Category Archives: mempool

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Biggest Bitcoin Mempool Since January 2018 Cleared in Only 2 Days

On 15 November, the Bitcoin mempool saw its biggest flood since January 2018, with the mempool size hitting 94 MB at one point. However, it only took two days for the mempool to completely clear out in this case. This situation is a testament to the efficiency of the Bitcoin network.

The mempool is all of the transactions that are unconfirmed, meaning they have not been included in a block yet. The mempool periodically spikes to 5-15 MB, but this week 90,000 transactions totaling 94 MB flooded in all at once. Apparently this mempool flood was caused by a Bitcoin user consolidating all of their dust transactions.

Essentially, over time a Bitcoin wallet can build up dust in it, which is small transactions on the order of 1-100 satoshis, where a satoshi is the smallest unit that a Bitcoin can be divided into. Dust is accumulated due to transactions leaving all but 1 satoshi in a Bitcoin address for example.

Due to network fees, this dust is usually inaccessible, but due to a slowdown in Bitcoin activity fees have recently dropped low enough so that users can profitably consolidate their dust. This is why a Bitcoin user decided to consolidate nearly 100 MB of dust transactions all at once on 15 November.

Fortunately, network activity remained low, so it only took two days for all of these dust transactions to be confirmed and leave the mempool. This shows that the Bitcoin network is currently highly efficient in clearing out large mempool backlogs. is committed to unbiased news and upholding journalistic codes of ethics. For more information please read our Editorial Policy here.

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How to Push Through a Stuck Bitcoin Payment with the Child Pays for Parent (CPFP) Technique

How To Push Through A Stuck Bitcoin Payment With The Child Pays For Parent (CPFP) Technique

In order to understand what Child Pays For Parent (CPFP) is, how it works, and what it is useful for, it is first important to discuss how exactly Bitcoin transactions work. 

How Bitcoin Transactions Work: Confirmations, Transaction Fees, Mempool

When a Bitcoin transaction is sent it starts out as an unconfirmed transaction. On average an unconfirmed transaction receives a confirmation in 10 minutes if an appropriate miners fee is attached. That being said, 10 minutes is just an average confirmation time, and in reality, confirmations can take anywhere from a few seconds to several hours. 

An important caveat that occurs when sending Bitcoin is that the appropriate miners’ fee is constantly fluctuating. Unconfirmed transactions reside in the Bitcoin mempool, and if this mempool becomes overloaded with unconfirmed transactions then the transaction fee rises. Essentially, Bitcoin users who do not want to wait for all of the other unconfirmed transactions to confirm, which could take hours, can set a higher transaction fee so that their transaction is given the highest priority and confirmed in the next block. 

Another way to think about it is that Bitcoin transaction fees are a marketplace, with the supply being the amount of room available in blocks, and the demand being the number of unconfirmed transactions in the mempool. Supply on average remains constant, but demand can increase, forcing Bitcoin transaction fees upwards. 

The most severe episode of mempool congestion occurred in December 2017, a time when Bitcoin hype, speculation, and trading activity was perhaps at its highest point in history so far. Bitcoin transaction fees skyrocketed above USD 50, or about 1,000 satoshis per byte. This was an anomalous event, and since then the highest transaction fees observed were USD 5-10 in late June 2019.

In general, it is quite common to see Bitcoin transaction fees rise above USD 1. Also, Bitcoin transaction fees are often lower than USD 1, sometimes dropping as low as a few cents, which is only a few satoshis per byte. 

The problem is that Bitcoin transaction fees can rapidly fluctuate between a few satoshis per byte to hundreds of satoshis per byte. This transaction fee volatility has become even more amplified since the bull run started in March 2019. 

The number of unconfirmed transactions in mempool between late June and late July 2019, with fees in satoshis/byte, colored. Chart courtesy of Johoe’s Bitcoin Mempool Statistics

A Bitcoin user may attach the proper transaction fee at the time they send, but then maybe it takes a while for the Bitcoin network to find the next block, or a rally starts on the market causing a rapid increase in transaction activity.

In either case, the mempool essentially becomes flooded with unconfirmed transactions, and the Bitcoin user who had attached an appropriate transaction fee only minutes ago realizes that the transaction fee is now far too low.

This can result in an unconfirmed Bitcoin transaction getting stuck for hours or days, which can cause serious problems for Bitcoin ATM and cryptocurrency exchange users since they will not be able to access their money until the mempool clears out and transaction fees drop, which could take a long time. 

One way of lessening the chance of sending a Bitcoin transaction that will get stuck is by keeping track of the Bitcoin mempool at Johoe’s Bitcoin Mempool Statistics. If you check this website before sending a Bitcoin transaction then you will know how much of a transaction fee you have to send to be safe. 

