How fast and scalable is a Dapp build on ethereum?

Question

I am a beginner to Dapps on ethereum and smart contracts but I wanted to ask three questions on building on top of ethereum.

Firstly, how fast would an Dapp with a token will the transactions per second and the time of a smart contract to be executed the same as the ethereum blockchain.

Secondly, I hear ethereum uses IPFS, like AWS S3, for storage but what will cost to storage data and how fast will can it be uploaded and downloaded, if it was 1 Mb?

Lastly, do need to download the whole ethereum blockchain to be able use a Dapp built on top of ethereum?

I know, there alot of questions but I am just curious and Thank you, in advance, for answering my questions.

Answer 1

1) Speed of your transactions depend partially on your gas usage. You can use https://ethgasstation.info/ to estimate the speeds. One Ethereum block takes about 15 seconds, so on average you need to wait something like 15/2 seconds for the block to be mined which includes your transaction. Whether your transaction is mined in the very next block depends on network congestion and your gas settings (how much you're willing to pay).

The amount of time your transaction takes depends mostly on when miners decide to include it in a block. Miners prefer transactions which have the best profit/effort ratio (gas price). So it's not so much dependent on your gas usage but on how much you're willing to pay per gas unit.

If the network is congested it means there are more transactions than what miners have time to mine (adjusted by the global mining difficulty settings). In theory that leads to more miners joining the network which again reduces congestion. The idea also somewhat works except when there are sudden spikes in network usage.

2) Ethereum does not use IPFS as such. IPFS is one option for storing data and is quite popular among Ethereum Dapp developers because Ethereum itself is quite bad for storing data inside its blockchain (it's very expensive).

3) Running your own node is one option to access the blockchain (downloading the whole blockchain or a fast mode of some sorts which downloads only part of it). Or you can use an external provides such as Infura which gives you access to the blockchain.