fix: panic in prometheus (#1427)

We witnessed this panic in one of our testnets using the v2 mempool
caused from incorrectly configuring prometheus.

```
panic: inconsistent label cardinality: expected 3 label values but got 2 in prometheus.Labels{"chain_id":"test", "version":"6f334a2"}

goroutine 151 [running]:
github.com/prometheus/client_golang/prometheus.(*CounterVec).With(...)
	/go/pkg/mod/github.com/prometheus/[email protected]/prometheus/counter.go:296
github.com/go-kit/kit/metrics/prometheus.(*Counter).Add(0xc0013035a0, 0x0)
	/go/pkg/mod/github.com/go-kit/[email protected]/metrics/prometheus/prometheus.go:45 +0x131
github.com/tendermint/tendermint/mempool/cat.(*TxPool).CheckToPurgeExpiredTxs(0xc0012f7d40)
```

This PR fixes this problem. To make things safer in the future, it
introduces a new metric "ExpiredTxs", specifically for those
transactions that were kicked from the mempool due to the TTL

mempool/cat/pool.go

@@ -747,7 +747,7 @@ func (txmp *TxPool) purgeExpiredTxs(blockHeight int64) {
 	for _, tx := range purgedTxs {
 		txmp.evictedTxCache.Push(tx.key)
 	}
-	txmp.metrics.EvictedTxs.Add(float64(numExpired))
+	txmp.metrics.ExpiredTxs.Add(float64(numExpired))
 
 	// purge old evicted and seen transactions
 	if txmp.config.TTLDuration == 0 {

mempool/metrics.go

@@ -11,17 +11,6 @@ const (
 	// MetricsSubsystem is a subsystem shared by all metrics exposed by this
 	// package.
 	MetricsSubsystem = "mempool"
-
-	TypeLabel = "type"
-
-	FailedPrecheck = "precheck"
-	FailedAdding   = "adding"
-	FailedRecheck  = "recheck"
-
-	EvictedNewTxFullMempool      = "full-removed-incoming"
-	EvictedExistingTxFullMempool = "full-removed-existing"
-	EvictedTxExpiredBlocks       = "expired-ttl-blocks"
-	EvictedTxExpiredTime         = "expired-ttl-time"
 )
 
 // Metrics contains metrics exposed by this package.
@@ -42,10 +31,13 @@ type Metrics struct {
 
 	// EvictedTxs defines the number of evicted transactions. These are valid
 	// transactions that passed CheckTx and existed in the mempool but were later
-	// evicted to make room for higher priority valid transactions that passed
-	// CheckTx.
+	// evicted to make room for higher priority valid transactions
 	EvictedTxs metrics.Counter
 
+	// ExpiredTxs defines transactions that were removed from the mempool due
+	// to a TTL
+	ExpiredTxs metrics.Counter
+
 	// SuccessfulTxs defines the number of transactions that successfully made
 	// it into a block.
 	SuccessfulTxs metrics.Counter
@@ -75,7 +67,6 @@ func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
 	for i := 0; i < len(labelsAndValues); i += 2 {
 		labels = append(labels, labelsAndValues[i])
 	}
-	typedCounterLabels := append(append(make([]string, 0, len(labels)+1), labels...), TypeLabel)
 	return &Metrics{
 		Size: prometheus.NewGaugeFrom(stdprometheus.GaugeOpts{
 			Namespace: namespace,
@@ -104,14 +95,21 @@ func PrometheusMetrics(namespace string, labelsAndValues ...string) *Metrics {
 			Subsystem: MetricsSubsystem,
 			Name:      "failed_txs",
 			Help:      "Number of failed transactions.",
-		}, typedCounterLabels).With(labelsAndValues...),
+		}, labels).With(labelsAndValues...),
 
 		EvictedTxs: prometheus.NewCounterFrom(stdprometheus.CounterOpts{
 			Namespace: namespace,
 			Subsystem: MetricsSubsystem,
 			Name:      "evicted_txs",
 			Help:      "Number of evicted transactions.",
-		}, typedCounterLabels).With(labelsAndValues...),
+		}, labels).With(labelsAndValues...),
+
+		ExpiredTxs: prometheus.NewCounterFrom(stdprometheus.CounterOpts{
+			Namespace: namespace,
+			Subsystem: MetricsSubsystem,
+			Name:      "expired_txs",
+			Help:      "Number of expired transactions.",
+		}, labels).With(labelsAndValues...),
 
