Currently on a topology change we reset the high prepared seqno of the active node. This happens because of the code here http://src.couchbase.org/source/xref/trunk/kv_engine/engines/ep/src/durability/active_durability_monitor.cc#691-692. Believe this is also an issue if we do an active->replica/pending issue where the new passiveDM will not have a correct HPS.
Below test case is a simple reproduction.
|For Gerrit Dashboard: MB-34315|
|110103,4||MB-34315: Maintain HPS on topology change with 0 in-flight SWrites||master||kv_engine||Status: MERGED||+2||+1|