DLR problem & SMS submit speed

Dear All,
We have a kannel instance, without MYSQL DLR DB.
When we are making an SMS broadcast (around 500K SMS at once) without
delivery reports request, we get a speed of 40 SMS per second, as allowed
by our SMSc.

If we make broadcast with DLR mask = 31, after on server are kept in
internal storage more than 100K DLR reports, the submit SMS starting to
work very slow, it comes to something like this:

Kannel bearerbox version `1.4.3'. Build `Feb 8 2013 05:24:31', compiler
`4.6.3'. System Linux, release 3.2.0-36-virtual, version #57-Ubuntu SMP Tue
Jan 8 22:04:49 UTC 2013, machine x86_64. Hostname
ip-10-32-40-5.eu-west-1.compute.internal, IP 10.32.40.5. Libxml version
2.7.8. Compiled with MySQL 5.5.29, using MySQL 5.5.29. Using native malloc.
DLR: 128998 queued, using internal storage
(online 132773s, rcvd 915, dlr 1029929, sent 922199, failed 0, queued
508667 msgs)

Did somebody faced this kind of issues? any advice?

-- 
Best regards,
George Karagheaur
Mob: +79165482960
Skype: george.karagheaur
Email/MSN: [email protected]