23
votes
Accepted
UTXO model vs. account/balance model
The choice between the UTXO model and the balance model is primarily one between privacy incentives and apparent intuitiveness.
If one follows the standard advice of not reusing addresses/outputs/...
- 102k
23
votes
Accepted
Why is there "Change" in Bitcoins?
Bitcoin follows a Unspent Transaction Output (utxo) model.
Our modern banking systems follow an account model - you're assigned a bank account number (similar to an address), and send and receive ...
- 16.9k
18
votes
Where is the UTXO data stored?
I assume this question is about Bitcoin Core's internal operations. This description is valid for version 0.8 and later (up to 0.14 at least).
One part of the system deals with the active chain, ...
- 102k
15
votes
Accepted
With 100% segwit transactions, what would be the max number of transaction confirmation possible on a block?
Very interesting question, let's see what the smallest transaction we can build is. For it to be minimal it has to be a single input and a single output. The non-segwit part would look something like ...
- 9,309
13
votes
Accepted
Why is Bitcoin Core using LevelDB instead of Redis or SQLite?
Redis and LevelDB solve very different problems. We tried using SQLite and its performance was abysmal.
Bitcoin Core needs a database to store the set of unspent transaction outputs (UTXOs). This ...
- 102k
11
votes
Why is there "Change" in Bitcoins?
There are a lot of good answers, but I want to point out the most obvious answer.
Say you have 1 bitcoin and you send 0.2 bitcoin to me and the design leaves it so that you still have 0.8 bitcoin in ...
- 51.4k
9
votes
Accepted
How to find all UTXOs?
With vanilla Bitcoin Core, there is no efficient way to do this.
I see two options:
a) Slow and very inefficient RPC loop (not recommended)
Get the genesis block hash (RPC getblockhash 0)
Get the ...
- 6,002
8
votes
Accepted
Why is it not possible to replay transactions?
Transaction inputs use Unspent Transaction Outputs (UTXO).
UTXO are created by transactions. They are uniquely identified by the transaction id and the output position in the transaction that created ...
- 72.6k
8
votes
How to check if an output has been spent?
If gettxout returns something, the output is unspent. If it returns nothing, the output either never existed or is spent.
You do not need -txindex for this.
- 102k
8
votes
Accepted
How is the UTXO database initialized?
The UTXO database starts empty and then is updated while the blockchain is parsed in the manner that you described. Only, there can be more than one input and more than one output for a transaction, ...
- 72.6k
8
votes
Accepted
Do all Tx's have UTXO?
Transactions are money orders to the Bitcoin network that reassign value from one owner to another. To that end, transactions reference pieces of Bitcoin in the inputs and reassign this value to ...
- 72.6k
8
votes
Do UTXO's ever get consolidated to avoid complexitity?
When you pay someone using a number of utxo's to fund your payment, the output being created is a new single utxo with the total amount of all those input (minus change and fees). Effectively, you ...
- 1,854
7
votes
Accepted
Why does bitcoind use a fork of LevelDB for key-value storage?
The fork serves two purposes:
Local modifications that are hard to bring upstream:
Windows support (which is partially based on the existing Windows port, but needed changes for building in MinGW)
...
- 102k
7
votes
What is an "unspent output"?
Bitcoin is a distributed system that enables users to receive, store, and send money. Value is transmitted by submitting a payment order to the network called a transaction. Transactions are ...
- 72.6k
7
votes
Transaction with Multiple Inputs having Same Address
Inputs do not refer to addresses, but rather unspent transaction outputs (UTXOs). If there are multiple UTXOs payable to the same address, then a transaction spending those UTXOs will have to list ...
- 8,822
7
votes
Accepted
Will all UTXOs eventually be worth 1 Satoshi?
Can two UTXOs ever be combined into one UTXO?
Yes, absolutely. Each transaction can have any number of inputs and outputs; it can certainly have fewer outputs than inputs.
Here for example is a ...
- 23k
7
votes
utxo vs account-model
The primary advantages of the UTXO model are simplicity of implementation and improved privacy.
With the UTXO model, transactions just consume some UTXOs and create some UTXOs. This tight constraint ...
- 51.4k
7
votes
Accepted
Do confidential transactions produce an UTXO
In Confidential Transactions (as used in Blockstream's Elements and Liquid), there are still identifiable UTXOs.
The only change is that instead of the amount, a homomorphic commitment to the amount ...
- 102k
7
votes
How bitcoin nodes update UTXO set when their latests blocks are replaced?
Bitcoin Core since v0.8 maintains "undo files" that contain the information necessary to undo the effect of a block on the UTXO set.
In a way you can see blocks as authenticated patches to be applied ...
- 102k
7
votes
Accepted
Best way to find list of UTXO related to xpub
The balance checks are cut short based on a gap limit.
A gap limit is usually set to 20, and is defined as a consecutive block of addresses with no transactions.
Since HD wallets only give out a new ...
- 16.9k
7
votes
Accepted
When does Bitcoin update the UTXO set?
This is implementation dependent, but in Bitcoin Core there is not just a single UTXO set:
The UTXO set on disk in the chainstate/ directory in a database. It corresponds to the state as of the last ...
- 102k
7
votes
Accepted
How is the balance of a Bitcoin address quickly calculated?
At the protocol level, Bitcoin has no concept of "balances" or "addresses", and their common interpretation isn't relevant during verification.
Every transaction spends "coins&...
- 102k
7
votes
How many useable UTXOs are possible with BTC inside them?
There are currently already about 84.3M UTXOs. The consensus rules don't restrict the UTXO set size except that the UTXO set growth is delimited by the available blockspace. The smallest output type ...
- 72.6k
7
votes
Accepted
What was the largest UTXO ever created in bitcoin’s entire history?
No, the largest output ever created was 500,000 BTC:
29a3efd3ef04f9153d47a990bd7b048a4b2d213daaa5fb8ed670fb85f13bdbcf
I used this Blockchair query to find out: https://blockchair.com/bitcoin/outputs?s=...
- 6,668
6
votes
Accepted
How is it possible to say that a bitcoin was fully spent?
An output ("coin") is by definition either fully unspent or completely spent. There is nothing in between. A transaction has one or more inputs (which refer to the unspent outputs of earlier ...
- 6,324
6
votes
Accepted
How long is a Bitcoin?
A bitcoin is not a piece of data, and therefore does not have a length. A bitcoin, the unit of currency, is just like any other unit of measurement. It wouldn't make sense to ask "how much data is a ...
- 8,822
6
votes
Why do some transactions have more than one input?
What might be confusing you, and which is a common misconception, is that the addresses themselves somehow "hold" the bitcoin balances, and gain and lose the coins via transactions. In fact all the ...
- 11.8k
6
votes
Accepted
Why has UTXO set stopped growing since 2017-06-03?
It's hard to know for sure what's been going on. My guess would be it's a mix of :
Better coin selection algorithms used by large wallets (exchanges)
Increase in fees pushed some inefficient services ...
- 1,274
6
votes
Accepted
a few questions about how HD wallet works
1) ...How's my total UTXO calculated?...
Each node calculates it's own UTXO set, there is no single 'global UTOX set'. You may own some subset of the UTXOs, but there is no pooling. If you receive ...
- 18k
6
votes
Accepted
What are the standard formats of transaction outputs?
AFAIK there are 5 different standard non-SegWit transaction types, and 4 SegWit ones.
Non-SegWit:
Pay to public key (P2PK)
PUSH (1 byte) + <compressed/uncompressed_pk> (33/65 bytes) + ...
- 3,192
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