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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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133 votes
9 answers
41k views

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
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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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115 votes
8 answers
96k 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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68 votes
5 answers
58k views

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
69 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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111 votes
4 answers
111k 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
101 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
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14 votes
1 answer
7k views

What Ethereum blockchain explorers exist?

What blockchain explorers exist and What special features do they have? Are they open-source? How reliable are they (approximate uptime in %)? Is there a testnet version?
Tjaden Hess's user avatar
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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
  • 2,018
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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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
51 votes
13 answers
123k 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
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
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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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85 votes
2 answers
29k 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
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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46 votes
3 answers
84k 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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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
  • 1,378
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
  • 457
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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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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14 votes
1 answer
2k views

How can I reliably induce a blockchain fork for testing purposes?

I would like to reliably induce a fork on a private testnet so that I can test the behavior of off-blockchain code that interacts with contracts. (see related questions as to why I would want to do ...
Paul S's user avatar
  • 4,281
8 votes
1 answer
2k views

How do I tell whether the Mist/Wallet is "fast" or "full" syncing?

I'm currently installing Mist/Ethereum Wallet from the pre-built binaries. Having the run the ./Ethereum-wallet executable, it's now part-way through syncing the blockchain. It seems to be taking ...
Richard Horrocks's user avatar
14 votes
1 answer
3k views

Why do some blocks contain no transactions?

While poking through my Geth logs I noticed that block 1,000,006 doesn't actually contain any transactions. Why is that?
Richard Horrocks's user avatar
8 votes
1 answer
1k views

How is contract storage arranged?

Thinking about smart contract storage, how is the data arranged? I know that every variable within a contract has an unique ID, therefore, it's possible to create a node with a structure like <...
Henrique Barcelos's user avatar
2 votes
1 answer
680 views

State only node

Is it possible for the network clients to just keep the latest network state (without keeping track of the past transactions) while not harming the network security? That is, is it really needed to ...
Jan Beneš's user avatar
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
  • 383
9 votes
1 answer
3k views

Can a contract view the details of a transaction, given a transaction id?

Can a contract view the details of a transaction, given a transaction id? More generally, what details of the blockchain is a given contract aware of?
Fernando Tiberti's user avatar
6 votes
2 answers
6k views

How to create a token smart contract that sends tokens after recieving payment in ether?

Hey everyone I am launching an ICO. I need to create a smart contract that holds a certain amount of tokens that I created. Then when ether is sent to the smart contract address for my token. It will ...
HannibalTheBlack's user avatar
6 votes
2 answers
7k views

How to apply pyethrecover.py on v3 .json/transfor v3 .json to .v1

I'm trying to get pyethrecover.py running via Python on one of my .json files that were created by Ethereum-wallet for Mac. It seems that my .json file is v3 and the pyethrecover.py only works for v1 ...
Dev's user avatar
  • 61
78 votes
9 answers
112k 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, ...
user avatar
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
  • 1,855
23 votes
8 answers
25k 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
  • 331
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
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
13 votes
1 answer
5k views

Why did Ethereum abandon the GHOST protocol?

It says here (minute 24) that Ethereum started with some limited implementation of GHOST, but then abandoned it two weeks after launch. Why was it abandoned?
ripper234's user avatar
  • 685
12 votes
3 answers
2k views

Block header structure change under the Merge to Proof of Stake?

The yellow paper describes the below block header structure: This includes difficulty, beneficiary, mixHash and nonce values. Presumably these will be redundant under Proof-of-Stake. How will the ...
Lee's user avatar
  • 8,558
11 votes
2 answers
8k views

Corruption on data-block while synchronising

My home server's been down for a couple of days while I do some upgrades. I'd had Geth running in one of the terminal windows, but shut it down gracefully using exit before taking the server offline. ...
Richard Horrocks's user avatar
10 votes
2 answers
11k views

How to list all the contracts currently on the blockchain?

I know one way to interact with contracts is, in the geth interface, to use the command: eth.contract(ABI).at(Address) But for this I will need to know the ABI and address of the contract in advance....
Sukhmaninder's user avatar
8 votes
1 answer
3k views

How can I create connected multiple blockchains?

I want to create multiple private blockchains over Ethereum testnet, which need to be somehow connected. Is it possible to have a node on private blockchain that is connected to the another node on ...
eng-gokhan's user avatar
8 votes
1 answer
1k views

Can you execute a contract twice in one block? [duplicate]

If you call a contract with two different tx from different account, can they be executed and mined in the same block? If yes how do you guarantee order and concurrency integrity like deadlocks?
Roland Kofler's user avatar
8 votes
1 answer
24k views

How do fronrunning and sniper bots work?

If you ever traded in defi, you probably have seen coins getting sniped at the very second of their launch and drastically inflating the prices. I assume these bots are written in js, ad using web3 ...
Itsjonie's user avatar
  • 259
7 votes
1 answer
3k views

How to trace state of transactions in ethereum

I have a smart contract of Student Registration. The state changes in the following manner: When Student enters the credential in the form, the state is OPEN. When college registers the student ...
Rahul Sharma's user avatar
  • 1,303
7 votes
2 answers
3k views

Rules on choosing a Solidity version

Is there a rule on using a specific solidity version? I mostly work with 0.8.7 and they sometimes conflict with some Chainlink or Open Zeppelin contracts since they use either v6 or v7. Should I ...
Parteek Singh Jamwal's user avatar
4 votes
1 answer
645 views

Can geth and eth share the same accounts and blockchain?

It appears when I have multiple ethereum clients installed, that they all have their own data, accounts and even their own copy of the blockchain. Is it possible to share accounts and the blockchain ...
q9f's user avatar
  • 32.9k
4 votes
1 answer
13k views

How do you store image in the Ethereum Blockchain efficiently? [duplicate]

I don't think it makes sense to store the "entire image" on the blockchain. I thought it would be better to store a reference to that image, but that means the actual image file will still be in a "...
0xgoku's user avatar
  • 471
3 votes
1 answer
2k views

Dangling hash node ref: too many open files

I'm running two supernodes with the geth client. At peak times they have 500-800 connections and handle around 16GB traffic per hour. This is how I run the node: geth --networkid "1" --identity "...
q9f's user avatar
  • 32.9k
1 vote
1 answer
436 views

On which node smart contract get executed

I have a general question in my mind please do correct me if i am thinking wrong . Suppose if i deploy the smart contract on the ethereum blockchain having a functionality to pay some tokens at ...
Satyam Agrawal's user avatar
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
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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