There's a general issue with using delta-sync MMR that needs some
resolution (It's causing some considerable pain for customers): It is
possible to put the entire system into endless fallbacks until a new
and/or reloaded node gets a write operation. The general problem is that
when an existing master queries the new/reloaded master's accesslog DB,
zero entries are returned. This then triggers the fallback. This happens
up util such a time as the new/reloaded master gets a direct write op.
I've worked around it in general by immediately doing a no-op on the
primary db (ldapmodify/replace an attribute value with its own value),
but it would be nice to be able to bring new MMR nodes online or be able
to reload MMR nodes for if they get out of sync, etc, without causing
this sync fallback issue. There is no clear solution at the moment on
what to do about zero results from the accesslog in the delta-sync MMR
scenario. Proposals welcome. ;)