Questions tagged [blockchain]

The Ethereum blockchain is a distributed database based on the Ethereum whitepaper specification and stores both the full transaction list and the most recent state.

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172 votes
8 answers
131k views

What are the Ethereum disk space needs?

How fast is Ethereum blockchain growing and how big is it likely to get in the future? Is it still about 1 GB per month? Are there any data pruning or compression algorithms in place or planned to be ...
Domchi's user avatar
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133 votes
9 answers
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How can a contract run itself at a later time?

In my blockchain application, I would like to have an event triggered at a later time, hours or perhaps even days after the application has most recently received a transaction from a user. How can I ...
Jeff Coleman's user avatar
118 votes
11 answers
84k views

How would I explain Ethereum to a non-technical friend?

I've recently attempted to explain Ethereum to several non-techy friends. My explanation usually involves starting with a comparison to Bitcoin, but this quickly becomes complicated as I then have ...
Richard Horrocks's user avatar
115 votes
8 answers
95k views

Ethereum block architecture

Where can I find a description (preferably a diagram like below) showing the block structure in an Ethereum blockchain? Credits: Wikipedia
zanzu's user avatar
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111 votes
4 answers
110k views

What is Geth's "fast" sync, and why is it faster?

One of the answers to this question suggested using Geth's --fast flag to help quickly synchronise the block data. How does the flag work, and how does using it speed up the synchronisation? Are we ...
Richard Horrocks's user avatar
100 votes
3 answers
38k views

What is an uncle/ommer block?

The Ethereum blockchain is described as containing "ommer" blocks, usually called "uncle" blocks by the general public. What is an ommer/uncle block, and why are they needed?
Jeff Coleman's user avatar
83 votes
2 answers
28k views

ELI5 How does a Merkle-Patricia-trie tree work?

I understand that Merkle tree are Hashes of Hashes, they have the advantage that you can verify only a subtree. But what about Patricia? What does a trie mean? And how is it used in Ethereum?
Roland Kofler's user avatar
77 votes
9 answers
109k views

How to get a contract's balance in Solidity?

How do I get the balance of a contract with solidity? I know geth has web3.eth.getBalance(), but that's to get the contract balance after it has been deployed. Is there a standard way of doing this, ...
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68 votes
6 answers
105k views

What number of confirmations is considered secure in Ethereum?

In Bitcoin, 6 confirmations are considered secure (very low probability of transaction/block reversal). What is the current number in Ethereum?
eth's user avatar
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68 votes
5 answers
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What is the cost to store 1KB, 10KB, 100KB worth of data into the ethereum blockchain?

Whatever is stored in the blockchain is immutable which means I can fetch this data back in the future. As of today (2016-feb), How does one store a 1kb, 10kb, or 100kb or arbitary data/text in the ...
Patoshi パトシ's user avatar
56 votes
3 answers
38k views

What is an Event?

What is an Event? Are they only used in Solidity? How are events defined? How are events initiated? Is there a standard term for an event's invocation (do you say an event "happened", "was called",...
Lee's user avatar
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50 votes
13 answers
120k views

How to decode input data from a transaction?

I'm sending a transaction to an account with some data with the following command: eth.sendTransaction({from:eth.accounts[0],to:eth.accounts[1],value:web3.toWei(1,"ether"),data:web3.toHex("http://...
FrenchieiSverige's user avatar
49 votes
5 answers
29k views

What exactly is an Ethereum client and what clients are there?

What exactly is an Ethereum client? Is it a full network node that can post transactions to the blockchain (if that is the correct lingo?) or could it also be a light JS client that connects from a ...
hcvst's user avatar
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46 votes
3 answers
83k views

How to delete or reset the blockchain in geth? (OSX)

I have a currupt Blockchain and want to hard reset the chain. what do I need to delete in order to start downloading the chain from scratch? I know that there are 2 ethereum folders (I am on OSX): $...
xpnimi's user avatar
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42 votes
4 answers
57k views

Is it possible to cancel a transaction?

Is it possible to cancel a transaction after it has been broadcasted, but before it has been mined? This could be useful on sending an erroneous transaction containing invalid data.
Shuzheng's user avatar
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40 votes
3 answers
32k views

What does it mean that Ethereum is "turing complete"

People often say that Ethereum is a "turing complete" blockchain, or that it comes with a built-in "turing complete" programming language. What does this mean, and why is it an important feature for ...
Josh Stark's user avatar
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40 votes
5 answers
41k views

How can I store data in ethereum blockchain

I want to store pdf hash in blockchain I already read this post What are some proposed ways of storing data in Ethereum? But I'm beginner in this domain and I don't understand... Is it possible to ...
wxcvbn's user avatar
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38 votes
6 answers
48k views

How long is the first sync supposed to last?

