hibernate problems under load

The main issue is:

org.hibernate.AssertionFailure: possible non-threadsafe access to the session,

---------- Forwarded message ----------
From: Okke Harsta <>
Date: Wed, May 11, 2011 at 1:46 AM
Subject: Grouper peformance
To:

Hi Tom,
Just a quick question. We are doing load tests on our infrastructure
and we encounter (0.01 % of the time) an error in Grouper:
Could not execute grouper webservice request: [url:
https://engine:631E9383FD20@grouper.acc.surfconext.nl/grouper-ws/servicesRest/v1_6_000/groups]
[error: ] [http code: 500] [response:
<WsGetMembersResults><resultMetadata><resultCode>PROBLEM_GETTING_MEMBERS</resultCode><resultMessage>There
were 0 successes and 1 failures of getting members for groups.
</resultMessage><success>F</success></resultMetadata><responseMetadata><resultWarnings></resultWarnings><millis>110</millis><serverVersion>1.6.3</serverVersion></responseMetadata><results><WsGetMembersResult><resultMetadata><resultCode>EXCEPTION</resultCode><resultMessage>,
group:
WsGroupLookup[groupName=nl:surfnet:diensten:performance_test_team_493_445,
groupFindResult=SUCCESS], org.hibernate.AssertionFailure: possible
non-threadsafe access to the session,
Problem in HibernateSession: HibernateSession: isNew: true, isReadonly:
true, grouperTransactionType: READONLY_NEW,
Exception in list: (class [Ljava.lang.Object, ByHqlStatic, query:
'select ms, m from MembershipEntry as ms, Member as m where
ms.ownerGroupId = :owner and ms.memberUuid =
:member and ms.memberUuid = m.uuid and ms.enabledDb =
'T'', cacheable: false, cacheRegion:
edu.internet2.middleware.grouper.internal.dao.hib3.Hib3MembershipDAO.FindAllByGroupOwnerAndMemberAndField,
tx type: null, tx type: nullBind var[0]: 'Param (class
java.lang.String):
'owner'->'0ddcb7a7b1db4591b569935b99a6ceed'Bind
var[1]: 'Param (class java.lang.String):
It is only under very heavy load and the root cause appears to be:
http://forum.springsource.org/archive/index.php/t-43437.html
Did you or any of your colleagues ever encountered this?
Thanks,
Okke