Performance problem with V8.1.1

Hello,

We have recently upgraded our DB from 7.1.1 to 8.1.1 and installed OIM 8.1.1.
Every think is fine but we are facing a real performance problem.
The processes are slow to load in jobqueue and simple tasks take minutes to execute.

Example :

It takes 4 minutes between creation of an employee and attribution AD account, and 2 other minutes to add AD group.

The whole process was fast in version 7.1.1

The processes take time to appear in jobqueue .

From time to time, in system journal in  the jobqueue we have  :  Server memory in use: more than 99 percent. DBQueue Processor 10.02.2020 10:58:02 IDM-DB QBM_PWatchDog

and a lot of lines like these ones : 

Resetting DBQueue tasks ADS-K-ADSAccountInADSGroup because processes ADS_ADSAccount_Insert related to objects on these tasks are still running in JobQueue.

DBQueue Processor 10.02.2020 13:40:01 IDM-DB QBM_PSlotResetWhileJobRunning

Resetting DBQueue tasks QER-K-PersonHasQERReuseUS because processes VI_Attestation_Person_new_AttestationCase_for_Certification related to objects on these tasks are still running in JobQueue.
DBQueue Processor 10.02.2020 13:00:15 IDM-DB QBM_PSlotResetWhileJobRunning

i have turned on traceone on the bd, but nothing has changed  : 
DBCC TRACEON (2453,-1)

Thanks for help

BR