Extremely Slow performance on "All computer page"

Hello All,

We are happy customers of ocsinventory but from sometime we have an issue about performance on the "All comnputer" page, some number of our setup:

Version: 2.1.2 running on centos 6 (recently we upgraded the server from 2.0.x)

"Machines in DB         3844"

We have ocsinventory on a big server 64 GB ram and a lot of cpu :) and load is usually < 0.1

When I click on "show all computers" it takes a couple of minutes, on server I see at the top a mysql process running and on mysql this is the query:

| 16755 | ocs  | localhost | ocsweb | Query   |   31 | Copying to tmp table | select count(*) count_nb_ligne , a.TAG, h.lastdate, h.name, h.ID, h.userid, h.osname, h.memory, h.pr |

Mysql should be tuned.

What can I check/do to improve the speed ?

Or in your experience this behaviour it's "normal" with these numbers ?

Thanks to all