Has something changed recently in testnet? Today I've been seeing new blocks appear every 1-5 seconds instead of the usual 10-20 minutes

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Testnet has a built in functionality that changes the difficulty to 1 if the mining process takes 20 minutes or longer.

This question explains the dropping of difficulty to 1.

So while the difficulty is 1, the blocks are being formed rapidly until the difficulty reaches to a value which takes 10 minutes.

  • It's a bit more subtle than that. Normally when this happens, the difficulty only drops to 1 for the next block. The following block has to be at the regular difficulty, unless another 20 minutes elapse. So this doesn't directly explain blocks every few seconds. I believe this happens when a difficulty-1 block, added under the 20-minute rule, is the last block before a regular difficulty adjustment (every 2016 blocks). In that case the adjustment sets the new difficulty to 1, and this sticks until it adjusts again 2016 blocks later and eventually creeps back up. Commented Feb 18, 2019 at 15:47
  • I think there has been another question explaining this, and I will link it if I can find it. Commented Feb 18, 2019 at 15:47

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