Propagate transactions for next 4 blocks. (#9265)

Closes #9255 

This PR also removes the limit of max 64 transactions per packet, currently we only attempt to prevent the packet size to go over 8MB. This will only be the case for super-large transactions or high-block-gas-limit chains.

Patching this is important only for chains that have blocks that can fit more than 4k transactions (over 86M block gas limit)

For mainnet, we should actually see a tiny bit faster propagation since instead of computing 4k pending set, we only need `4 * 8M / 21k = 1523` transactions.

Running some tests on `dekompile` node right now, to check how it performs in the wild.

ethcore/src/client/client.rs

@@ -15,6 +15,7 @@
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
 use std::collections::{HashSet, BTreeMap, VecDeque};
+use std::cmp;
 use std::fmt;
 use std::str::FromStr;
 use std::sync::atomic::{AtomicUsize, AtomicBool, Ordering as AtomicOrdering};
@@ -1945,7 +1946,25 @@ impl BlockChainClient for Client {
 		(*self.build_last_hashes(&self.chain.read().best_block_hash())).clone()
 	}
 
-	fn ready_transactions(&self, max_len: usize) -> Vec<Arc<VerifiedTransaction>> {
+	fn transactions_to_propagate(&self) -> Vec<Arc<VerifiedTransaction>> {
+		const PROPAGATE_FOR_BLOCKS: u32 = 4;
+		const MIN_TX_TO_PROPAGATE: usize = 256;
+
+		let block_gas_limit = *self.best_block_header().gas_limit();
+		let min_tx_gas: U256 = self.latest_schedule().tx_gas.into();
+
+		let max_len = if min_tx_gas.is_zero() {
+			usize::max_value()
+		} else {
+			cmp::max(
+				MIN_TX_TO_PROPAGATE,
+				cmp::min(
+					(block_gas_limit / min_tx_gas) * PROPAGATE_FOR_BLOCKS,
+					// never more than usize
+					usize::max_value().into()
+				).as_u64() as usize
+			)
+		};
 		self.importer.miner.ready_transactions(self, max_len, ::miner::PendingOrdering::Priority)
 	}
 

ethcore/src/client/test_client.rs

@@ -807,8 +807,8 @@ impl BlockChainClient for TestBlockChainClient {
 		self.traces.read().clone()
 	}
 
-	fn ready_transactions(&self, max_len: usize) -> Vec<Arc<VerifiedTransaction>> {
-		self.miner.ready_transactions(self, max_len, miner::PendingOrdering::Priority)
+	fn transactions_to_propagate(&self) -> Vec<Arc<VerifiedTransaction>> {
+		self.miner.ready_transactions(self, 4096, miner::PendingOrdering::Priority)
 	}
 
 	fn signing_chain_id(&self) -> Option<u64> { None }

ethcore/src/client/traits.rs

@@ -321,8 +321,8 @@ pub trait BlockChainClient : Sync + Send + AccountData + BlockChain + CallContra
 	/// Get last hashes starting from best block.
 	fn last_hashes(&self) -> LastHashes;
 
-	/// List all transactions that are allowed into the next block.
-	fn ready_transactions(&self, max_len: usize) -> Vec<Arc<VerifiedTransaction>>;
+	/// List all ready transactions that should be propagated to other peers.
+	fn transactions_to_propagate(&self) -> Vec<Arc<VerifiedTransaction>>;
 
 	/// Sorted list of transaction gas prices from at least last sample_size blocks.
 	fn gas_price_corpus(&self, sample_size: usize) -> ::stats::Corpus<U256> {