Configurable max block weight for mining (aka soft limit) (#1976)

config/src/comments.rs

@@ -247,6 +247,13 @@ fn comments() -> HashMap<String, String> {
 ".to_string(),
 	);
 
+	retval.insert(
+		"mineable_max_weight".to_string(),
+		"
+#maximum total weight of transactions that can get selected to build a block
+".to_string(),
+	);
+
 	retval.insert(
 		"[server.stratum_mining_config]".to_string(),
 		"

pool/src/pool.rs

@@ -19,7 +19,6 @@ use std::collections::{HashMap, HashSet};
 use std::sync::Arc;
 use util::RwLock;
 
-use core::consensus;
 use core::core::hash::{Hash, Hashed};
 use core::core::id::{ShortId, ShortIdentifiable};
 use core::core::transaction;
@@ -27,10 +26,6 @@ use core::core::verifier_cache::VerifierCache;
 use core::core::{Block, BlockHeader, BlockSums, Committed, Transaction, TxKernel};
 use types::{BlockChain, PoolEntry, PoolEntryState, PoolError};
 
-// max weight leaving minimum space for a coinbase
-const MAX_MINEABLE_WEIGHT: usize =
-	consensus::MAX_BLOCK_WEIGHT - consensus::BLOCK_OUTPUT_WEIGHT - consensus::BLOCK_KERNEL_WEIGHT;
-
 pub struct Pool {
 	/// Entries in the pool (tx + info + timer) in simple insertion order.
 	pub entries: Vec<PoolEntry>,
@@ -120,7 +115,7 @@ impl Pool {
 	/// appropriate to put in a mined block. Aggregates chains of dependent
 	/// transactions, orders by fee over weight and ensures to total weight
 	/// doesn't exceed block limits.
-	pub fn prepare_mineable_transactions(&self) -> Result<Vec<Transaction>, PoolError> {
+	pub fn prepare_mineable_transactions(&self, max_weight: usize) -> Result<Vec<Transaction>, PoolError> {
 		let header = self.blockchain.chain_head()?;
 		let tx_buckets = self.bucket_transactions();
 
@@ -139,7 +134,7 @@ impl Pool {
 		let mut weight = 0;
 		flat_txs.retain(|tx| {
 			weight += tx.tx_weight_as_block() as usize;
-			weight < MAX_MINEABLE_WEIGHT
+			weight < max_weight
 		});
 
 		// Iteratively apply the txs to the current chain state,

pool/src/transaction_pool.rs

@@ -255,6 +255,6 @@ impl TransactionPool {
 	/// Returns a vector of transactions from the txpool so we can build a
 	/// block from them.
 	pub fn prepare_mineable_transactions(&self) -> Result<Vec<Transaction>, PoolError> {
-		self.txpool.prepare_mineable_transactions()
+		self.txpool.prepare_mineable_transactions(self.config.mineable_max_weight)
 	}
 }

pool/src/types.rs

@@ -100,6 +100,12 @@ pub struct PoolConfig {
 	/// Maximum capacity of the pool in number of transactions
 	#[serde = "default_max_stempool_size"]
 	pub max_stempool_size: usize,
+
+	/// Maximum total weight of transactions that can get selected to build a
+	/// block from. Allows miners to restrict the maximum weight of their
+	/// blocks.
+	#[serde = "default_mineable_max_weight"]
+	pub mineable_max_weight: usize,
 }
 
 impl Default for PoolConfig {
@@ -108,6 +114,7 @@ impl Default for PoolConfig {
 			accept_fee_base: default_accept_fee_base(),
 			max_pool_size: default_max_pool_size(),
 			max_stempool_size: default_max_stempool_size(),
+			mineable_max_weight: default_mineable_max_weight(),
 		}
 	}
 }
@@ -121,6 +128,9 @@ fn default_max_pool_size() -> usize {
 fn default_max_stempool_size() -> usize {
 	50_000
 }
+fn default_mineable_max_weight() -> usize {
+	consensus::MAX_BLOCK_WEIGHT - consensus::BLOCK_OUTPUT_WEIGHT - consensus::BLOCK_KERNEL_WEIGHT
+}
 
 /// Represents a single entry in the pool.
 /// A single (possibly aggregated) transaction.

pool/tests/common/mod.rs

@@ -169,6 +169,7 @@ pub fn test_setup(
 			accept_fee_base: 0,
 			max_pool_size: 50,
 			max_stempool_size: 50,
+			mineable_max_weight: 10_000,
 		},
 		chain.clone(),
 		verifier_cache.clone(),