Ethereum private network mining - bitcoin

Question

1) I setup a private ethereum network using the following command
$geth --genesis <genesis json file path> --datadir <some path to an empty
folder> --networkid 123 --nodiscover --maxpeers 0 console
2) Created an account
3) Then, started the miner using miner.start() command.
After a while ethers were getting added automatically to my account, but I don’t have any pending transaction in my private network. So from where could my miners are getting the ethers?
Even though, I didn’t instantiate any transactions in my network, I could see the some transaction being recorded in the logs, once I start the miner.
The log is as follows:
I0118 11:59:11.696523 9427 backend.go:584] Automatic pregeneration of ethash
DAG ON (ethash dir: /Users/minisha/.ethash)
I0118 11:59:11.696590 9427 backend.go:591] checking DAG (ethash dir:
/Users/minisha/.ethash)
I0118 11:59:11.696728 9427 miner.go:119] Starting mining operation (CPU=4
TOT=5)
true
> I0118 11:59:11.703907 9427 worker.go:570] commit new work on block 1 with 0
txs & 0 uncles. Took 7.109111ms
I0118 11:59:11.704083 9427 ethash.go:220] Generating DAG for epoch 0 (size
1073739904) (0000000000000000000000000000000000000000000000000000000000000000)
I0118 11:59:12.698679 9427 ethash.go:237] Done generating DAG for epoch 0, it
took 994.61107ms
I0118 11:59:15.163864 9427 worker.go:349]
And my genesis block code is as follows:
{
“nonce”: “0xdeadbeefdeadbeef”,
“timestamp”: “0x0”,
“parentHash”:
“0x0000000000000000000000000000000000000000000000000000000000000000”,
“extraData”: “0x0”,
“gasLimit”: “0x8000000”,
“difficulty”: “0x400”,
“mixhash”:
“0x0000000000000000000000000000000000000000000000000000000000000000”,
“coinbase”: “0x3333333333333333333333333333333333333333”,
“alloc”: {
}
}
Since my network is isolated and have only one node (no peers), I am quite confused with this behaviour. Any insights would be greatly appreciated.

Answer 1

Your client is mining empty blocks (containing no transactions) and getting rewards for mined blocks what is 5 ETH per block.
If you want to prevent empty block in your private blockchain you should consider using eth client (C++ implementation).
In case of geth client you can use a JavaScript script that will modify client's behavior. Any script can be loaded with js command: geth js script.js.
var mining_threads = 1
function checkWork() {
if (eth.getBlock("pending").transactions.length > 0) {
if (eth.mining) return;
console.log("== Pending transactions! Mining...");
miner.start(mining_threads);
} else {
miner.stop(0); // This param means nothing
console.log("== No transactions! Mining stopped.");
}
}
eth.filter("latest", function(err, block) { checkWork(); });
eth.filter("pending", function(err, block) { checkWork(); });
checkWork();

Answer 2

You can try EmbarkJS which can run geth client with mineWhenNeeded option on private network. It will only mine when new transactions come in.