I've been running Geth (latest version) for around 12 hours and it's still not finished. The command prompt shows this : INFO [05-21|12:05:00] Imported new chain segment blocks=1 txs=...
J. Doe's user avatar
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38 votes
5 answers
15k views

Exploring and Analyzing the Ethereum blockchain

I would like to explore the data inside of the Ethereum blockchain. All transactions and contracts of the Ethereum Blockchain are stored there. So it's an interesting open dataset and I'd like to get ...
wacax's user avatar
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36 votes
6 answers
36k views

Can I download the whole blockchain from somewhere?

Bitcoin used to offer sharing/downloading a bootstrap.dat which contains the whole blockchain. Are there alternatives to getting it trickling through the peer-to-peer network? Can I just download it ...
Donavan Theodor's user avatar
32 votes
4 answers
14k views

How to create a Dapp from scratch on Ethereum?

Let's say we have someone who knows about blockchain but who doesn't have any background in blockchain-based application. That person wants to code an ethereum-based Dapp (decentralized application) ...
SajZ's user avatar
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29 votes
7 answers
22k views

What are the differences between Bitcoin blockchain and Ethereum blockchain?

Ethereum has been debated in the bitcoin ecosystem and was criticized. In order to understand better both projects, what are the main differences between BTC and ETH regarding the blockchain ...
nelruk's user avatar
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28 votes
3 answers
10k views

What is a Shard?

Proof of Stake brings new concepts to the Blockchain ecosystem. In the dictionary "Shard" is defined as "A broken piece or fragment, as of pottery or glass".
Jmiehau 's user avatar
28 votes
4 answers
34k views

Possible to store the blockchain in a different directory?

I'm running geth on Linux within a Chromebook. The blockchain is being stored within ~/.ethereum, along with other important files. Problem is, the storage capacity on my Chromebook is quite limited ...
FugueWeb's user avatar
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26 votes
6 answers
36k views

What is address(this) in solidity?

As per my understanding contract`s own address is the address which we assign to owner of contract using msg.sender. But I saw this question on SE where it was described that a contract can access its ...
Anam Nizami's user avatar
25 votes
2 answers
9k views

Relationship between Transaction Trie and Receipts Trie

Reading through the Yellow paper, I can see that each block header includes the Keccak 256 hash of the root of the trie for transactions and transaction receipts. I am struggling to understand how and ...
Lee's user avatar
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24 votes
3 answers
28k views

How can i tell if geth is done running?

Well i am new trying to mine and i did the "C:>geth --rpc" and its still going how will i know when its done? i did all the steps leading to this but my pc just keeps running the INFO [05-18|23:32:...
Gilbert's user avatar
  • 241
24 votes
1 answer
2k views

What would be needed to store the blockchain as a IPFS object?

In Christian Lundkvists blog post about possible uses for IPFS, he suggests that storing the Ethereum blockchain as an IPFS object could potentially decrease the size of the chain: We see the ...
MrChico's user avatar
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23 votes
4 answers
17k views

How can I empty the blockchain?

I am trying to do a fast sync using geth --fast but I am getting this message: blockchain not empty, fast sync disabled How can I empty the blockchain to allow for fast sync?
Randomblue's user avatar
  • 2,600
23 votes
2 answers
4k views

Difference between a pruned and unpruned blockchain

At the Berlin Blockchain Meetup, Gustav Simonsson teased the Homestead release coming soon (tm) and we were discussing blockchain bloat and the current size of the Ethereum blockchain. We discussed ...
q9f's user avatar
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23 votes
4 answers
16k views

Error "no key for given address or file" when unlocking coinbase account

Using json-rpc eth_unlockAccount() method I can unlock everyone of my node accounts except coinbase. When trying to unlock coinbase account, geth responds with the message: no key for given address ...
Juan Ignacio Pérez Sacristán's user avatar
22 votes
7 answers
22k views

Computing the Uniswap V3 pair price from Q64.96 number

I am trying to compute a Uniswap V3 pool token price in Solidity. I can get the square root price of Q64.96 number as uint160 (e.g., 1234217676608908277512433764 - value of DAI/ETH pool (price at that ...
pipip's user avatar
  • 321
22 votes
1 answer
3k views

This image claims you can build "decentralized apps", and each computer "contributes a little to process it". Is that claim correct?

This image claims that you can put decentralized apps (say, a messaging program) on the Ethereum network. It also claims that each computer on the network contributes a little bit to the processing of ...
MaiaVictor's user avatar
  • 3,177
21 votes
6 answers
33k views

How to find contract's address?

