[PATCH] Enable Samba KCC for 4.5

[Garming Sam]

Hi,

I propose that we should enable the python samba KCC for 4.5. For any
reasonably sized domain, the fully connected topology where every DC
talks to every DC causes quite a big performance hit. One domain we
encountered which uses the new KCC, appeared to have large replication
pulses when just a lone DC was introduced briefly with the old KCC and
subsequently crippled the domain. The new KCC, unlike the old one
actually obeys site link restrictions and most of the improvement comes
from the intersite replication code I wrote when I worked on this
originally.

We're still aware of shortcomings and are hoping to do a bit more work
to possibly address some of them or at least investigate them, but many
of those cases are when DCs are down or missing or when links slowly
accumulate over time. In the case of link accumulation, it would still
take a long time before it got as worse as the original KCC however and
it should be easily fixed by wiping all connections from the domain and
rebuilding from scratch. The trouble is not the fear of over-connecting
domains, but under-connecting them and failing to get replication
changes to everybody. So far, the domains we have observed have failed
to demonstrate any noticeable issues and we know of people running it
without any major issues.

In domains where it might fail to work, at worst they can turn on the
old KCC and get the old replication topology. But for larger domains, it
seems a necessary change, and even an accidental mix of the two KCC can
do some real damage.


Cheers,

Garming
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