chore: add pending imports metrics (#3344)

crates/net/network/src/metrics.rs

@@ -54,6 +54,8 @@ pub struct TransactionsManagerMetrics {
     pub(crate) messages_with_already_seen_hashes: Counter,
     /// Total number of messages with already seen full transactions
     pub(crate) messages_with_already_seen_transactions: Counter,
+    /// Number of transactions about to be imported into the pool.
+    pub(crate) pending_pool_imports: Gauge,
 }
 
 /// Metrics for Disconnection types

crates/net/network/src/transactions.rs

@@ -158,6 +158,10 @@ where
         TransactionsHandle { manager_tx: self.command_tx.clone() }
     }
 
+    fn update_import_metrics(&self) {
+        self.metrics.pending_pool_imports.set(self.pool_imports.len() as f64);
+    }
+
     /// Request handler for an incoming request for transactions
     fn on_get_pooled_transactions(
         &mut self,
@@ -538,6 +542,8 @@ where
             }
         }
 
+        this.update_import_metrics();
+
         // Advance all imports
         while let Poll::Ready(Some(import_res)) = this.pool_imports.poll_next_unpin(cx) {
             match import_res {
@@ -558,6 +564,8 @@ where
             }
         }
 
+        this.update_import_metrics();
+
         // handle and propagate new transactions
         let mut new_txs = Vec::new();
         while let Poll::Ready(Some(hash)) = this.pending_transactions.poll_next_unpin(cx) {