tx throttler: remove unused topology watchers (#14412)

Signed-off-by: deepthi <deepthi@planetscale.com>

changelog/19.0/19.0.0/summary.md

@@ -12,6 +12,7 @@
 ### <a id="deprecations-and-deletions"/>Deprecations and Deletions
 
 - The `MYSQL_FLAVOR` environment variable is now removed from all Docker Images.
+- VTTablet metrics for TxThrottler's topology watchers have been deprecated. They will be deleted in the next release.
 
 ### <a id="docker"/>Docker
 

go/vt/discovery/replicationlag.go

@@ -111,13 +111,13 @@ func SetMinNumTablets(numTablets int) {
 	minNumTablets.Set(numTablets)
 }
 
-// IsReplicationLagHigh verifies that the given LegacytabletHealth refers to a tablet with high
+// IsReplicationLagHigh verifies that the given TabletHealth refers to a tablet with high
 // replication lag, i.e. higher than the configured discovery_low_replication_lag flag.
 func IsReplicationLagHigh(tabletHealth *TabletHealth) bool {
 	return float64(tabletHealth.Stats.ReplicationLagSeconds) > lowReplicationLag.Get().Seconds()
 }
 
-// IsReplicationLagVeryHigh verifies that the given LegacytabletHealth refers to a tablet with very high
+// IsReplicationLagVeryHigh verifies that the given TabletHealth refers to a tablet with very high
 // replication lag, i.e. higher than the configured discovery_high_replication_lag_minimum_serving flag.
 func IsReplicationLagVeryHigh(tabletHealth *TabletHealth) bool {
 	return float64(tabletHealth.Stats.ReplicationLagSeconds) > highReplicationLagMinServing.Get().Seconds()
@@ -153,7 +153,7 @@ func FilterStatsByReplicationLag(tabletHealthList []*TabletHealth) []*TabletHeal
 		return filterStatsByLag(tabletHealthList)
 	}
 	res := filterStatsByLagWithLegacyAlgorithm(tabletHealthList)
-	// run the filter again if exactly one tablet is removed,
+	// Run the filter again if exactly one tablet is removed,
 	// and we have spare tablets.
 	if len(res) > minNumTablets.Get() && len(res) == len(tabletHealthList)-1 {
 		res = filterStatsByLagWithLegacyAlgorithm(res)
@@ -164,12 +164,12 @@ func FilterStatsByReplicationLag(tabletHealthList []*TabletHealth) []*TabletHeal
 
 func filterStatsByLag(tabletHealthList []*TabletHealth) []*TabletHealth {
 	list := make([]tabletLagSnapshot, 0, len(tabletHealthList))
-	// filter non-serving tablets and those with very high replication lag
+	// Filter out non-serving tablets and those with very high replication lag.
 	for _, ts := range tabletHealthList {
 		if !ts.Serving || ts.LastError != nil || ts.Stats == nil || IsReplicationLagVeryHigh(ts) {
 			continue
 		}
-		// Pull the current replication lag for a stable sort later.
+		// Save the current replication lag for a stable sort later.
 		list = append(list, tabletLagSnapshot{
 			ts:     ts,
 			replag: ts.Stats.ReplicationLagSeconds})
@@ -178,7 +178,7 @@ func filterStatsByLag(tabletHealthList []*TabletHealth) []*TabletHealth {
 	// Sort by replication lag.
 	sort.Sort(tabletLagSnapshotList(list))
 
-	// Pick those with low replication lag, but at least minNumTablets tablets regardless.
+	// Pick tablets with low replication lag, but at least minNumTablets tablets regardless.
 	res := make([]*TabletHealth, 0, len(list))
 	for i := 0; i < len(list); i++ {
 		if !IsReplicationLagHigh(list[i].ts) || i < minNumTablets.Get() {
@@ -190,7 +190,7 @@ func filterStatsByLag(tabletHealthList []*TabletHealth) []*TabletHealth {
 
