[Exim] large retry and wait-remote_smtp files

Hi All,

We are using 3.36 on a large mail server and are trying to reduce some
bottlenecks on our system. I've noticed our retry and wait-remote_smtp files
are quiet large. Both around above the 60mb + mark. Can these be optimized
some other way? Change of lookup type or indexed? We are using mysql lookups
for the user auth if this helps also. Any ways to reduce our bottlenecks
would be great. We are running exim as

/usr/local/exim/bin/exim -bd (for smtp daemon)
and
/usr/local/exim/bin/exim -q5h (for mail queue runner)

as seperate processes, this seems to have sped it up a little, but an strace
on the queue and we see lots of delays, and file locking checks for
/var/spool/mail/db/

-rw-r-----    1 mail     mail     69787648 Dec 12 12:02 retry
-rw-r-----    1 mail     mail            0 Jun  3  2002 retry.lockfile
-rw-r-----    1 mail     mail        12288 Dec 12 12:01
serialize-spam_transport
-rw-r-----    1 mail     mail            0 Dec  3 17:26
serialize-spam_transport.lockfile
-rw-r-----    1 mail     mail     79306752 Dec 12 12:02 wait-remote_smtp
-rw-r-----    1 mail     mail            0 Jun  3  2002
wait-remote_smtp.lockfile
-rw-r-----    1 mail     mail        24576 Dec 12 12:01 wait-spam_transport
-rw-r-----    1 mail     mail            0 Dec  3 17:26
wait-spam_transport.lockfile

Any help would be great, Thanks

Regards,

Paul