How Stratis Just Broke The Bitcoin Testnet With TumbleBit nopara73 Follow Sep 21, 2017 · Unlisted

I cannot recall any precedent about an altcoin to develop something for Bitcoin. It turns out when this happens and the community suddenly rushes into the Bitcoin testnet to test an experimental technology things break.

It’s all about evil testnet miners

The problem is: testnet miner incentives are misaligned. Since testnet coins are worthless, miners don’t care about putting transactions into a block.

As a result we ended up with 5KB blocks and 5MB testnet mempool.

But it gets worse… It’s not just about putting too few transactions into blocks, but those transactions are selected randomly, not based on fees. Again, because testnet coins are worthless.

Edit: As /u/nullc pointed out it is possible the miners “the miners mining the blocks with transactions simply weren’t running when their transactions were created”. And more closely examining the blocks it seems like they are actually including the high fee transactions, so I was likely wrong on this.

So what will be the TumbleBit test results?

In tumblebit, first the client must open a payment channel with the Tumbler. The transaction is broadcasted, but when the time comes to advance to the next phase, the tumbler sees the channel opening transaction is not confirmed, so the tumbler will leave the client in that phase and continue regardless.

Finally, after some time the client gets refunded.

What kind of transactions we are flooding the mempool with?

For testing we use a Tumbler denomination of 0.002tbtc. So when we see a transaction that has this output, that’s ours.

Consequently, when we see a transaction that spends this output, that’s going to be our TumbleBit transaction, too. This is the refund.

Bigger Boats, Now!

From now on I am a testnet bigblocker. And I will pray for a hero miner who cleans up that rapidly growing testnet mempool by creating big testnet blocks, as Satoshi envisioned.