[NOD-255] When adding orphans during netsync process - report only to debug log, unless number of orphans > k*2 (#357)

* [NOD-255] When orphan blocks arrive from netsync - don't write log unless we are in Debug

* [NOD-255] If there are more than K*2 orphans in pool - report as a potential problem anyway

* [NOD-255] Update comment to explain the K*2 figure

blockdag/process.go

@@ -37,6 +37,10 @@ const (
 	// in the future, just finished the delay
 	BFAfterDelay
 
+	// BFIsSync may be set to indicate that the block was sent as part of the
+	// netsync process
+	BFIsSync
+
 	// BFNone is a convenience value to specifically indicate no flags.
 	BFNone BehaviorFlags = 0
 )
@@ -189,7 +193,18 @@ func (dag *BlockDAG) ProcessBlock(block *util.Block, flags BehaviorFlags) (isOrp
 	}
 
 	if !allParentsExist {
-		log.Infof("Adding orphan block %s", blockHash)
+		// Some orphans during netsync are a normal part of the process, since the anticone
+		// of the chain-split is never explicitly requested.
+		// Therefore, if we are during netsync - don't report orphans to default logs.
+		//
+		// The number K*2 was chosen since in peace times anticone is limited to K blocks,
+		// while some red block can make it a bit bigger, but much more than that indicates
+		// there might be some problem with the netsync process.
+		if flags&BFIsSync == BFIsSync && uint32(len(dag.orphans)) < dag.dagParams.K*2 {
+			log.Debugf("Adding orphan block %s. This is normal part of netsync process", blockHash)
+		} else {
+			log.Infof("Adding orphan block %s", blockHash)
+		}
 		dag.addOrphanBlock(block)
 
 		return true, 0, nil

netsync/manager.go

@@ -552,6 +552,9 @@ func (sm *SyncManager) handleBlockMsg(bmsg *blockMsg) {
 	if bmsg.isDelayedBlock {
 		behaviorFlags |= blockdag.BFAfterDelay
 	}
+	if bmsg.peer == sm.syncPeer {
+		behaviorFlags |= blockdag.BFIsSync
+	}
 
 	// Process the block to include validation, orphan handling, etc.
 	isOrphan, delay, err := sm.dag.ProcessBlock(bmsg.block, behaviorFlags)