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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92
votes
5answers
23k 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 ...
158
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7answers
115k 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?
76
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6answers
50k 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
56
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6answers
75k 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?
45
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4answers
20k 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 ...
94
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2answers
86k 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 ...
71
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3answers
20k 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?
14
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1answer
5k 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?
28
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3answers
13k 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) ...
41
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4answers
19k views

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

Ethereum.org's introductory Command Line Interface tutorial mentions these clients: eth - a C++ client suitable for mining, IoT and contract development geth - a security audited Go client for use ...
22
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4answers
16k 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?
103
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11answers
80k 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 ...
30
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2answers
27k 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 ...
35
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3answers
63k 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): $...
61
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2answers
14k 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?
33
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5answers
13k 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 ...
46
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2answers
27k 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",...
19
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1answer
3k 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 ...
10
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1answer
779 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 ...
16
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2answers
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 ...
8
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1answer
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 ...
16
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4answers
18k 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 ...
7
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1answer
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 <...
30
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6answers
41k 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=...
7
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1answer
1k 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?
10
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1answer
1k 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?
6
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2answers
6k 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 ...
6
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2answers
5k 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 ...
18
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6answers
24k 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://...
14
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1answer
3k 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 ...
23
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3answers
11k views

Is it possible to cancel a transaction?

Is it possible to cancel a transaction broadcast to the blockchain? Suppose I broadcast a transaction and want to cancel it before it has been mined. Is this possible? This could be useful on ...
2
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1answer
6k 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 "...
10
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2answers
6k 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....
9
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2answers
6k 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. ...
6
votes
1answer
1k 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 ...
6
votes
1answer
2k 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 ...
3
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1answer
1k 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 "...
6
votes
1answer
651 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?
4
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1answer
606 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 ...
1
vote
1answer
347 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 ...
16
votes
1answer
5k 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 ...
13
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3answers
2k views

Is there a functional equivalent to Factom in Ethereum?

Factom is a distributed data and records management and audit system. How easily can what Factom does be done in Ethereum? Are there any working DAPPS doing this? Could a simple smart contract take ...
6
votes
2answers
4k views

Deploying contract from contract

I try something like this: Child.sol pragma solidity ^0.4.6; contract Child { address owner; function Child() { owner = msg.sender; } } Parent.sol pragma solidity ^0.4.6; import "./...
10
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3answers
26k views

Storing document/file in blockchain [duplicate]

I am planning to do a POC on blockchain for uploading and verifying documents. I was wondering if I can store a complete document in blockchain. After some research on net most of the example, I found ...
20
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1answer
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 ...
13
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1answer
8k 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 ...
8
votes
1answer
859 views

What is the composition of the blockchain database?

From axic's explanation of the structure of the ethereum database, we learned that data is stored in Merkle Patricia tries, usually inside a LevelDB store. It consists of structures such as blocks, ...
7
votes
1answer
3k 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?
5
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2answers
1k views

How can we retrieve the evolution of the state of an smart contract variable?

I have a simple smart contract with a variable color which stores a string. If I unterstand correctly, each transaction can change the state of this variable and is stored permanently into the ...
2
votes
2answers
2k views

Where are the variables of a smart contract stored?

we all know that we can write smart contract with solidity in ethereum such as: mapping(bytes32 => bytes32) private userPasswds ; event RecordReturnResult(bool res); /// @dev new the ...