Topic: Interesting behaivor of TESTNET difficulty (Read 403 times)

They are worthless because you can not trade Bitcoin Testnet on exchanges but in aspect of Bitcoin miners and developers, they are very valuable.

In aspect of development, Bitcoin testnet help developers a lot.
In aspect of Bitcoin users, it is helpful too because they can practice with Testnet without capital loss.

More interesting, in aspect of Bitcoin miners, they have to spend cost, ASICs to mine Bitcoin testnet that actually has intrinsic value input.

Jameson Lopp wrote about that, x4 difficulty and why 1 difficulty is regularly occurs for testnet blocks.

functionality for developers to run "signet" test networks that don't use mining at all, but rather use a federation of block signers

You can see this most recently happening just a couple of months ago at epoch 1,212. Epoch 1,211 took 12 days, 2 hours, and 42 minutes. This is 290.7 hours, which would be 1744.2 blocks. 2015/1744.2 = 1.156. And so if you look at the difficulty for epoch 1,212, it is 1 * 1.156 = 1.156.

It's interesting to see that this happened before. Actually, it's very regular and happens many times a year. Here is the data from 2020 till today.

It's interesting to see that this happened before. Actually, it's very regular and happens many times a year.

The probability for this phenomenon should be a function of the likeliness of a 20-minute block time at the current difficulty and hash rate, at the end of each epoch.

Wait a minute, don't we already have thousands of such useless coins out there and some people even pay for them in hopes of profit?  It's a sad story really.

If someone wants test net coins for development purposes, why do they use the same test coins? They can fork and mine trillions of such coins.

Historically speaking there are times when some miners with a bunch of ASIC miners use their computing power to mine on TestNet. Since the difficulty is low most of the times, their hashrate is more than enough to mine a large number of blocks in a very short time.

To compare, the current difficulty in TestNet is 1024 while on MainNet it is 54,150,142,369,480.
https://blockchair.com/bitcoin/testnet
https://blockchair.com/bitcoin

P.S. regarding the worthlessness of tbtc I have to say in the past there have been some scams involving these coins that gave them kind of a value. Some were big and led to migration to the version 3 TestNet (the current chain) and some were smaller like the last time they were swapping shittokens on token platforms like ethereum with tbtc effectively giving them a value.
This may be the reason for a couple of these hashrate spikes we saw in the past.

The difficulty will reset to 1 if the time since the last block is more than 20 minutes. There is no stipulation that after a difficulty reset block that the next block must be the normal difficulty; if the next block is more than 20 minutes after the current block, then it can also have a difficulty of 1.

For blocks that are found within 20 minutes of each other, the block's difficulty will be the same as the difficulty of the last block in the difficulty interval whose difficulty was not 1 OR the difficulty of the first block in the difficulty interval. This behavior is defined here: https://github.com/bitcoin/bitcoin/blob/master/src/pow.cpp#L32.

The way that the difficulty retarget works is that, at the beginning of the new difficulty interval, the difficulty of the first block in that interval takes the difficulty of the last block in that interval and multiplies that by the time it took to mine the 2016 blocks and then divides it by the target time. The result is then clamped to be at least 1. Since this is based upon the difficulty of the last block in the previous interval, if that block is difficulty 1, then the next interval will also have a difficulty of one.

So what we are seeing here is that the last block in the interval is found 20 minutes after the block before it so it has a difficulty of one. Because the next block adjust the difficulty and it only looks at the block before it (which is difficulty 1), the difficulty of the next interval is 1. So the next 2016 blocks are mined at difficulty 1, and the difficulty then slowly adjusts up again.

There is cap on how much it can rise (or fall) in each adjustment because if the time is smaller (or bigger) than a quarter of (or bigger than 4x) 2 weeks in seconds, it will fall down to default 302,400 (or 4,838,400) sec.

Every block since then has been mined in seconds, and the difficulty is slowly adjusting back upwards to a normal value.

A while ago, I saw a computation of the energy cost to mine 1 testnet coin, and it was quite high. I guess the drop in difficulty is related to the number of coins in circulation being very close to 21 million, and the block reward is 300 times lower than Bitcoin mainnet. This also shows a 51% attack is easy, it looks more like a 99% attack.

if no block has been found in 20 minutes, the difficulty automatically resets back to the minimum for a single block, after which it returns to its previous value.

To compare, the current difficulty in TestNet is 1024 while on MainNet it is 54,150,142,369,480.

But something change in the difficult of testnet in the last hours, somebody is mining like 5 blocks per second, so if someone wants to learn how to mining they can try Testnet on this momment.

the bug was exploited on Bitcoin testnet, causing any nodes still running Bitcoin Core 0.14.x to crash and nodes running 0.15.0 to 0.16.2 to accept a transaction that spent the same funds more than once. When testnet miners managed to produce a valid chain with more proof-of-work than the invalid chain, those non-upgraded nodes attempted to switch to the new chain but were unable to fully un-spend a double-spent input.