I successfully setup a private blockchain and created the "hello world" contract according to tutorial from etherium web site. One thing that I can't figure out is how to find the contract later. I ...
user3280964's user avatar
21 votes
1 answer
19k views

Getting private keys of geth accounts

Just the opposite of this question How to import a plain private key into geth or Mist? I would like to know how can I obtain the private keys of the accounts created with geth in this way: $ geth --...
Juan Ignacio Pérez Sacristán's user avatar
20 votes
8 answers
22k views

Question on the terms 'distributed' and 'decentralised'

I am writing a paper on distributed ledger technologies, an umbrella term I have borrowed to put everything that has any relation to blockchains and distributed consensus. Under this umbrella term I ...
pn7a's user avatar
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19 votes
3 answers
15k views

Retrieve CHAIN_ID of the executing chain from a Solidity contract

Is there a way to directly be able to retrieve CHAIN_ID information about the executing chain from a smart contract? I know that for any chain that has EIP-155 implemented, CHAIN_IDs are retrievable ...
Shiri's user avatar
  • 786
19 votes
1 answer
8k views

Usage of memory, storage and stack areas in EVM

In solidity contracts, I can understand that based on variable usage and expensiveness, I can determine that which one should use (memory, storage or stack). But I faced some situations where only ...
Abhishek's user avatar
  • 800
18 votes
5 answers
4k views

What is a blockchain? What is the concept behind it? [closed]

I have been going through some docs, and I understand that BlockChains are mostly like the building blocks in an Ethereum network. So, can someone give a dumbed down explanation/definition about what ...
Dawny33's user avatar
  • 2,007
18 votes
6 answers
14k views

Best way to test a smart contract

I just want to deploy and call a simple sample smart contract only for testing purpose. Do I need to download the entire ethereum blockchain? Its too huge and takes too long to download. Can someone ...
Ashish Sinha's user avatar
18 votes
1 answer
4k views

What is state-trie pruning and how does it work?

Several sources mention the idea of state-trie pruning. What is that, and is it currently being implemented on the network? Is this a manual process or can it be done automatically? If Ethereum is ...
high110's user avatar
  • 4,756
18 votes
4 answers
40k views

Setup Ganache with Metamask. What and where is a Chain ID?

I am following these instructions. The problem is that the above instructions don't mention Chain ID and it appears Chain ID is required to even make it work. Thus, I'm stuck. What is the Chain ID? ...
GN.'s user avatar
  • 633
18 votes
2 answers
13k views

In Mist browser how can I move the data (blockchain) to another drive on Mac OSX?

My Mac "System" drive is almost full. As I actually have two drives, I want to move the blockchain from the default location to the second drive. How can I do it ?
Maksim Ravnovesov's user avatar
18 votes
2 answers
21k views

EthereumJS: How to get public key from private key

I am trying to create a private key and its corresponding public key using EthereumJS library. So far so good I've been able to create private keys using keythereum.create() method. Nevertheless I ...
Juan Ignacio Pérez Sacristán's user avatar
17 votes
3 answers
6k views

Why do we need both nonce and mixhash values in a block?

Looking over the sample genesis blocks, I notice that both nonce and mixhash values can be assigned independent values. Reading the yellow paper it's mentioned that: mixhash: is a 256 - bit hash ...
Sebi's user avatar
  • 5,284
17 votes
3 answers
22k views

'authentication needed: password or unlock' Error when trying to call smart contract method via web3

I am trying to call the smart contract method (deployed on remote ethereum account) from my nodejs DAPP, and getting the following error- Error: authentication needed: password or unlock at ...
rsingh's user avatar
  • 171
17 votes
1 answer
6k views

What does it mean to "run code on the blockchain"? Wouldn't blockchain become huge?

More technically speaking, what does it mean to "run code on the blockchain"? Does it mean that we store the source code and then every full node runs that source code several times? If, for ...
MaiaVictor's user avatar
  • 3,177
17 votes
2 answers
10k views

How much faster is it to sync with --jitvm?

geth help has: VIRTUAL MACHINE OPTIONS: --jitvm Enable the JIT VM The impact of --jitvm has been unanswered and I'm looking for answers to these 3 specifically: How much faster is geth --fast -...
eth's user avatar
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17 votes
9 answers
17k views

The endpoint returned a different chain ID: 0x539 (Ganache)

I am trying to connect Metamask to ganache by creating a custom RPC with the following details: New RPC URL: HTTP://127.0.0.1:7545 Chain Id: 5777 But I keep getting the error message The endpoint ...
Chidi Nkwocha's user avatar
17 votes
4 answers
10k views

If a blockchain is a distributed database, where is the data?

There are a lot of articles describing how Ethereum is just another database, and a number of posts here on this site that talk about storing data on the blockchain itself (e.g., [1], [2]). However, ...
eykanal's user avatar
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