Child Pays for Parent Rescues Stuck Bitcoin Transactions

If that doesn’t work, or you use a low transaction fee by accident, then Child Pays For Parent (CPFP) is a technique that can be used to push through the transaction, rather than waiting for the mempool to clear out. 

A Bitcoin transaction consists of a set of inputs and outputs. For example, if someone has 1 Bitcoin in their wallet and they are trying to send 0.6 Bitcoin, then the 1 Bitcoin is the input, and the output is 0.6 Bitcoin to the receiver’s address, with 0.4 Bitcoin coming back as the change to the sender. CPFP utilizes the change in a Bitcoin transaction. 

Basically, if a Bitcoin transaction is stuck, then another transaction can be sent with the change from the transaction. The original stuck Bitcoin transaction is called the parent, and the new transaction using the change is called the child. 

Bitcoin mining software is not allowed to confirm a child transaction before the parent transaction, so the software aggregates the transactions and averages out the fees across them. Therefore, a much higher fee is added to the child transaction, raising the effective transaction fee for the stuck Bitcoin transaction, allowing the stuck Bitcoin transaction to be confirmed rather than waiting hours or days for the mempool to clear out. 

glad to see CPFP (child pays for parent) finally implemented in #bitcoin

— Stephen Pair (@spair) June 17, 2016

The Bitcoin Core wallet, which is the official Bitcoin wallet, offers the capability to do CPFP. Also, Electrum and the Samurai Wallet are compatible with CPFP.

Coinbase began offering CPFP to users in Fall 2018. If a Bitcoin transaction remains unconfirmed for 4 blocks then Coinbase will send out a child transaction with a high enough fee to push through the stuck parent transaction. This has apparently saved numerous customers from having to wait for hours or days, improving the customer experience at Coinbase. 

Clearly, CPFP is a powerful technique that Bitcoiners should be aware of, since if a Bitcoin transaction ever gets stuck in unconfirmed status, then CPFP can be used to push the transaction through. This increases the efficiency of the Bitcoin economy and improves the Bitcoin experience as users who know how to utilize CPFP will not have to deal with their funds being tied up in an unconfirmed transaction for an extended period of time. Perhaps in the future CPFP will become an option in every Bitcoin wallet, which would create a smoother user experience for everyone and possibly increase Bitcoin adoption. is committed to unbiased news and upholding journalistic codes of ethics. For more information please read our Editorial Policy here.

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Bitcoin Transaction Frequency Increases 50% Since April 2018, Fees Stay Put

Bitcoin transaction frequency has increased roughly 50% since April 2018, yet during the same period of time, transaction fees have not risen. This is likely a demonstration of how SegWit and transaction batching have helped make Bitcoin more scalable.

Estimating daily transaction frequency is somewhat difficult since there is a weekly oscillation of Bitcoin transaction frequency that causes daily frequency to rapidly change. Eyeballing the chart, there were on average 165,000 transactions per day at the beginning of April. This has steadily increased since then to 245,000 in late October 2018, a 48.5% increase. This is just a rough estimate but the point is Bitcoin transaction frequency has just about grown by half its April numbers.

Simultaneously, transaction fees remain close to zero and are not being impacted by increasing transaction frequency. Currently, the fee for confirming within several blocks is less than USD 0.25 per transaction, and this has been the case since early July. In general, since April, transaction fees have actually been decreasing, which may be a sign that SegWit and transaction batching adoption is increasing.

SegWit, short for segregated witness, has a block size limit of 1 million units, rather than bytes like the old system. Signature data, called the witness, is separated from the Merkle Tree and only counts as 1/4 of a unit. This has caused the average maximum block size to increase from 1 mb to 1.2-1.3 mb, with some record block sizes in excess of 2 mb. Allowing more transactions into each block reduces transaction fees, and SegWit adoption is rapidly increasing.

Transaction batching is usually what causes blocks to reach sizes greater than 1.2-1.3 mb. Batching works by merging several Bitcoin transactions into a single one, which saves space. Thousands of transactions can be merged into one transaction via batching.

Looking at Bitcoin block size gives a good indication of how close the network is to reaching maximum capacity, at which point transaction fees will increase. The average daily block size is extremely volatile, and it is hard to estimate an average block size for a week or month but in general, there is an uptrend since April from roughly 0.6 mb to 0.95 mb currently.

Average block size would have to consistently be above 1 mb every day for a surge in transaction fees to occur, unlike the current conditions where average block size is far below 1 mb on most days. The last time block sizes were consistently above 1 mb was in February 2018 on the tail end of the transaction fee crisis which saw fees in excess of USD 30 in December 2017.

At the rate transaction frequency is increasing on the Bitcoin network, eventually, blocks will be filled consistently. However, users will have a bigger incentive to use second layer solutions like Lightning Network at that point, which should prevent a fee crisis.


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