 func filterStatsByLagWithLegacyAlgorithm(tabletHealthList []*TabletHealth) []*TabletHealth {
 	list := make([]*TabletHealth, 0, len(tabletHealthList))
-	// filter non-serving tablets
+	// Filter out non-serving tablets.
 	for _, ts := range tabletHealthList {
 		if !ts.Serving || ts.LastError != nil || ts.Stats == nil {
 			continue
@@ -200,7 +200,7 @@ func filterStatsByLagWithLegacyAlgorithm(tabletHealthList []*TabletHealth) []*Ta
 	if len(list) <= 1 {
 		return list
 	}
-	// if all have low replication lag (<=30s), return all tablets.
+	// If all tablets have low replication lag (<=30s), return all of them.
 	allLowLag := true
 	for _, ts := range list {
 		if IsReplicationLagHigh(ts) {
@@ -211,12 +211,12 @@ func filterStatsByLagWithLegacyAlgorithm(tabletHealthList []*TabletHealth) []*Ta
 	if allLowLag {
 		return list
 	}
-	// filter those affecting "mean" lag significantly
-	// calculate mean for all tablets
+	// We want to filter out tablets that are affecting "mean" lag significantly.
+	// We first calculate the mean across all tablets.
 	res := make([]*TabletHealth, 0, len(list))
 	m, _ := mean(list, -1)
 	for i, ts := range list {
-		// calculate mean by excluding ith tablet
+		// Now we calculate the mean by excluding ith tablet
 		mi, _ := mean(list, i)
 		if float64(mi) > float64(m)*0.7 {
 			res = append(res, ts)
@@ -225,9 +225,11 @@ func filterStatsByLagWithLegacyAlgorithm(tabletHealthList []*TabletHealth) []*Ta
 	if len(res) >= minNumTablets.Get() {
 		return res
 	}
-	// return at least minNumTablets tablets to avoid over loading,
-	// if there is enough tablets with replication lag < highReplicationLagMinServing.
-	// Pull the current replication lag for a stable sort.
+
+	// We want to return at least minNumTablets tablets to avoid overloading,
+	// as long as there are enough tablets with replication lag < highReplicationLagMinServing.
+
+	// Save the current replication lag for a stable sort.
 	snapshots := make([]tabletLagSnapshot, 0, len(list))
 	for _, ts := range list {
 		if !IsReplicationLagVeryHigh(ts) {

go/vt/discovery/topology_watcher.go

@@ -53,15 +53,15 @@ var (
 		"Operation", topologyWatcherOpListTablets, topologyWatcherOpGetTablet)
 )
 
-// tabletInfo is used internally by the TopologyWatcher class
+// tabletInfo is used internally by the TopologyWatcher struct.
 type tabletInfo struct {
 	alias  string
 	tablet *topodata.Tablet
 }
 
-// TopologyWatcher polls tablet from a configurable set of tablets
-// periodically. When tablets are added / removed, it calls
-// the LegacyTabletRecorder AddTablet / RemoveTablet interface appropriately.
+// TopologyWatcher polls the topology periodically for changes to
+// the set of tablets. When tablets are added / removed / modified,
+// it calls the AddTablet / RemoveTablet interface appropriately.
 type TopologyWatcher struct {
 	// set at construction time
 	topoServer          *topo.Server
@@ -79,20 +79,21 @@ type TopologyWatcher struct {
 
 	// mu protects all variables below
 	mu sync.Mutex
-	// tablets contains a map of alias -> tabletInfo for all known tablets
+	// tablets contains a map of alias -> tabletInfo for all known tablets.
 	tablets map[string]*tabletInfo
-	// topoChecksum stores a crc32 of the tablets map and is exported as a metric
+	// topoChecksum stores a crc32 of the tablets map and is exported as a metric.
 	topoChecksum uint32
-	// lastRefresh records the timestamp of the last topo refresh
+	// lastRefresh records the timestamp of the last refresh of the topology.
 	lastRefresh time.Time
-	// firstLoadDone is true when first load of the topology data is done.
+	// firstLoadDone is true when the initial load of the topology data is complete.
 	firstLoadDone bool
-	// firstLoadChan is closed when the initial loading of topology data is done.
+	// firstLoadChan is closed when the initial load of topology data is complete.
 	firstLoadChan chan struct{}
 }
 
 // NewTopologyWatcher returns a TopologyWatcher that monitors all
-// the tablets in a cell, and starts refreshing.
+// the tablets that it is configured to watch, and reloads them periodically if needed.
+// As of now there is only one implementation: watch all tablets in a cell.
 func NewTopologyWatcher(ctx context.Context, topoServer *topo.Server, hc HealthCheck, filter TabletFilter, cell string, refreshInterval time.Duration, refreshKnownTablets bool, topoReadConcurrency int, getTablets func(tw *TopologyWatcher) ([]*topodata.TabletAlias, error)) *TopologyWatcher {
 	tw := &TopologyWatcher{
 		topoServer:          topoServer,
@@ -114,14 +115,14 @@ func NewTopologyWatcher(ctx context.Context, topoServer *topo.Server, hc HealthC
 }
 
