put failed: DB_LOCK_DEADLOCK .....

[ali.pouya@dgi.finances.gouv.fr]

I use an injector with 10 parallel connections to load my directory. I 
often receive this message :

Nov 25 13:37:25 my-server slapd[18333]: => bdb_dn2id_add: put failed: 
DB_LOCK_DEADLOCK: Locker killed to resolve a deadlock -30995

Does somebody know the meaning of the message and what to do to fix it ?
I use openldap 2.3.11.

Thanks
Ali Pouya