Remove legacy EmergencyReparentShard stats (#15941)

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

changelog/20.0/20.0.0/summary.md

@@ -9,6 +9,7 @@
     - [MySQL binaries in the vitess/lite Docker images](#vitess-lite)
     - [vitess/base and vitess/k8s Docker images](#base-k8s-images)
     - [`gh-ost` binary and endtoend tests](#gh-ost-binary-tests-removal)
+    - [Legacy `EmergencyReparentShard` stats](#legacy-emergencyshardreparent-stats)
   - **[Breaking changes](#breaking-changes)**
     - [Metric Name Changes in VTOrc](#metric-change-vtorc)
     - [ENUM and SET column handling in VTGate VStream API](#enum-set-vstream)
@@ -107,6 +108,19 @@ Vitess 20.0 drops support for `gh-ost` DDL strategy.
 
 Vitess' endtoend tests no longer use nor test `gh-ost` migrations.
 
+#### <a id="legacy-emergencyshardreparent-stats"/>Legacy `EmergencyReparentShard` stats
+
+The following `EmergencyReparentShard` stats were deprecated in Vitess 18.0 and are removed in Vitess 20.0:
+- `ers_counter`
+- `ers_success_counter`
+- `ers_failure_counter`
+
+These counters are replaced by the following stats _(introduced in Vitess 18.0)_:
+- `emergency_reparent_counts` - Number of times `EmergencyReparentShard` has been run. It is further subdivided by the keyspace, shard and the result of the operation.
+- `planned_reparent_counts` - Number of times `PlannedReparentShard` has been run. It is further subdivided by the keyspace, shard and the result of the operation.
+
+Also, the `reparent_shard_operation_timings` stat was added to provide per-operation timings of reparent operations.
+
 ### <a id="breaking-changes"/>Breaking Changes
 
 #### <a id="metric-change-vtorc"/>Metric Name Changes in VTOrc
@@ -353,4 +367,4 @@ The internal gRPC client now caches the static auth credentials and supports rel
 #### <a id="updated-node"/>vtadmin-web updated to node v20.12.2 (LTS)
 
 Building `vtadmin-web` now requires node >= v20.12.0 (LTS). Breaking changes from v18 to v20 can be found at https://nodejs.org/en/blog/release/v20.12.0 -- with no known issues that apply to VTAdmin.
-Full details on the node v20.12.2 release can be found at https://nodejs.org/en/blog/release/v20.12.2.
+Full details on the node v20.12.2 release can be found at https://nodejs.org/en/blog/release/v20.12.2.

go/vt/vtctl/reparentutil/emergency_reparenter.go

@@ -68,15 +68,8 @@ type EmergencyReparentOptions struct {
 }
 
 // counters for Emergency Reparent Shard
-var (
-	// TODO(timvaillancourt): remove legacyERS* gauges in v19+.
-	legacyERSCounter        = stats.NewGauge("ers_counter", "Number of times Emergency Reparent Shard has been run")
-	legacyERSSuccessCounter = stats.NewGauge("ers_success_counter", "Number of times Emergency Reparent Shard has succeeded")
-	legacyERSFailureCounter = stats.NewGauge("ers_failure_counter", "Number of times Emergency Reparent Shard has failed")
-
-	ersCounter = stats.NewCountersWithMultiLabels("emergency_reparent_counts", "Number of times Emergency Reparent Shard has been run",
-		[]string{"Keyspace", "Shard", "Result"},
-	)
+var ersCounter = stats.NewCountersWithMultiLabels("emergency_reparent_counts", "Number of times Emergency Reparent Shard has been run",
+	[]string{"Keyspace", "Shard", "Result"},
 )
 
 // NewEmergencyReparenter returns a new EmergencyReparenter object, ready to
@@ -125,11 +118,9 @@ func (erp *EmergencyReparenter) ReparentShard(ctx context.Context, keyspace stri
 		reparentShardOpTimings.Add("EmergencyReparentShard", time.Since(startTime))
 		switch err {
 		case nil:
-			legacyERSSuccessCounter.Add(1)
 			ersCounter.Add(append(statsLabels, successResult), 1)
 			event.DispatchUpdate(ev, "finished EmergencyReparentShard")
 		default:
-			legacyERSFailureCounter.Add(1)
 			ersCounter.Add(append(statsLabels, failureResult), 1)
 			event.DispatchUpdate(ev, "failed EmergencyReparentShard: "+err.Error())
 		}
@@ -154,7 +145,6 @@ func (erp *EmergencyReparenter) getLockAction(newPrimaryAlias *topodatapb.Tablet
 func (erp *EmergencyReparenter) reparentShardLocked(ctx context.Context, ev *events.Reparent, keyspace, shard string, opts EmergencyReparentOptions) (err error) {
 	// log the starting of the operation and increment the counter
 	erp.logger.Infof("will initiate emergency reparent shard in keyspace - %s, shard - %s", keyspace, shard)
-	legacyERSCounter.Add(1)
 
 	var (
 		stoppedReplicationSnapshot *replicationSnapshot

go/vt/vtctl/reparentutil/emergency_reparenter_test.go

@@ -2586,9 +2586,6 @@ func TestEmergencyReparenter_waitForAllRelayLogsToApply(t *testing.T) {
 
 func TestEmergencyReparenterStats(t *testing.T) {
 	ersCounter.ResetAll()
-	legacyERSCounter.Reset()
-	legacyERSSuccessCounter.Reset()
-	legacyERSFailureCounter.Reset()
 	reparentShardOpTimings.Reset()
 
 	emergencyReparentOps := EmergencyReparentOptions{}
@@ -2713,11 +2710,6 @@ func TestEmergencyReparenterStats(t *testing.T) {
 	require.EqualValues(t, map[string]int64{"testkeyspace.-.success": 1}, ersCounter.Counts())
 	require.EqualValues(t, map[string]int64{"All": 1, "EmergencyReparentShard": 1}, reparentShardOpTimings.Counts())
 
-	// check the legacy counter values
-	require.EqualValues(t, 1, legacyERSCounter.Get())
-	require.EqualValues(t, 1, legacyERSSuccessCounter.Get())
-	require.EqualValues(t, 0, legacyERSFailureCounter.Get())
-
 	// set emergencyReparentOps to request a non existent tablet
 	emergencyReparentOps.NewPrimaryAlias = &topodatapb.TabletAlias{
 		Cell: "bogus",
@@ -2731,11 +2723,6 @@ func TestEmergencyReparenterStats(t *testing.T) {
 	// check the counter values
 	require.EqualValues(t, map[string]int64{"testkeyspace.-.success": 1, "testkeyspace.-.failure": 1}, ersCounter.Counts())
 	require.EqualValues(t, map[string]int64{"All": 2, "EmergencyReparentShard": 2}, reparentShardOpTimings.Counts())
-
-	// check the legacy counter values
-	require.EqualValues(t, 2, legacyERSCounter.Get())
-	require.EqualValues(t, 1, legacyERSSuccessCounter.Get())
-	require.EqualValues(t, 1, legacyERSFailureCounter.Get())
 }
 
 func TestEmergencyReparenter_findMostAdvanced(t *testing.T) {