eth/downloader: change intial download size (#21366)

This changes how the downloader works, a little bit. Previously, when block sync started,
we immediately started filling up to 8192 blocks. Usually this is fine, blocks are small
in the early numbers. The threshold then is lowered as we measure the size of the blocks
that are filled.

However, if the node is shut down and restarts syncing while we're in a heavy segment,
that might be bad. This PR introduces a more conservative initial threshold of 2K blocks
instead.

eth/downloader/downloader.go

@@ -219,7 +219,7 @@ func New(checkpoint uint64, stateDb ethdb.Database, stateBloom *trie.SyncBloom,
 		stateBloom:     stateBloom,
 		mux:            mux,
 		checkpoint:     checkpoint,
-		queue:          newQueue(blockCacheItems),
+		queue:          newQueue(blockCacheMaxItems, blockCacheInitialItems),
 		peers:          newPeerSet(),
 		rttEstimate:    uint64(rttMaxEstimate),
 		rttConfidence:  uint64(1000000),
@@ -379,7 +379,7 @@ func (d *Downloader) synchronise(id string, hash common.Hash, td *big.Int, mode
 		d.stateBloom.Close()
 	}
 	// Reset the queue, peer set and wake channels to clean any internal leftover state
-	d.queue.Reset(blockCacheItems)
+	d.queue.Reset(blockCacheMaxItems, blockCacheInitialItems)
 	d.peers.Reset()
 
 	for _, ch := range []chan bool{d.bodyWakeCh, d.receiptWakeCh} {

eth/downloader/downloader_test.go

@@ -39,7 +39,7 @@ import (
 func init() {
 	fullMaxForkAncestry = 10000
 	lightMaxForkAncestry = 10000
-	blockCacheItems = 1024
+	blockCacheMaxItems = 1024
 	fsHeaderContCheck = 500 * time.Millisecond
 }
 
@@ -544,7 +544,7 @@ func testCanonicalSynchronisation(t *testing.T, protocol int, mode SyncMode) {
 	defer tester.terminate()
 
 	// Create a small enough block chain to download
-	chain := testChainBase.shorten(blockCacheItems - 15)
+	chain := testChainBase.shorten(blockCacheMaxItems - 15)
 	tester.newPeer("peer", protocol, chain)
 
 	// Synchronise with the peer and make sure all relevant data was retrieved
@@ -607,8 +607,8 @@ func testThrottling(t *testing.T, protocol int, mode SyncMode) {
 			}
 			tester.lock.Unlock()
 
-			if cached == blockCacheItems ||
-				cached == blockCacheItems-reorgProtHeaderDelay ||
+			if cached == blockCacheMaxItems ||
+				cached == blockCacheMaxItems-reorgProtHeaderDelay ||
 				retrieved+cached+frozen == targetBlocks+1 ||
 				retrieved+cached+frozen == targetBlocks+1-reorgProtHeaderDelay {
 				break
@@ -619,8 +619,8 @@ func testThrottling(t *testing.T, protocol int, mode SyncMode) {
 		tester.lock.RLock()
 		retrieved = len(tester.ownBlocks)
 		tester.lock.RUnlock()
-		if cached != blockCacheItems && cached != blockCacheItems-reorgProtHeaderDelay && retrieved+cached+frozen != targetBlocks+1 && retrieved+cached+frozen != targetBlocks+1-reorgProtHeaderDelay {
-			t.Fatalf("block count mismatch: have %v, want %v (owned %v, blocked %v, target %v)", cached, blockCacheItems, retrieved, frozen, targetBlocks+1)
+		if cached != blockCacheMaxItems && cached != blockCacheMaxItems-reorgProtHeaderDelay && retrieved+cached+frozen != targetBlocks+1 && retrieved+cached+frozen != targetBlocks+1-reorgProtHeaderDelay {
+			t.Fatalf("block count mismatch: have %v, want %v (owned %v, blocked %v, target %v)", cached, blockCacheMaxItems, retrieved, frozen, targetBlocks+1)
 		}
 
 		// Permit the blocked blocks to import
@@ -873,7 +873,7 @@ func testMultiProtoSync(t *testing.T, protocol int, mode SyncMode) {
 	defer tester.terminate()
 
 	// Create a small enough block chain to download
-	chain := testChainBase.shorten(blockCacheItems - 15)
+	chain := testChainBase.shorten(blockCacheMaxItems - 15)
 
 	// Create peers of every type
 	tester.newPeer("peer 63", 63, chain)
@@ -965,7 +965,7 @@ func testMissingHeaderAttack(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	chain := testChainBase.shorten(blockCacheItems - 15)
+	chain := testChainBase.shorten(blockCacheMaxItems - 15)
 	brokenChain := chain.shorten(chain.len())
 	delete(brokenChain.headerm, brokenChain.chain[brokenChain.len()/2])
 	tester.newPeer("attack", protocol, brokenChain)
@@ -997,7 +997,7 @@ func testShiftedHeaderAttack(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	chain := testChainBase.shorten(blockCacheItems - 15)
+	chain := testChainBase.shorten(blockCacheMaxItems - 15)
 
