core/txpool/legacypool: add metric for accounts in txpool (#33646)

This PR adds metrics that count the number of accounts having transactions 
in the txpool. Together with the transaction count this can be used as a 
simple indicator of the diversity of transactions in the pool.

Note: as an alternative implementation, we could use a periodic or event
driven update of these Gauges using len.

I've preferred this implementation to match what we have for the pool
sizes.

---------

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

core/txpool/legacypool/legacypool.go

@@ -114,6 +114,9 @@ var (
 	queuedGauge  = metrics.NewRegisteredGauge("txpool/queued", nil)
 	slotsGauge   = metrics.NewRegisteredGauge("txpool/slots", nil)
 
+	pendingAddrsGauge = metrics.NewRegisteredGauge("txpool/pending/accounts", nil)
+	queuedAddrsGauge  = metrics.NewRegisteredGauge("txpool/queued/accounts", nil)
+
 	reheapTimer = metrics.NewRegisteredTimer("txpool/reheap", nil)
 )
 
@@ -844,6 +847,7 @@ func (pool *LegacyPool) promoteTx(addr common.Address, hash common.Hash, tx *typ
 	// Try to insert the transaction into the pending queue
 	if pool.pending[addr] == nil {
 		pool.pending[addr] = newList(true)
+		pendingAddrsGauge.Inc(1)
 	}
 	list := pool.pending[addr]
 
@@ -1083,6 +1087,7 @@ func (pool *LegacyPool) removeTx(hash common.Hash, outofbound bool, unreserve bo
 			// If no more pending transactions are left, remove the list
 			if pending.Empty() {
 				delete(pool.pending, addr)
+				pendingAddrsGauge.Dec(1)
 			}
 			// Postpone any invalidated transactions
 			for _, tx := range invalids {
@@ -1580,6 +1585,7 @@ func (pool *LegacyPool) demoteUnexecutables() {
 		// Delete the entire pending entry if it became empty.
 		if list.Empty() {
 			delete(pool.pending, addr)
+			pendingAddrsGauge.Dec(1)
 			if _, ok := pool.queue.get(addr); !ok {
 				pool.reserver.Release(addr)
 			}
@@ -1839,6 +1845,9 @@ func (pool *LegacyPool) Clear() {
 	pool.pending = make(map[common.Address]*list)
 	pool.queue = newQueue(pool.config, pool.signer)
 	pool.pendingNonces = newNoncer(pool.currentState)
+
+	pendingAddrsGauge.Update(0)
+	queuedAddrsGauge.Update(0)
 }
 
 // HasPendingAuth returns a flag indicating whether there are pending

core/txpool/legacypool/queue.go

@@ -114,6 +114,7 @@ func (q *queue) remove(addr common.Address, tx *types.Transaction) {
 		if future.Empty() {
 			delete(q.queued, addr)
 			delete(q.beats, addr)
+			queuedAddrsGauge.Dec(1)
 		}
 	}
 }
@@ -123,6 +124,7 @@ func (q *queue) add(tx *types.Transaction) (*common.Hash, error) {
 	from, _ := types.Sender(q.signer, tx) // already validated
 	if q.queued[from] == nil {
 		q.queued[from] = newList(false)
+		queuedAddrsGauge.Inc(1)
 	}
 	inserted, old := q.queued[from].Add(tx, q.config.PriceBump)
 	if !inserted {
@@ -200,6 +202,7 @@ func (q *queue) promoteExecutables(accounts []common.Address, gasLimit uint64, c
 		if list.Empty() {
 			delete(q.queued, addr)
 			delete(q.beats, addr)
+			queuedAddrsGauge.Dec(1)
 			removedAddresses = append(removedAddresses, addr)
 		}
 	}