Add mempool metrics for number of pending tx and expired txs (#189)

* Add metrics for mempool pending transaction size

* Add expired tx count metrics

internal/mempool/mempool.go

@@ -182,6 +182,11 @@ func (txmp *TxMempool) Size() int {
 	return txSize + pendingSize
 }
 
+// PendingSize returns the number of pending transactions in the mempool.
+func (txmp *TxMempool) PendingSize() int {
+	return txmp.pendingTxs.Size()
+}
+
 // SizeBytes return the total sum in bytes of all the valid transactions in the
 // mempool. It is thread-safe.
 func (txmp *TxMempool) SizeBytes() int64 {
@@ -292,6 +297,7 @@ func (txmp *TxMempool) CheckTx(
 		timestamp: time.Now().UTC(),
 		height:    txmp.height,
 		expiredCallback: func(removeFromCache bool) {
+			txmp.metrics.ExpiredTxs.Add(1)
 			if removeFromCache {
 				txmp.cache.Remove(tx)
 			}
@@ -519,6 +525,7 @@ func (txmp *TxMempool) Update(
 	}
 
 	txmp.metrics.Size.Set(float64(txmp.Size()))
+	txmp.metrics.PendingSize.Set(float64(txmp.PendingSize()))
 	return nil
 }
 
@@ -638,6 +645,7 @@ func (txmp *TxMempool) addNewTransaction(wtx *WrappedTx, res *abci.ResponseCheck
 
 	txmp.metrics.TxSizeBytes.Observe(float64(wtx.Size()))
 	txmp.metrics.Size.Set(float64(txmp.Size()))
+	txmp.metrics.PendingSize.Set(float64(txmp.PendingSize()))
 
 	txmp.insertTx(wtx)
 	txmp.logger.Debug(
@@ -745,6 +753,7 @@ func (txmp *TxMempool) handleRecheckResult(tx types.Tx, res *abci.ResponseCheckT
 	}
 
 	txmp.metrics.Size.Set(float64(txmp.Size()))
+	txmp.metrics.PendingSize.Set(float64(txmp.PendingSize()))
 }
 
 // updateReCheckTxs updates the recheck cursors using the gossipIndex. For

internal/mempool/mempool_test.go

@@ -214,6 +214,7 @@ func TestTxMempool_Size(t *testing.T) {
 	txmp := setup(t, client, 0)
 	txs := checkTxs(ctx, t, txmp, 100, 0)
 	require.Equal(t, len(txs), txmp.Size())
+	require.Equal(t, 0, txmp.PendingSize())
 	require.Equal(t, int64(5690), txmp.SizeBytes())
 
 	rawTxs := make([]types.Tx, len(txs))

internal/mempool/metrics.go

@@ -18,6 +18,9 @@ type Metrics struct {
 	// Number of uncommitted transactions in the mempool.
 	Size metrics.Gauge
 
+	// Number of pending transactions in mempool
+	PendingSize metrics.Gauge
+
 	// Histogram of transaction sizes in bytes.
 	TxSizeBytes metrics.Histogram `metrics_buckettype:"exp" metrics_bucketsizes:"1,3,7"`
 
@@ -38,6 +41,12 @@ type Metrics struct {
 	//metrics:Number of evicted transactions.
 	EvictedTxs metrics.Counter
 
+	// ExpiredTxs defines the number of expired transactions. These are valid
+	// transactions that passed CheckTx and existed in the mempool but were not
+	// get picked up in time and eventually got expired and removed from mempool
+	//metrics:Number of expired transactions.
+	ExpiredTxs metrics.Counter
+
 	// Number of times transactions are rechecked in the mempool.
 	RecheckTimes metrics.Counter
 }