Make simulation use a transition matrix for block size

This enables simulating periods of high load, and periods of low to no load.
(low load because future ops will still terminate in that time frame)

PENDING.md

@@ -37,6 +37,7 @@ IMPROVEMENTS
 
 * SDK
  - #2573 [x/distribution] add accum invariance
+ - \#1924 [simulation] Use a transition matrix for block size
 
 * Tendermint
 

client/lcd/certificates.go

@@ -43,7 +43,7 @@ func generateSelfSignedCert(host string) (certBytes []byte, priv *ecdsa.PrivateK
 		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
 		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
 		BasicConstraintsValid: true,
-		IsCA:                  true,
+		IsCA: true,
 	}
 	hosts := strings.Split(host, ",")
 	for _, h := range hosts {

x/mock/simulation/constants.go

@@ -28,4 +28,10 @@ var (
 		{10, 50, 5},
 		{0, 10, 1000},
 	})
+	// 3 states: rand in range [0, 4*provided blocksize], rand in range [0, 2 * provided blocksize], 0
+	blockSizeTransitionMatrix, _ = CreateTransitionMatrix([][]int{
+		{85, 5, 0},
+		{15, 92, 1},
+		{0, 3, 99},
+	})
 )

x/mock/simulation/random_simulate_blocks.go

@@ -108,7 +108,7 @@ func SimulateFromSeed(tb testing.TB, app *baseapp.BaseApp,
 		blockLogBuilders = make([]*strings.Builder, numBlocks)
 	}
 	displayLogs := logPrinter(testingMode, blockLogBuilders)
-	blockSimulator := createBlockSimulator(testingMode, tb, t, event, invariants, ops, operationQueue, timeOperationQueue, numBlocks, displayLogs)
+	blockSimulator := createBlockSimulator(testingMode, tb, t, event, invariants, ops, operationQueue, timeOperationQueue, numBlocks, blockSize, displayLogs)
 	if !testingMode {
 		b.ResetTimer()
 	} else {
@@ -142,7 +142,6 @@ func SimulateFromSeed(tb testing.TB, app *baseapp.BaseApp,
 		}
 
 		ctx := app.NewContext(false, header)
-		thisBlockSize := getBlockSize(r, blockSize)
 
 		// Run queued operations. Ignores blocksize if blocksize is too small
 		logWriter("Queued operations")
@@ -153,9 +152,8 @@ func SimulateFromSeed(tb testing.TB, app *baseapp.BaseApp,
 			assertAllInvariants(t, app, header, invariants, "QueuedOperations", displayLogs)
 		}
 
-		thisBlockSize = thisBlockSize - numQueuedOpsRan - numQueuedTimeOpsRan
 		logWriter("Standard operations")
-		operations := blockSimulator(thisBlockSize, r, app, ctx, accs, header, logWriter)
+		operations := blockSimulator(r, app, ctx, accs, header, logWriter)
 		opCount += operations + numQueuedOpsRan + numQueuedTimeOpsRan
 		if testingMode {
 			// Make sure invariants hold at end of block
@@ -200,9 +198,14 @@ func SimulateFromSeed(tb testing.TB, app *baseapp.BaseApp,
 
 // Returns a function to simulate blocks. Written like this to avoid constant parameters being passed everytime, to minimize
 // memory overhead
-func createBlockSimulator(testingMode bool, tb testing.TB, t *testing.T, event func(string), invariants []Invariant, ops []WeightedOperation, operationQueue map[int][]Operation, timeOperationQueue []FutureOperation, totalNumBlocks int, displayLogs func()) func(
-	blocksize int, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, accounts []Account, header abci.Header, logWriter func(string)) (opCount int) {
-	totalOpWeight := 0
+func createBlockSimulator(testingMode bool, tb testing.TB, t *testing.T, event func(string), invariants []Invariant, ops []WeightedOperation, operationQueue map[int][]Operation, timeOperationQueue []FutureOperation, totalNumBlocks int, avgBlockSize int, displayLogs func()) func(
+	r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, accounts []Account, header abci.Header, logWriter func(string)) (opCount int) {
+	var (
+		lastBlocksizeState = 0 // state for [4 * uniform distribution]
+		totalOpWeight      = 0
+		blocksize          int
+	)
+
 	for i := 0; i < len(ops); i++ {
 		totalOpWeight += ops[i].Weight
 	}
@@ -217,8 +220,10 @@ func createBlockSimulator(testingMode bool, tb testing.TB, t *testing.T, event f
 		// shouldn't happen
 		return ops[0].Op
 	}
-	return func(blocksize int, r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context,
+
+	return func(r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context,
 		accounts []Account, header abci.Header, logWriter func(string)) (opCount int) {
+		lastBlocksizeState, blocksize = getBlockSize(r, lastBlocksizeState, avgBlockSize)
 		for j := 0; j < blocksize; j++ {
 			logUpdate, futureOps, err := selectOp(r)(r, app, ctx, accounts, event)
 			if err != nil {
@@ -253,16 +258,18 @@ func getTestingMode(tb testing.TB) (testingMode bool, t *testing.T, b *testing.B
 	return
 }
 
-func getBlockSize(r *rand.Rand, blockSize int) int {
-	load := r.Float64()
-	switch {
-	case load < 0.33:
-		return 0
-	case load < 0.66:
-		return r.Intn(blockSize * 2)
-	default:
-		return r.Intn(blockSize * 4)
+func getBlockSize(r *rand.Rand, lastBlockSizeState, avgBlockSize int) (state, blocksize int) {
+	// TODO: Make blockSizeTransitionMatrix non-global
+	// TODO: Make default blocksize transitition matrix actually make the average blocksize equal to avgBlockSize
+	state = blockSizeTransitionMatrix.NextState(r, lastBlockSizeState)
+	if state == 0 {
+		blocksize = r.Intn(avgBlockSize * 4)
+	} else if state == 1 {
+		blocksize = r.Intn(avgBlockSize * 2)
+	} else {
+		blocksize = 0
 	}
+	return
 }
 
 // adds all future operations into the operation queue.