do not build empty blocks on detecting an overflow (#1525)

also stop processing transactions when the block timer has ticked to
give more consistent block times

zk/debug_tools/test-contracts/contracts/GasBurner.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.15;
+
+contract GasBurner {
+    constructor() {
+      //dynamic array
+      uint[] memory a = new uint[](12000);
+        for (uint i = 0; i < 2000; i++) {
+            a[i%10000] = i;
+        }
+    }
+}

zk/debug_tools/test-contracts/package.json

@@ -21,7 +21,8 @@
     "chainCall:local": "npx hardhat compile && npx hardhat run scripts/chain-call.js --network local",
     "chainCall:sepolia": "npx hardhat compile && npx hardhat run scripts/chain-call.js --network sepolia",
     "create:local": "npx hardhat compile && npx hardhat run scripts/create.js --network local",
-    "keccak:local": "npx hardhat compile && npx hardhat run scripts/keccak-loop.js --network local"
+    "keccak:local": "npx hardhat compile && npx hardhat run scripts/keccak-loop.js --network local",
+    "gasBurner:local": "npx hardhat compile && npx hardhat run scripts/gas-burner.js --network local"
   },
   "keywords": [],
   "author": "",

zk/debug_tools/test-contracts/scripts/gas-burner.js

@@ -0,0 +1,26 @@
+async function main() {
+try {
+   // Get the ContractFactory of your BigLoopContract
+   const GasBurnerContract = await hre.ethers.getContractFactory("GasBurner");
+
+   // Deploy the contract
+   const contract = await GasBurnerContract.deploy();
+   // Wait for the deployment transaction to be mined
+   await contract.waitForDeployment();
+
+   console.log(`GasBurner deployed to: ${await contract.getAddress()}`);
+
+  //  const result = await contract.bigLoop(10000);
+  //  console.log(result);
+ } catch (error) {
+   console.error(error);
+   process.exit(1);
+ }
+}
+
+main()
+  .then(() => process.exit(0))
+  .catch(error => {
+    console.error(error);
+    process.exit(1);
+  });

zk/stages/stage_sequence_execute.go

@@ -307,16 +307,22 @@ func sequencingBatchStep(
 			log.Info(fmt.Sprintf("[%s] Waiting for txs from the pool...", logPrefix))
 		}
 
-	LOOP_TRANSACTIONS:
+		innerBreak := false
+		emptyBlockOverflow := false
+
+	OuterLoopTransactions:
 		for {
+			if innerBreak {
+				break
+			}
 			select {
 			case <-logTicker.C:
 				if !batchState.isAnyRecovery() {
 					log.Info(fmt.Sprintf("[%s] Waiting some more for txs from the pool...", logPrefix))
 				}
 			case <-blockTicker.C:
 				if !batchState.isAnyRecovery() {
-					break LOOP_TRANSACTIONS
+					break OuterLoopTransactions
 				}
 			case <-batchTicker.C:
 				if !batchState.isAnyRecovery() {
@@ -380,7 +386,19 @@ func sequencingBatchStep(
 
 				badTxHashes := make([]common.Hash, 0)
 				minedTxHashes := make([]common.Hash, 0)
+
+			InnerLoopTransactions:
 				for i, transaction := range batchState.blockState.transactionsForInclusion {
+					// quick check if we should stop handling transactions
+					select {
+					case <-blockTicker.C:
+						if !batchState.isAnyRecovery() {
+							innerBreak = true
+							break InnerLoopTransactions
+						}
+					default:
+					}
+
 					txHash := transaction.Hash()
 					effectiveGas := batchState.blockState.getL1EffectiveGases(cfg, i)
 
@@ -457,7 +475,10 @@ func sequencingBatchStep(
 								if batchState.reachedOverflowTransactionLimit() || cfg.zk.SealBatchImmediatelyOnOverflow {
 									log.Info(fmt.Sprintf("[%s] closing batch due to counters", logPrefix), "counters: ", batchState.overflowTransactions, "immediate", cfg.zk.SealBatchImmediatelyOnOverflow)
 									runLoopBlocks = false
-									break LOOP_TRANSACTIONS
+									if len(batchState.blockState.builtBlockElements.transactions) == 0 {
+										emptyBlockOverflow = true
+									}
+									break OuterLoopTransactions
 								}
 							}
 
@@ -474,7 +495,7 @@ func sequencingBatchStep(
 						}
 						log.Info(fmt.Sprintf("[%s] gas overflowed adding transaction to block", logPrefix), "block", blockNumber, "tx-hash", txHash)
 						runLoopBlocks = false
-						break LOOP_TRANSACTIONS
+						break OuterLoopTransactions
 					case overflowNone:
 					}
 
@@ -494,12 +515,12 @@ func sequencingBatchStep(
 					if len(batchState.blockState.transactionsForInclusion) == 0 {
 						// We need to jump to the next block here if there are no transactions in current block
 						batchState.resequenceBatchJob.UpdateLastProcessedTx(batchState.resequenceBatchJob.CurrentBlock().L2Blockhash)
-						break LOOP_TRANSACTIONS
+						break OuterLoopTransactions
 					}
 
 					if batchState.resequenceBatchJob.AtNewBlockBoundary() {
 						// We need to jump to the next block here if we are at the end of the current block
-						break LOOP_TRANSACTIONS
+						break OuterLoopTransactions
 					} else {
 						if cfg.zk.SequencerResequenceStrict {
 							return fmt.Errorf("strict mode enabled, but resequenced batch %d has transactions that overflowed counters or failed transactions", batchState.batchNumber)
@@ -533,16 +554,23 @@ func sequencingBatchStep(
 						log.Info(fmt.Sprintf("[%s] L1 recovery no more transactions to recover", logPrefix))
 					}
 
-					break LOOP_TRANSACTIONS
+					break OuterLoopTransactions
 				}
 
 				if batchState.isLimboRecovery() {
 					runLoopBlocks = false
-					break LOOP_TRANSACTIONS
+					break OuterLoopTransactions
 				}
 			}
 		}
 
+		// we do not want to commit this block if it has no transactions and we detected an overflow - essentially the batch is too
+		// full to get any more transactions in it and we don't want to commit an empty block
+		if emptyBlockOverflow {
+			log.Info(fmt.Sprintf("[%s] Block %d overflow detected with no transactions added, skipping block for next batch", logPrefix, blockNumber))
+			break
+		}
+
 		if block, err = doFinishBlockAndUpdateState(batchContext, ibs, header, parentBlock, batchState, ger, l1BlockHash, l1TreeUpdateIndex, infoTreeIndexProgress, batchCounters); err != nil {
 			return err
 		}