This change provides a efficient way of replication
between regions of a global distributed cluster.
This approach makes object-replicator to push replicas
to a primary node in a remote region, then, to skip
pushing them to next primary node in the region with
expecting asynchronous replication.
This implementation includes a couple of changes on
ssync_sender to allow object-replicator to delete local
handoff objects correctly. One is to return a list of existing
objects in remote region. The list includes local paths of the
objects which exist both on the local device and the remote device.
The other is supporting existence check for specified objects.
It requires the object list build by the first change. When
the object list is given, ssync_sender does only missing_check
based on the list. These changes are needed because current
swift can not handle the existence check in object-level.
Note that this feature will work partially (i.e. only when
primary-to-primary) with rsync.
Implements: blueprint efficient-replication
Change-Id: I5d990444d7977f4127bb37f9256212c893438df1
20ca279d74