void synchronizeIfNotScheduled(DistributedRegion region,
        InternalDistributedMember lostMember, VersionSource lostVersionSource) {
      if (region.setRegionSynchronizedWithIfNotScheduled(lostVersionSource)) {
        // if region synchronization has not been scheduled or performed,
        // we do synchronization with no delay as we received the synchronization request
        // indicating timed task has been triggered on other nodes
        if (logger.isDebugEnabled()) {
          logger.debug("Newly joined member is triggered to schedule SynchronizeForLostMember");
        }
        region.scheduleSynchronizeForLostMember(lostMember, lostVersionSource, 0);
      } else {
        if (logger.isDebugEnabled()) {
          logger.debug(
              "Live member has been scheduled SynchronizeForLostMember by membership listener.");
        }
      }
    }
If there is no region sync scheduled after checking region version holder holding the
lost member. Region sync requests are sent to members hosting the region.
This is only executed when processing region sync requests from other members hosting the
region.
Region sync is triggered by a member departed event. If this member exists during the
event, region sync would be scheduled. This method is only handles the case when
node is recently joining the cluster or restarted, and does not get the member departed
event.
geode-core/src/main/java/org/apache/geode/internal/cache/InitialImageOperation.java