[Ethereum] Is it possible to start Ethereum Wallet in –light mode by default on the Mac

geth and parity have differents methods to save the ethereum blockchain in their internal format. I made many benchs because i find it so long just to use a Wallet.

The pruning mode is how the block data are saved. With the archive mode, all states are saved. So, you know the state at each moment without to reload all the blockchain. With fast and light, we assume that we don't need all this information but only the current state and few before, so we remove many intermediates states.

On geth, the --fast method saves a state of the blockchain at block B[-1500] and all the states after this block (B[-1] is the last block, B[-2] is the before last block ...). So it is possible to rewind at the state of 1500 last blocks. With a full blockchain, you can do it for all blocks.

In parity, there are 4 pruning modes or journalDB algorithms:

• Archive (Archive): as geth Archive we keep all states
• Fast (OverlayRecent): as geth Fast we keep all the full states of the B[-i] blocks
• Light (EarlyMerge): we keep all the states of the B[-i] blocks but in differential (so it is smaller than fast but slower access)
• Basic (RefCounted): we keep all the states of the B[-i] blocks like with OverlayRecent but we remove states after x changes... so we have only the xth last changes

Benchmarks done on i7 3720QM 16GB ram with Geth 1.4.4 (Homestead with 1.6Mi blocks)

_____________________________________________
| Option | Disk Used | Time | Disk Written  |
|--------|-----------|------|---------------|
| none   | 19.GB     | 5h00 | 1TB           |
| fast   | 3.7GB     | 1h00 | 100GB         |
---------------------------------------------

Benchmarks done on i7 3720QM 16GB ram with Geth 1.5.0 unstable (Homestead with 1.6Mi blocks found at https://gitter.im/ethereum/go-ethereum?at=574d26c010f0fed86f49b32f)

__________________________________________________
| command     | Disk Used | Time | Disk Written  |
|-------------|-----------|------|---------------|
| geth        | 21GB      | 5h00 | 150GB         |
| geth --fast | 4.2GB     | 21m  | 35GB          |
| geth export | 1.5GB     | 10m  |               |
| geth import | 21GB      | 3h30 |               |
--------------------------------------------------

Benchmarks done on i7 3720QM 16GB ram with Parity 1.2 (Homestead with 1.6Mi blocks)

_____________________________________________
| Option | Disk Used | Time | Disk Written  |
|--------|-----------|------|---------------|
| archive| 19.GB     | 2h00 | 300GB         |
| fast   | 3.7GB     | 1h30 | 20GB          |
| light  | 2.5GB     | 2h00 | 130GB         |
---------------------------------------------

Note: When you have a node with a blockchain, you can dump the chaindata of geth directory to use it with your other computers. I check it with Linux, Windows and OS X.

Note: if you use --cache with 1024, it could be faster. But it is not significant on my system. The same goes for the --jitvm

Note: the ethereum blockchain saved the final state after transactions but it is safer to replay the transactions to check them.

The geth install bundled with Mist can't be accessed via "geth" on the command line. Here's what worked for me to get Mist to run as a light client.

Install geth separately. On Ubuntu:

sudo apt-get install software-properties-common
sudo add-apt-repository -y ppa:ethereum/ethereum
sudo apt-get update
sudo apt-get install ethereum

On Mac it should be:

brew update
brew tap ethereum/ethereum
brew install ethereum

Now run geth from the command line in light mode:

geth --syncmode "light" --cache 1024

Once that starts, open up Mist normally and it should connect to the geth light instance automatically. The first time you do this it will redownload the entire blockchain and put it in a separate folder. For me on Ubuntu this is ~.ethereum/geth/lightchaindata whereas the normal chaindata is ~.ethereum/chaindata. The first time will take a couple of minutes to redownload the blockchain (but it's much faster than normal) and after that, it should sync up to the chain in a few seconds.