 		SuccessfulTxs: prometheus.NewCounterFrom(stdprometheus.CounterOpts{
 			Namespace: namespace,
@@ -158,6 +156,7 @@ func NopMetrics() *Metrics {
 		TxSizeBytes:    discard.NewHistogram(),
 		FailedTxs:      discard.NewCounter(),
 		EvictedTxs:     discard.NewCounter(),
+		ExpiredTxs:     discard.NewCounter(),
 		SuccessfulTxs:  discard.NewCounter(),
 		RecheckTimes:   discard.NewCounter(),
 		AlreadySeenTxs: discard.NewCounter(),

mempool/v1/mempool.go

@@ -204,7 +204,7 @@ func (txmp *TxMempool) CheckTx(tx types.Tx, cb func(*abci.Response), txInfo memp
 		// If a precheck hook is defined, call it before invoking the application.
 		if txmp.preCheck != nil {
 			if err := txmp.preCheck(tx); err != nil {
-				txmp.metrics.FailedTxs.With(mempool.TypeLabel, mempool.FailedPrecheck).Add(1)
+				txmp.metrics.FailedTxs.Add(1)
 				return 0, mempool.ErrPreCheck{Reason: err}
 			}
 		}
@@ -500,7 +500,7 @@ func (txmp *TxMempool) addNewTransaction(wtx *WrappedTx, checkTxRes *abci.Respon
 			"post_check_err", err,
 		)
 
-		txmp.metrics.FailedTxs.With(mempool.TypeLabel, mempool.FailedAdding).Add(1)
+		txmp.metrics.FailedTxs.Add(1)
 
 		// Remove the invalid transaction from the cache, unless the operator has
 		// instructed us to keep invalid transactions.
@@ -568,7 +568,7 @@ func (txmp *TxMempool) addNewTransaction(wtx *WrappedTx, checkTxRes *abci.Respon
 			checkTxRes.MempoolError =
 				fmt.Sprintf("rejected valid incoming transaction; mempool is full (%X)",
 					wtx.tx.Hash())
-			txmp.metrics.EvictedTxs.With(mempool.TypeLabel, mempool.EvictedNewTxFullMempool).Add(1)
+			txmp.metrics.EvictedTxs.Add(1)
 			// Add it to evicted transactions cache
 			txmp.evictedTxs.Push(wtx.tx)
 			return
@@ -602,7 +602,7 @@ func (txmp *TxMempool) addNewTransaction(wtx *WrappedTx, checkTxRes *abci.Respon
 			)
 			txmp.removeTxByElement(vic)
 			txmp.cache.Remove(w.tx)
-			txmp.metrics.EvictedTxs.With(mempool.TypeLabel, mempool.EvictedExistingTxFullMempool).Add(1)
+			txmp.metrics.EvictedTxs.Add(1)
 			// Add it to evicted transactions cache
 			txmp.evictedTxs.Push(w.tx)
 			// We may not need to evict all the eligible transactions.  Bail out
@@ -681,7 +681,7 @@ func (txmp *TxMempool) handleRecheckResult(tx types.Tx, checkTxRes *abci.Respons
 		"code", checkTxRes.Code,
 	)
 	txmp.removeTxByElement(elt)
-	txmp.metrics.FailedTxs.With(mempool.TypeLabel, mempool.FailedRecheck).Add(1)
+	txmp.metrics.FailedTxs.Add(1)
 	if !txmp.config.KeepInvalidTxsInCache {
 		txmp.cache.Remove(wtx.tx)
 	}
@@ -791,16 +791,12 @@ func (txmp *TxMempool) purgeExpiredTxs(blockHeight int64) {
 		next := cur.Next()
 
 		w := cur.Value.(*WrappedTx)
-		if txmp.config.TTLNumBlocks > 0 && (blockHeight-w.height) > txmp.config.TTLNumBlocks {
+		if txmp.config.TTLNumBlocks > 0 && (blockHeight-w.height) > txmp.config.TTLNumBlocks ||
+			txmp.config.TTLDuration > 0 && now.Sub(w.timestamp) > txmp.config.TTLDuration {
 			txmp.removeTxByElement(cur)
 			txmp.cache.Remove(w.tx)
-			txmp.metrics.EvictedTxs.With(mempool.TypeLabel, mempool.EvictedTxExpiredBlocks).Add(1)
 			txmp.evictedTxs.Push(w.tx)
-		} else if txmp.config.TTLDuration > 0 && now.Sub(w.timestamp) > txmp.config.TTLDuration {
-			txmp.removeTxByElement(cur)
-			txmp.cache.Remove(w.tx)
-			txmp.evictedTxs.Push(w.tx)
-			txmp.metrics.EvictedTxs.With(mempool.TypeLabel, mempool.EvictedTxExpiredTime).Add(1)
+			txmp.metrics.ExpiredTxs.Add(1)
 		}
 		cur = next
 	}