 // NewCellTabletsWatcher returns a TopologyWatcher that monitors all
-// the tablets in a cell, and starts refreshing.
+// the tablets in a cell, and reloads them as needed.
 func NewCellTabletsWatcher(ctx context.Context, topoServer *topo.Server, hc HealthCheck, f TabletFilter, cell string, refreshInterval time.Duration, refreshKnownTablets bool, topoReadConcurrency int) *TopologyWatcher {
 	return NewTopologyWatcher(ctx, topoServer, hc, f, cell, refreshInterval, refreshKnownTablets, topoReadConcurrency, func(tw *TopologyWatcher) ([]*topodata.TabletAlias, error) {
 		return tw.topoServer.GetTabletAliasesByCell(ctx, tw.cell)
 	})
 }
 
-// Start starts the topology watcher
+// Start starts the topology watcher.
 func (tw *TopologyWatcher) Start() {
 	tw.wg.Add(1)
 	go func(t *TopologyWatcher) {
@@ -140,7 +141,7 @@ func (tw *TopologyWatcher) Start() {
 	}(tw)
 }
 
-// Stop stops the watcher. It does not clean up the tablets added to LegacyTabletRecorder.
+// Stop stops the watcher. It does not clean up the tablets added to HealthCheck.
 func (tw *TopologyWatcher) Stop() {
 	tw.cancelFunc()
 	// wait for watch goroutine to finish.
@@ -151,7 +152,7 @@ func (tw *TopologyWatcher) loadTablets() {
 	var wg sync.WaitGroup
 	newTablets := make(map[string]*tabletInfo)
 
-	// first get the list of relevant tabletAliases
+	// First get the list of relevant tabletAliases.
 	tabletAliases, err := tw.getTablets(tw)
 	topologyWatcherOperations.Add(topologyWatcherOpListTablets, 1)
 	if err != nil {
@@ -166,7 +167,7 @@ func (tw *TopologyWatcher) loadTablets() {
 	}
 
 	// Accumulate a list of all known alias strings to use later
-	// when sorting
+	// when sorting.
 	tabletAliasStrs := make([]string, 0, len(tabletAliases))
 
 	tw.mu.Lock()
@@ -175,7 +176,7 @@ func (tw *TopologyWatcher) loadTablets() {
 		tabletAliasStrs = append(tabletAliasStrs, aliasStr)
 
 		if !tw.refreshKnownTablets {
-			// we already have a tabletInfo for this and the flag tells us to not refresh
+			// We already have a tabletInfo for this and the flag tells us to not refresh.
 			if val, ok := tw.tablets[aliasStr]; ok {
 				newTablets[aliasStr] = val
 				continue
@@ -188,7 +189,7 @@ func (tw *TopologyWatcher) loadTablets() {
 			tw.sem <- 1 // Wait for active queue to drain.
 			tablet, err := tw.topoServer.GetTablet(tw.ctx, alias)
 			topologyWatcherOperations.Add(topologyWatcherOpGetTablet, 1)
-			<-tw.sem // Done; enable next request to run
+			<-tw.sem // Done; enable next request to run.
 			if err != nil {
 				topologyWatcherErrors.Add(topologyWatcherOpGetTablet, 1)
 				select {
@@ -218,7 +219,7 @@ func (tw *TopologyWatcher) loadTablets() {
 			continue
 		}
 
-		// trust the alias from topo and add it if it doesn't exist
+		// Trust the alias from topo and add it if it doesn't exist.
 		if val, ok := tw.tablets[alias]; ok {
 			// check if the host and port have changed. If yes, replace tablet.
 			oldKey := TabletToMapKey(val.tablet)
@@ -230,7 +231,7 @@ func (tw *TopologyWatcher) loadTablets() {
 				topologyWatcherOperations.Add(topologyWatcherOpReplaceTablet, 1)
 			}
 		} else {
-			// This is a new tablet record, let's add it to the healthcheck
+			// This is a new tablet record, let's add it to the HealthCheck.
 			tw.healthcheck.AddTablet(newVal.tablet)
 			topologyWatcherOperations.Add(topologyWatcherOpAddTablet, 1)
 		}
@@ -252,8 +253,8 @@ func (tw *TopologyWatcher) loadTablets() {
 		close(tw.firstLoadChan)
 	}
 
