Upgrading from oVirt 4.1.7

hosted-engine VM:

4GB RAM

hosted-engine setup failed, setup log shows this error:

Running upgrade sql script '/usr/share/ovirt-engine/dbscripts/upgrade/04_02_0140_add_max_memory_constraint.sql'...

2017-09-28 16:56:22,951+0100 DEBUG otopi.plugins.ovirt_engine_setup.ovirt_engine.db.schema plugin.execute:926 execute-output: ['/usr/share/ovirt-engine/dbscripts/schema.sh', '-s', 'localhost', '-p', '5432', '-u', 'engine', '-d', 'engine', '-l', '/var/log/ovirt-engine/setup/ovirt-engine-setup-20170928164338-0rkilb.log', '-c', 'apply'] stderr:
psql:/usr/share/ovirt-engine/dbscripts/upgrade/04_02_0140_add_max_memory_constraint.sql:2: ERROR: check constraint "vm_static_max_memory_size_lower_bound" is violated by some row
FATAL: Cannot execute sql command: --file=/usr/share/ovirt-engine/dbscripts/upgrade/04_02_0140_add_max_memory_constraint.sql

2017-09-28 16:56:22,951+0100 ERROR otopi.plugins.ovirt_engine_setup.ovirt_engine.db.schema schema._misc:374 schema.sh: FATAL: Cannot execute sql command: --file=/usr/share/ovirt-engine/dbscripts/upgrade/04_02_0140_add_max_memory_constraint.sql
2017-09-28 16:56:22,952+0100 DEBUG otopi.context context._executeMethod:143 method exception
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/otopi/context.py", line 133, in _executeMethod
method['method']()
File "/usr/share/ovirt-engine/setup/bin/../plugins/ovirt-engine-setup/ovirt-engine/db/schema.py", line 376, in _misc
raise RuntimeError(_('Engine schema refresh failed'))
RuntimeError: Engine schema refresh failed

What's the minimum RAM required now ?

Regards,

Brett