How To “Cancel” Pending Transactions?

Note: Moonriver (MOVR) on Kusama is a companion network to Moonbeam and provides a permanently incentivized canary network. New code ships to Moonriver first, where it can be tested and verified under real economic conditions. Once proven, the same code ships to Moonbeam on Polkadot.

Polygon PoS (polygonscan.com) is an EVM-compatible environment optimized for high throughput and low transaction fees while Polygon zkEVM (zkevm.polygonscan.com) is an EVM-equivalent ZK rollup designed for security.

A transaction on {{chain}} is not as complicated as you might think. There are several things you need to know to make sure that the transaction you are making will go through successfully.

1. Gas Fee

There are many examples of how to explain “Gas Fee.” “Gas Fee”, or commonly called a "Transaction Fee", is a small incentive or fee that is paid to block miners to include your transaction on {{chain}}. The unit of “Gas Fee” is called Gwei and 1 Gwei is equivalent to 0.000000001 {{coin}}.

The way we calculate how much gas fee to pay for a transaction is by multiplying “Gas Price” with “Gas Used.” Do not confuse “Gas Used” with “Gas Limit.” “Gas Used” is the total amount of gas used in the transaction while “Gas Limit” is the maximum number of gas the transaction is allowed to use by the sender.

From one {{chain}} address to another {{chain}} address, the gas needed for sending {{coin}} is exactly 21000 gas. Thus when sending {{coin}} to another address (instead of a contract address), a 21000 gas limit is enough. Using a gas price of 20 Gwei, the total gas fee paid for the particular transaction above is:

21000 gas x 20 Gwei = 420000 Gwei = 0.00042 {{coin}}

The gas used for executing a contract is different from one contract to another. It is recommended to check the previous transactions from the contract address and to expect a little more while setting gas limit during a transaction involving a contract.

2. Network Congestion

Network congestion plays an important role in the amount of gas price users would need to pay and the speed of the transaction. Pending transactions on {{chain}} network determine how congested the network is. The more congested the network is, the higher the gas price users would need to pay to secure their transactions on the blockchain.

Block producers will favor transactions that have a higher gas price thus including transactions that pay a higher gas price first before those with a lower gas price. {{chain}} Gas Price Tracker is a simple tool that helps users determine the safe and recommended gas price to use while performing a transaction at a particular point in time. The gas price tracker also provides an estimate of the time needed for a transaction to be included in the blockchain for a given gas price.

3. Nonce

A nonce is the number of the transaction of the sender’s address. Every transaction from an address is numbered sequentially, beginning with 0 for the first transaction. For example, if the nonce of a transaction is 10, it is the 11th transaction sent from the sender’s address.

The nonce is essential to take note of especially if you perform multiple transactions using the same address. {{chain}} works in a way that a transaction with a lower nonce will be processed first before any other, thus if you have a problem with an earlier transaction, the ensuing transaction will not be included in the blockchain until the one with the lower nonce is successfully included.

Replacing / Cancelling Pending Transactions

Replacing a transaction on the blockchain is a little tricky.

A bit of context to begin with. The block producers prioritize transactions that pay a higher gas fee. When you send a transaction on {{chain}}, it is sent to a “pending transaction pool” and the transaction you have just sent is sitting there waiting for block producers to include it into the blockchain.

Block producers will “pick” transactions that pay a higher gas fee leaving transactions with low gas fees at the bottom of the queue. This is where your transaction might be hanging and in the midst of network congestion (see above), your transaction might take a while to be included since more transactions are being added into the pool offering higher gas fees than your transaction.

Remember Nonce? (see above)

The trick to “cancel” your pending transaction is by replacing the transaction with another 0 {{coin}} transaction with a higher gas fee sending to yourself with the same nonce as the pending transaction.

How to determine the nonce of your pending transaction? Look up your transaction hash (txhash) on {{explorer}} and find your nonce for the pending transaction below.