asim: refactor the code to use rebalancing snapshot rate

Previously, asim used ReplicaAddRate for SimulationSettings, which was an
artificial approximation and differed from the real cluster behaviour with
snapshot-based calculation. This patch refactors it to use the actual snapshot
rate instead. There is no behavioral change, since SnapshotRate = AddRate /
(1024*1024). So
(RangeSize/(1024*1024))/(AddRate)=RangeSize/(1024*1024*AddRate)=RangeSize/SnapshotRate.
NB: there's an existing bug here; the calculation is missing a final
multiplication by time.Second, and snapshot rate is defined per second. A future
commit will address this.

Epic: none
Release note: none

Author: wenyihu6

pkg/kv/kvserver/asim/config/settings.go

@@ -11,7 +11,7 @@ const (
 	defaultTickInteval             = 500 * time.Millisecond
 	defaultMetricsInterval         = 10 * time.Second
 	defaultReplicaChangeBaseDelay  = 100 * time.Millisecond
-	defaultReplicaAddDelayFactor   = 16
+	defaultRebalancingSnapshotRate = 16 << 20 // 16MiB/s
 	defaultSplitQueueDelay         = 100 * time.Millisecond
 	defaultRangeSizeSplitThreshold = 512 * 1024 * 1024 // 512mb
 	defaultRangeRebalanceThreshold = 0.05
@@ -56,13 +56,11 @@ type SimulationSettings struct {
 	// (add,remove). It accounts for a fixed overhead of initiating a replica
 	// movement.
 	ReplicaChangeBaseDelay time.Duration
-	// ReplicaAddRate is the factor applied to the range size (MB) when
-	// calculating how long a replica addition will take for a given range
-	// size. For adding a replica to a new store, the delay is calculated as
-	// ReplicaChangeBaseDelay + (RangeSize(MB)  * ReplicaAddRate) milliseconds.
-	// This is analogous to the rate at which a store will ingest snapshots for
-	// up replication.
-	ReplicaAddRate float64
+	// RebalancingSnapshotRate is rate at which newly added replicas will be
+	// added based on the range size. e.g., When the range size is 16MB, and the
+	// RebalancingSnapshotRate is 16 << 20, the delay for adding a replica wil be
+	// 1 second + ReplicaChangeBaseDelay.
+	RebalancingSnapshotRate int64
 	// SplitQueueDelay is the delay that range splits take to complete.
 	SplitQueueDelay time.Duration
 	// RangeSizeSplitThreshold is the threshold in MB, below which ranges will
@@ -126,7 +124,7 @@ func DefaultSimulationSettings() *SimulationSettings {
 		MetricsInterval:         defaultMetricsInterval,
 		Seed:                    defaultSeed,
 		ReplicaChangeBaseDelay:  defaultReplicaChangeBaseDelay,
-		ReplicaAddRate:          defaultReplicaAddDelayFactor,
+		RebalancingSnapshotRate: defaultRebalancingSnapshotRate,
 		SplitQueueDelay:         defaultSplitQueueDelay,
 		RangeSizeSplitThreshold: defaultRangeSizeSplitThreshold,
 		RangeRebalanceThreshold: defaultRangeRebalanceThreshold,
@@ -154,7 +152,7 @@ func (s *SimulationSettings) ReplicaChangeDelayFn() func(rangeSize int64, add bo
 	return func(rangeSize int64, add bool) time.Duration {
 		delay := s.ReplicaChangeBaseDelay
 		if add {
-			delay += (time.Duration(rangeSize/(1024*1024)) / time.Duration(s.ReplicaAddRate))
+			delay += (time.Duration(rangeSize) / time.Duration(s.RebalancingSnapshotRate))
 		}
 		return delay
 	}

pkg/kv/kvserver/asim/op/controller_test.go

@@ -141,7 +141,7 @@ func TestLeaseTransferOp(t *testing.T) {
 func TestRelocateRangeOp(t *testing.T) {
 	settings := config.DefaultSimulationSettings()
 	start := settings.StartTime
-	settings.ReplicaAddRate = 1
+	settings.RebalancingSnapshotRate = 1 << 20
 	settings.ReplicaChangeBaseDelay = 5 * time.Second
 	settings.StateExchangeInterval = 1 * time.Second
 	settings.StateExchangeDelay = 0

pkg/kv/kvserver/asim/storerebalancer/store_rebalancer_test.go

@@ -191,7 +191,7 @@ func TestStoreRebalancerBalances(t *testing.T) {
 	testingStore := state.StoreID(1)
 	testSettings := config.DefaultSimulationSettings()
 	start := testSettings.StartTime
-	testSettings.ReplicaAddRate = 1
+	testSettings.RebalancingSnapshotRate = 1 << 20
 	testSettings.ReplicaChangeBaseDelay = 1 * time.Second
 	testSettings.StateExchangeInterval = 1 * time.Second
 	testSettings.StateExchangeDelay = 0