core/txpool/blobpool: fix gapped queue size cap (#34831)

the gapped queue cap was effectively per-sender rather than total — a
sender pool spread across enough distinct addresses could grow
`p.gapped` well past `maxGapped`, defeating the resource bound.

`maxGapped` was being compared against `len(p.gapped)`, which is a
`map[address][]tx` and counts unique senders, not queued txs. Switched
the check to `len(p.gappedSource)` (keyed by tx hash, so its length is
the real total). Also wired up a `blobpool/gapped/count` gauge plus
`promoted`, `evicted`, and `gappedfull` meters so queue size and churn
are actually observable in prod.

core/txpool/blobpool/blobpool.go

@@ -1596,9 +1596,10 @@ func (p *BlobPool) addLocked(tx *types.Transaction, checkGapped bool) (err error
 			// Store the tx in memory, and revalidate later
 			from, _ := types.Sender(p.signer, tx)
 			allowance := p.gappedAllowance(from)
-			if allowance >= 1 && len(p.gapped) < maxGapped {
+			if allowance >= 1 && len(p.gappedSource) < maxGapped {
 				p.gapped[from] = append(p.gapped[from], tx)
 				p.gappedSource[tx.Hash()] = from
+				gappedGauge.Update(int64(len(p.gappedSource)))
 				log.Trace("added tx to gapped blob queue", "allowance", allowance, "hash", tx.Hash(), "from", from, "nonce", tx.Nonce(), "qlen", len(p.gapped[from]))
 				return nil
 			} else {
@@ -1606,6 +1607,7 @@ func (p *BlobPool) addLocked(tx *types.Transaction, checkGapped bool) (err error
 				// transactions by keeping the old and dropping this one.
 				// Thus replacing a gapped transaction with another gapped transaction
 				// is discouraged.
+				addGappedFullMeter.Mark(1)
 				log.Trace("no gapped blob queue allowance", "allowance", allowance, "hash", tx.Hash(), "from", from, "nonce", tx.Nonce(), "qlen", len(p.gapped[from]))
 			}
 		case errors.Is(err, core.ErrInsufficientFunds):
@@ -1791,6 +1793,7 @@ func (p *BlobPool) addLocked(tx *types.Transaction, checkGapped bool) (err error
 				// We do not recurse here, but continue to loop instead.
 				// We are under lock, so we can add the transaction directly.
 				if err := p.addLocked(tx, false); err == nil {
+					gappedPromotedMeter.Mark(1)
 					log.Trace("Gapped blob transaction added to pool", "hash", tx.Hash(), "from", from, "nonce", tx.Nonce(), "qlen", len(p.gapped[from]))
 				} else {
 					log.Trace("Gapped blob transaction not accepted", "hash", tx.Hash(), "from", from, "nonce", tx.Nonce(), "err", err)
@@ -1802,6 +1805,7 @@ func (p *BlobPool) addLocked(tx *types.Transaction, checkGapped bool) (err error
 		} else {
 			p.gapped[from] = gtxs
 		}
+		gappedGauge.Update(int64(len(p.gappedSource)))
 	}
 	return nil
 }
@@ -2069,8 +2073,9 @@ func (p *BlobPool) evictGapped() {
 				keep = append(keep, gtx)
 			}
 		}
-		if len(keep) < len(txs) {
-			log.Trace("Evicting old gapped blob transactions", "count", len(txs)-len(keep), "from", from)
+		if evicted := len(txs) - len(keep); evicted > 0 {
+			gappedEvictedMeter.Mark(int64(evicted))
+			log.Trace("Evicting old gapped blob transactions", "count", evicted, "from", from)
 		}
 		if len(keep) == 0 {
 			delete(p.gapped, from)
@@ -2078,6 +2083,7 @@ func (p *BlobPool) evictGapped() {
 			p.gapped[from] = keep
 		}
 	}
+	gappedGauge.Update(int64(len(p.gappedSource)))
 }
 
 // isAnnouncable checks whether a transaction is announcable based on its

core/txpool/blobpool/metrics.go

@@ -97,9 +97,15 @@ var (
 	addUnderpricedMeter  = metrics.NewRegisteredMeter("blobpool/add/underpriced", nil)  // Gas tip too low, neutral
 	addStaleMeter        = metrics.NewRegisteredMeter("blobpool/add/stale", nil)        // Nonce already filled, reject, bad-ish
 	addGappedMeter       = metrics.NewRegisteredMeter("blobpool/add/gapped", nil)       // Nonce gapped, reject, bad-ish
+	addGappedFullMeter   = metrics.NewRegisteredMeter("blobpool/add/gappedfull", nil)   // Gapped queue full, reject, neutral
 	addOverdraftedMeter  = metrics.NewRegisteredMeter("blobpool/add/overdrafted", nil)  // Balance exceeded, reject, neutral
 	addOvercappedMeter   = metrics.NewRegisteredMeter("blobpool/add/overcapped", nil)   // Per-account cap exceeded, reject, neutral
 	addNoreplaceMeter    = metrics.NewRegisteredMeter("blobpool/add/noreplace", nil)    // Replacement fees or tips too low, neutral
 	addNonExclusiveMeter = metrics.NewRegisteredMeter("blobpool/add/nonexclusive", nil) // Plain transaction from same account exists, reject, neutral
 	addValidMeter        = metrics.NewRegisteredMeter("blobpool/add/valid", nil)        // Valid transaction, add, neutral
+
+	// Gapped queue metrics for observability
+	gappedGauge         = metrics.NewRegisteredGauge("blobpool/gapped/count", nil)    // Current gapped queue size
+	gappedPromotedMeter = metrics.NewRegisteredMeter("blobpool/gapped/promoted", nil) // Gapped txs successfully promoted to pool
+	gappedEvictedMeter  = metrics.NewRegisteredMeter("blobpool/gapped/evicted", nil)  // Gapped txs evicted due to timeout/stale
 )