[Dovecot] How to debug slow operation

[zbigniew szalbot]

Hello,

I am no programmer at all. I have dovecot set up on two very similar 
machines. On one of the boxes, the dovecot server has recently been 
showing slower response times. It feels slower. Where it is slower, 
dovecot works as an auth server for postfix. I have replaced exim with 
postfix on that box and I think since then dovecot started to slow down. 
On the other machine the MTA is exim.

I'd like to ask how to go about debugging the problem. Neither machine 
serves many users, the one that is slower has currently only two. It's a 
home setup really.

Here's the output of dovecot -n

# 1.0.5: /usr/local/etc/dovecot.conf
protocols: imap imaps pop3 pop3s
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/local/libexec/dovecot/imap-login
login_executable(imap): /usr/local/libexec/dovecot/imap-login
login_executable(pop3): /usr/local/libexec/dovecot/pop3-login
login_greeting: Server ready.
verbose_proctitle: yes
first_valid_uid: 125
first_valid_gid: 125
mail_extra_groups: mail
mail_location: maildir:/usr/local/virtual/%d/%n
mail_executable(default): /usr/local/libexec/dovecot/imap
mail_executable(imap): /usr/local/libexec/dovecot/imap
mail_executable(pop3): /usr/local/libexec/dovecot/pop3
mail_plugins(default): quota imap_quota
mail_plugins(imap): quota imap_quota
mail_plugins(pop3): quota
mail_plugin_dir(default): /usr/local/lib/dovecot/imap
mail_plugin_dir(imap): /usr/local/lib/dovecot/imap
mail_plugin_dir(pop3): /usr/local/lib/dovecot/pop3
imap_client_workarounds(default): delay-newmail outlook-idle 
netscape-eoh tb-extra-mailbox-sep
imap_client_workarounds(imap): delay-newmail outlook-idle netscape-eoh 
tb-extra-mailbox-sep
imap_client_workarounds(pop3): outlook-idle
pop3_uidl_format(default):
pop3_uidl_format(imap):
pop3_uidl_format(pop3): %08Xu%08Xv
pop3_client_workarounds(default):
pop3_client_workarounds(imap):
pop3_client_workarounds(pop3): outlook-no-nuls oe-ns-eoh
auth default:
  mechanisms: plain login
  passdb:
    driver: sql
    args: /usr/local/etc/dovecot-postfix-sql.conf
  userdb:
    driver: sql
    args: /usr/local/etc/dovecot-postfix-sql.conf
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/auth
      mode: 384
      user: postfix
      group: postfix

Many thanks for your suggestions!

Zbigniew Szalbot