userdb prefetch doesn't work with imapc (2.2.18)

[Timo Sirainen]

> On 30 Sep 2015, at 12:19, Nagy, Attila <bra at fsn.hu> wrote:
> 
> Hi,
> 
> I have the following config in dovecot 2.2.18:
> # doveconf -n userdb passdb
> userdb {
>  driver = prefetch
> }
> passdb {
>  args = host=127.0.0.1 port=1430
>  default_fields = userdb_imapc_user=%u userdb_imapc_password=%w
>  driver = imap
> }
> 
> I guess it should cause a single login to the backend IMAP server when issuing a LOGIN to dovecot.
> Yet, dovecot opens two TCP sessions. In the first, it issues a LOGIN and in the second it logs in again (LOGIN) and issues LIST "" "".
> 
> At the end (after LOGIN succeeds to dovecot), only one of the two connections remain open to the backend server.

It's intended to open two TCP sessions. There's no way to fix this without some major changes. Although you could install imapproxy on localhost and have it cache the connection.