 in dict wait, 0.000 in other ioloops, 
0.000 in locks))
Quota name Type    Value Limit                                           
                                                  %
User quota STORAGE error error                                           
                                              error
User quota MESSAGE error error

##############

priv/quota/storage is defined in the file: 
/etc/dovecot/dovecot-sql.conf.ext

map {
   pattern = priv/quota/storage
   table = mailusers
   username_field = account
   value_field = bytes
}
map {
   pattern = priv/quota/messages
   table = mailusers
   username_field = account
   value_field = messages
}

##############

Now with Debug-Parameter

doveadm -D quota get -u user at domain.de 2>&1 | awk -FDebug: '{print $2}'

A few skipping messages skipped

  Skipping module ..., because dlopen() failed: ... (this is usually 
intentional, so just ignore this message)
  [...]
  auth-master: userdb lookup(users at domain.de): Started userdb lookup
  auth-master: conn unix:/run/dovecot/auth-userdb: Connecting
  auth-master: conn unix:/run/dovecot/auth-userdb (pid=33004,uid=0): 
Client connected (fd=9)
  auth-master: userdb lookup(users at domain.de): auth USER input: 
users at domain.de home=/data/vmail/user_conf/domain.de/user uid=5001 
gid=5001 mail=maildir:/data/vmail/domain.de/users/ 
quota_rule=*:bytes=10737418240
  auth-master: userdb lookup(users at domain.de): Finished userdb lookup 
(username=users at domain.de home=/data/vmail/user_conf/domain.de/user 
uid=5001 gid=5001 mail=maildir:/data/vmail/domain.de/users/ 
quota_rule=*:bytes=10737418240)
  Added userdb setting: mail=maildir:/data/vmail/domain.de/user/
  Added userdb setting: plugin/quota_rule=*:bytes=10737418240
  Effective uid=5001, gid=5001, home=/data/vmail/user_conf/domain.de/user
  Quota root: name=User quota backend=dict args=:proxy::quota
  Quota rule: root=User quota mailbox=* bytes=10737418240 messages=0
  Quota rule: root=User quota mailbox=Trash bytes=+104857600 messages=0
  Quota warning: bytes=10200547328 (95%) messages=0 reverse=no 
command=quota-warning 95 user at domain.de
  Quota warning: bytes=8589934592 (80%) messages=0 reverse=no 
command=quota-warning 80 user at domain.de
  Quota grace: root=User quota bytes=1073741824 (10%)
  quota-dict: user=user at domain.de, uri=proxy::quota, noenforcing=0
  dict(proxy): dict created (uri=proxy::quota, base_dir=/run/dovecot)
  open(/proc/self/io) failed: Permission denied
  Namespace inbox: type=private, prefix=, sep=., inbox=yes, hidden=no, 
list=yes, subscriptions=yes location=maildir:/data/vmail/domain.de/user/
  maildir++: root=/data/vmail/domain.de/user, index=, indexpvt=, 
control=, inbox=/data/vmail/domain.de/user, alt=
  quota: quota_over_flag check: quota_over_script unset - skipping
  dict(proxy): Looking up 'priv/quota/storage'
  dict(proxy): Looking up (async) 'priv/quota/storage'
  dict(proxy): conn unix:/run/dovecot/dict: Connecting
  dict(proxy): conn unix:/run/dovecot/dict (pid=33004,uid=0): Client 
connected (fd=10)
  dict(proxy): Lookup finished for 'priv/quota/storage': not found
  dict(proxy): conn unix:/run/dovecot/dict (pid=33004,uid=0): 
Disconnected: Connection closed (fd=10)
  dict(proxy): Lookup finished for 'priv/quota/storage': not found

  dict(proxy): Looking up 'priv/quota/messages'
  dict(proxy): Looking up (async) 'priv/quota/messages'
  dict(proxy): conn unix:/run/dovecot/dict (pid=33004,uid=0): Connecting
  dict(proxy): conn unix:/run/dovecot/dict (pid=33004,uid=0): Client 
connected (fd=10)
  dict(proxy): Lookup finished for 'priv/quota/messages': not found
  dict(proxy): conn unix:/run/dovecot/dict (pid=33004,uid=0): 
Disconnected: Connection closed (fd=10)
  dict(proxy): Lookup finished for 'priv/quota/messages': not found

  User session is finished
  dict(proxy): Waiting for dict to finish pending operations
  dict(proxy): dict destroyed
  auth-master: conn unix:/run/dovecot/auth-userdb (pid=33004,uid=0): 
Disconnected: Connection closed (fd=9)

##############

recalc is setting 'priv/quota/storage' and 'priv/quota/messages', but 
where? The mapped dbfields "bytes" and "messages" remain empty (0)!

doveadm -D quota recalc -u user at domain 2>&1 | awk -FDebug: '{print $2}'

last lines of output

  dict(proxy): Waiting for dict to finish pending operations
  dict(proxy): Starting transaction
  dict(proxy): Unsetting 'priv/quota/storage'
  dict(proxy): conn unix:/run/dovecot/dict: Connecting
  dict(proxy): conn unix:/run/dovecot/dict (pid=34968,uid=0): Client 
connected (fd=20)
  dict(proxy): Unsetting 'priv/quota/messages'
  dict(proxy): Setting 'priv/quota/storage' to '608708975'
  dict(proxy): Setting 'priv/quota/messages' to '30657'
  quota-dict: Quota recalculated: count=30657 bytes=608708975
  dict(proxy): Waiting for dict to finish pending operations
  dict(proxy): Dict transaction finished
  dict(proxy): conn unix:/run/dovecot/dict (pid=34968,uid=0): 
Disconnected: Connection closed (fd=20)
  User session is finished
  dict(proxy): Waiting for dict to finish pending operations
  dict(proxy): dict destroyed
  auth-master: conn unix:/run/dovecot/auth-userdb (pid=34968,uid=0): 
Disconnected: Connection closed (fd=9)

###############

I used the following nice documentation as a guide: 
https://www.linuxbabe.com/mail-server/user-quota-postfixadmin-dovecot, 
but it gives no further infomations to this error.