-	// iterate through the tablets in a stable order and compute a
-	// checksum of the tablet map
+	// Iterate through the tablets in a stable order and compute a
+	// checksum of the tablet map.
 	sort.Strings(tabletAliasStrs)
 	var buf bytes.Buffer
 	for _, alias := range tabletAliasStrs {
@@ -269,15 +270,15 @@ func (tw *TopologyWatcher) loadTablets() {
 
 }
 
-// RefreshLag returns the time since the last refresh
+// RefreshLag returns the time since the last refresh.
 func (tw *TopologyWatcher) RefreshLag() time.Duration {
 	tw.mu.Lock()
 	defer tw.mu.Unlock()
 
 	return time.Since(tw.lastRefresh)
 }
 
-// TopoChecksum returns the checksum of the current state of the topo
+// TopoChecksum returns the checksum of the current state of the topo.
 func (tw *TopologyWatcher) TopoChecksum() uint32 {
 	tw.mu.Lock()
 	defer tw.mu.Unlock()
@@ -286,7 +287,7 @@ func (tw *TopologyWatcher) TopoChecksum() uint32 {
 }
 
 // TabletFilter is an interface that can be given to a TopologyWatcher
-// to be applied as an additional filter on the list of tablets returned by its getTablets function
+// to be applied as an additional filter on the list of tablets returned by its getTablets function.
 type TabletFilter interface {
 	// IsIncluded returns whether tablet is included in this filter
 	IsIncluded(tablet *topodata.Tablet) bool
@@ -300,18 +301,18 @@ type FilterByShard struct {
 }
 
 // filterShard describes a filter for a given shard or keyrange inside
-// a keyspace
+// a keyspace.
 type filterShard struct {
 	keyspace string
 	shard    string
 	keyRange *topodata.KeyRange // only set if shard is also a KeyRange
 }
 
-// NewFilterByShard creates a new FilterByShard on top of an existing
-// LegacyTabletRecorder. Each filter is a keyspace|shard entry, where shard
+// NewFilterByShard creates a new FilterByShard for use by a
+// TopologyWatcher. Each filter is a keyspace|shard entry, where shard
 // can either be a shard name, or a keyrange. All tablets that match
-// at least one keyspace|shard tuple will be forwarded to the
-// underlying LegacyTabletRecorder.
+// at least one keyspace|shard tuple will be forwarded by the
+// TopologyWatcher to its consumer.
 func NewFilterByShard(filters []string) (*FilterByShard, error) {
 	m := make(map[string][]*filterShard)
 	for _, filter := range filters {
@@ -348,8 +349,7 @@ func NewFilterByShard(filters []string) (*FilterByShard, error) {
 	}, nil
 }
 
-// IsIncluded returns true iff the tablet's keyspace and shard should be
-// forwarded to the underlying LegacyTabletRecorder.
+// IsIncluded returns true iff the tablet's keyspace and shard match what we have.
 func (fbs *FilterByShard) IsIncluded(tablet *topodata.Tablet) bool {
 	canonical, kr, err := topo.ValidateShardName(tablet.Shard)
 	if err != nil {
@@ -370,15 +370,14 @@ func (fbs *FilterByShard) IsIncluded(tablet *topodata.Tablet) bool {
 	return false
 }
 
-// FilterByKeyspace is a filter that filters tablets by
-// keyspace
+// FilterByKeyspace is a filter that filters tablets by keyspace.
 type FilterByKeyspace struct {
 	keyspaces map[string]bool
 }
 
 // NewFilterByKeyspace creates a new FilterByKeyspace.
 // Each filter is a keyspace entry. All tablets that match
-// a keyspace will be forwarded to the underlying LegacyTabletRecorder.
+// a keyspace will be forwarded to the TopologyWatcher's consumer.
 func NewFilterByKeyspace(selectedKeyspaces []string) *FilterByKeyspace {
 	m := make(map[string]bool)
 	for _, keyspace := range selectedKeyspaces {
@@ -390,8 +389,7 @@ func NewFilterByKeyspace(selectedKeyspaces []string) *FilterByKeyspace {
 	}
 }
 
-// IsIncluded returns true if the tablet's keyspace should be
-// forwarded to the underlying LegacyTabletRecorder.
+// IsIncluded returns true if the tablet's keyspace matches what we have.
 func (fbk *FilterByKeyspace) IsIncluded(tablet *topodata.Tablet) bool {
 	_, exist := fbk.keyspaces[tablet.Keyspace]
 	return exist