Fix quadratic iterations over transaction pool (#4736)

* transaction pool changes

* service & network changes

* address review

* reduce future pool

substrate/client/service/src/builder.rs

@@ -906,9 +906,9 @@ ServiceBuilder<
 			let network = Arc::downgrade(&network);
 			let transaction_pool_ = transaction_pool.clone();
 			let events = transaction_pool.import_notification_stream()
-				.for_each(move |_| {
+				.for_each(move |hash| {
 					if let Some(network) = network.upgrade() {
-						network.trigger_repropagate();
+						network.propagate_extrinsic(hash);
 					}
 					let status = transaction_pool_.status();
 					telemetry!(SUBSTRATE_INFO; "txpool.import";

substrate/client/service/src/lib.rs

@@ -608,7 +608,7 @@ where
 	H: std::hash::Hash + Eq + sp_runtime::traits::Member + sp_runtime::traits::MaybeSerialize,
 	E: 'static + IntoPoolError + From<sp_transaction_pool::error::Error>,
 {
-	fn transactions(&self) -> Vec<(H, <B as BlockT>::Extrinsic)> {
+	fn transactions(&self) -> Vec<(H, B::Extrinsic)> {
 		transactions_to_propagate(&*self.pool)
 	}
 
@@ -660,6 +660,10 @@ where
 	fn on_broadcasted(&self, propagations: HashMap<H, Vec<String>>) {
 		self.pool.on_broadcasted(propagations)
 	}
+
+	fn transaction(&self, hash: &H) -> Option<B::Extrinsic> {
+		self.pool.ready_transaction(hash).map(|tx| tx.data().clone())
+	}
 }
 
 #[cfg(test)]