 	// Attempt a full sync with an attacker feeding shifted headers
 	brokenChain := chain.shorten(chain.len())
@@ -1202,7 +1202,7 @@ func testSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 
 	tester := newTester()
 	defer tester.terminate()
-	chain := testChainBase.shorten(blockCacheItems - 15)
+	chain := testChainBase.shorten(blockCacheMaxItems - 15)
 
 	// Set a sync init hook to catch progress changes
 	starting := make(chan struct{})
@@ -1362,7 +1362,7 @@ func testFailedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 
 	tester := newTester()
 	defer tester.terminate()
-	chain := testChainBase.shorten(blockCacheItems - 15)
+	chain := testChainBase.shorten(blockCacheMaxItems - 15)
 
 	// Set a sync init hook to catch progress changes
 	starting := make(chan struct{})
@@ -1435,7 +1435,7 @@ func testFakedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 
 	tester := newTester()
 	defer tester.terminate()
-	chain := testChainBase.shorten(blockCacheItems - 15)
+	chain := testChainBase.shorten(blockCacheMaxItems - 15)
 
 	// Set a sync init hook to catch progress changes
 	starting := make(chan struct{})

eth/downloader/queue.go

@@ -40,9 +40,10 @@ const (
 )
 
 var (
-	blockCacheItems      = 8192             // Maximum number of blocks to cache before throttling the download
-	blockCacheMemory     = 64 * 1024 * 1024 // Maximum amount of memory to use for block caching
-	blockCacheSizeWeight = 0.1              // Multiplier to approximate the average block size based on past ones
+	blockCacheMaxItems     = 8192             // Maximum number of blocks to cache before throttling the download
+	blockCacheInitialItems = 2048             // Initial number of blocks to start fetching, before we know the sizes of the blocks
+	blockCacheMemory       = 64 * 1024 * 1024 // Maximum amount of memory to use for block caching
+	blockCacheSizeWeight   = 0.1              // Multiplier to approximate the average block size based on past ones
 )
 
 var (
@@ -142,7 +143,7 @@ type queue struct {
 }
 
 // newQueue creates a new download queue for scheduling block retrieval.
-func newQueue(blockCacheLimit int) *queue {
+func newQueue(blockCacheLimit int, thresholdInitialSize int) *queue {
 	lock := new(sync.RWMutex)
 	q := &queue{
 		headerContCh:     make(chan bool),
@@ -151,12 +152,12 @@ func newQueue(blockCacheLimit int) *queue {
 		active:           sync.NewCond(lock),
 		lock:             lock,
 	}
-	q.Reset(blockCacheLimit)
+	q.Reset(blockCacheLimit, thresholdInitialSize)
 	return q
 }
 
 // Reset clears out the queue contents.
-func (q *queue) Reset(blockCacheLimit int) {
+func (q *queue) Reset(blockCacheLimit int, thresholdInitialSize int) {
 	q.lock.Lock()
 	defer q.lock.Unlock()
 
@@ -175,6 +176,7 @@ func (q *queue) Reset(blockCacheLimit int) {
 	q.receiptPendPool = make(map[string]*fetchRequest)
 
 	q.resultCache = newResultStore(blockCacheLimit)
+	q.resultCache.SetThrottleThreshold(uint64(thresholdInitialSize))
 }
 
 // Close marks the end of the sync, unblocking Results.

eth/downloader/queue_test.go

@@ -97,7 +97,7 @@ func dummyPeer(id string) *peerConnection {
 }
 
 func TestBasics(t *testing.T) {
-	q := newQueue(10)
+	q := newQueue(10, 10)
 	if !q.Idle() {
 		t.Errorf("new queue should be idle")
 	}
@@ -174,7 +174,7 @@ func TestBasics(t *testing.T) {
 }
 
 func TestEmptyBlocks(t *testing.T) {
-	q := newQueue(10)
+	q := newQueue(10, 10)
 
 	q.Prepare(1, FastSync)
 	// Schedule a batch of headers
@@ -244,7 +244,7 @@ func XTestDelivery(t *testing.T) {
 		log.Root().SetHandler(log.StdoutHandler)
 
 	}
-	q := newQueue(10)
+	q := newQueue(10, 10)
 	var wg sync.WaitGroup
 	q.Prepare(1, FastSync)
 	wg.Add(1)

eth/downloader/testchain_test.go

@@ -39,7 +39,7 @@ var (
 )
 
 // The common prefix of all test chains:
-var testChainBase = newTestChain(blockCacheItems+200, testGenesis)
+var testChainBase = newTestChain(blockCacheMaxItems+200, testGenesis)
 
 // Different forks on top of the base chain:
 var testChainForkLightA, testChainForkLightB, testChainForkHeavy *testChain