[ECTM-104] Pivot block selection algorithm

src/it/scala/io/iohk/ethereum/sync/FastSyncItSpec.scala

@@ -64,8 +64,8 @@ class FastSyncItSpec extends FlatSpecBase with Matchers with BeforeAndAfter {
       _ <- peer1.startFastSync().delayExecution(50.milliseconds)
       _ <- peer1.waitForFastSyncFinish()
     } yield {
-      assert(peer1.bl.getBestBlockNumber() == peer2.bl.getBestBlockNumber() - peer2.testSyncConfig.targetBlockOffset)
-      assert(peer1.bl.getBestBlockNumber() == peer3.bl.getBestBlockNumber() - peer3.testSyncConfig.targetBlockOffset)
+      assert(peer1.bl.getBestBlockNumber() == peer2.bl.getBestBlockNumber() - peer2.testSyncConfig.pivotBlockOffset)
+      assert(peer1.bl.getBestBlockNumber() == peer3.bl.getBestBlockNumber() - peer3.testSyncConfig.pivotBlockOffset)
     }
   }
 
@@ -81,13 +81,13 @@ class FastSyncItSpec extends FlatSpecBase with Matchers with BeforeAndAfter {
         val trie = peer1.getBestBlockTrie()
         // due to the fact that function generating state is deterministic both peer2 and peer3 ends up with exactly same
         // state, so peer1 can get whole trie from both of them.
-        assert(peer1.bl.getBestBlockNumber() == peer2.bl.getBestBlockNumber() - peer2.testSyncConfig.targetBlockOffset)
-        assert(peer1.bl.getBestBlockNumber() == peer3.bl.getBestBlockNumber() - peer3.testSyncConfig.targetBlockOffset)
+        assert(peer1.bl.getBestBlockNumber() == peer2.bl.getBestBlockNumber() - peer2.testSyncConfig.pivotBlockOffset)
+        assert(peer1.bl.getBestBlockNumber() == peer3.bl.getBestBlockNumber() - peer3.testSyncConfig.pivotBlockOffset)
         assert(trie.isDefined)
       }
   }
 
-  it should "should update target block" in customTestCaseResourceM(FakePeer.start2FakePeersRes()) {
+  it should "should update pivot block" in customTestCaseResourceM(FakePeer.start2FakePeersRes()) {
     case (peer1, peer2) =>
       for {
         _ <- peer2.importBlocksUntil(1000)(IdentityUpdate)
@@ -96,7 +96,7 @@ class FastSyncItSpec extends FlatSpecBase with Matchers with BeforeAndAfter {
         _ <- peer1.startFastSync().delayExecution(50.milliseconds)
         _ <- peer1.waitForFastSyncFinish()
       } yield {
-        assert(peer1.bl.getBestBlockNumber() == peer2.bl.getBestBlockNumber() - peer2.testSyncConfig.targetBlockOffset)
+        assert(peer1.bl.getBestBlockNumber() == peer2.bl.getBestBlockNumber() - peer2.testSyncConfig.pivotBlockOffset)
       }
   }
 }
@@ -308,7 +308,7 @@ object FastSyncItSpec {
     lazy val validators = new MockValidatorsAlwaysSucceed
 
     val testSyncConfig = syncConfig.copy(
-      minPeersToChooseTargetBlock = 1,
+      minPeersToChoosePivotBlock = 1,
       peersScanInterval = 5.milliseconds,
       blockHeadersPerRequest = 200,
       blockBodiesPerRequest = 50,

src/main/resources/application.conf

@@ -320,12 +320,16 @@ mantis {
     # Requested number of MPT nodes when syncing from other peers
     nodes-per-request = 384
 
-    # Minimum number of peers required to start fast-sync (by determining the target block)
-    min-peers-to-choose-target-block = 2
+    # Minimum number of peers required to start fast-sync (by determining the pivot block)
+    min-peers-to-choose-pivot-block = 3
+
+    # Number of additional peers used to determine pivot block during fast-sync
+    # Number of peers used to reach consensus = min-peers-to-choose-pivot-block + peers-to-choose-pivot-block-margin
+    peers-to-choose-pivot-block-margin = 1
 
     # During fast-sync when most up to date block is determined from peers, the actual target block number
     # will be decreased by this value
-    target-block-offset = 128
+    pivot-block-offset = 128
 
     # How often to query peers for new blocks after the top of the chain has been reached
     check-for-new-block-interval = 10.seconds

src/main/scala/io/iohk/ethereum/blockchain/sync/PeerListSupport.scala

@@ -22,7 +22,12 @@ trait PeerListSupport {
 
   var handshakedPeers: PeersMap = Map.empty
 
-  scheduler.scheduleWithFixedDelay(0.seconds, syncConfig.peersScanInterval, etcPeerManager, EtcPeerManagerActor.GetHandshakedPeers)(global, context.self)
+  scheduler.scheduleWithFixedDelay(
+    0.seconds,
+    syncConfig.peersScanInterval,
+    etcPeerManager,
+    EtcPeerManagerActor.GetHandshakedPeers
+  )(global, context.self)
 
   def removePeer(peerId: PeerId): Unit = {
     peerEventBus ! Unsubscribe(PeerDisconnectedClassifier(PeerSelector.WithId(peerId)))