negative auth cache?

[Will Yardley]

I am using Dovecot 2.2.13, which doesn't yet seem to have the
$auth_cache_negative parameter. Should the negative cache value honor
$auth_cache_ttl then?

I had a problem where some of our ldap systems were reinitialized. Some
users, presumably those who tried to login while their records were
returning a failure, became unable to login after the records were once
again returning normally.

I currently have:
auth_cache_size = 5 M
auth_cache_ttl = 5 mins
# Not yet implemented
#auth_cache_negative = 2 mins

yet the problem seemed to persist for more than an hour.

Also, how can I flush the cache for a non-default instance's cache using
doveadm -- "doveadm auth cache flush" doesn't seem to have an '-a'
option AFAICT.

# doveadm auth
usage: doveadm [-Dv] [-f <formatter>] auth <command> [<args>]
  cache        flush

w