Bitcoin XT's Scaling Implementation Plan and Its Impact

The BITCOIN XT version was launched by Gavin Andresen and Mike Hearn, aiming to solve the problem of 1M block capacity being too small, but its future is uncertain because the other three Bitcoin core developers did not agree and many Bitcoin companies did not explicitly agree.

1. BITCOIN XT expansion plan

Starting from 2016-01-11 00:00:00 UTC, the upper limit of the starting block is 8M.
As time goes by, the block limit gradually increases, and the calculation formula is as follows:

time_start = 1452470400 //Start time, i.e. 2016-01-11 00:00:00 UTC
time_double = 60*60*24*365*2 //two years
size_start = 8000000 //Starting block upper limit 8M

If the block time is greater than 2036-01-06 00:00:00 UTC, size_start* 2 ^10 = 8192M is returned, that is, the maximum block size is 8192M.

If the block time is between 2016-01-11 00:00:00 UTC and 2036-01-06 00:00:00 UTC, the block cap is calculated using the following formula:

The time interval between the block and the start time (seconds) time_delta = block_timestamp – time_start
The difference between the block and the start time is an integer number of two years. Doublings = time_delta / time_double
When the difference between the block time and the start time is an integer of two years, the block upper limit doublings_size = size_start * 2^doublings

The difference between the block and the start time within two years (in seconds) remainder = time_delta % time_double

The capacity of the block should increase within two years from the start time interpolate = (size_start * 2^doublings * remainder) / time_double
Block upper limit max_size = doublings_size + interpolate

The above formulas are combined as follows:

 max_size = size_start * 2^((block_timestamp - time_start) / time_double) * ( 1+ ((block_timestamp - time_start) % time_double)/time_double)

Calculation results:

(1) Starting from 2016-01-11 00:00:00 UTC, the upper limit of the starting block is 8M.
(2) The block limit doubles every two years. For example, on January 11, 2018, the block limit was 16M; on January 11, 2020, the block limit was 32.
(3) As of 2036-01-06 00:00:00 UTC, the maximum block size will be 8192M and will remain unchanged thereafter.

2. Implementation method of BITCOIN XT expansion plan

If the mining pool uses the BitcoinXT node, the mined blocks will use the new version number to tell other miners in the Bitcoin network that you already support XT.
When more than 750 of the most recent 1000 blocks are blocks with new version numbers, the expansion condition is met, leaving two weeks as a buffer. Two weeks later, blocks larger than 1MB will be generated, and the generation time of large blocks will be no earlier than 2016-01-11 00:00:00 UTC. That is, if 75% of the new blocks are generated and it is not 2016-01-11 00:00:00 UTC after two weeks, the generation of large blocks will be postponed to 2016-01-11 00:00:00 UTC.

If it has not reached 75% by 2016-01-11 00:00:00 UTC, continue waiting;
If you never reach 75%, then wait forever.

Once a block larger than 1M is generated, it will be rejected by the Bitcoin Core node, which will cause a fork.

3. The possible impact after BITCOIN XT takes the lead

(1) The number of nodes will be further reduced. Currently, there are 6,000 nodes. The emergence of large blocks makes the maintenance cost higher and higher, and the possibility of enterprise maintenance is increasing. This will lead to the centralization of nodes, that is, all nodes are controlled by hundreds of Bitcoin companies.

(2) Mining is centralized. The emergence of large blocks will lead to the emergence of a large number of super nodes (high configuration, low latency, and high network speed), which is more conducive to the transmission of large blocks and has a greater chance of winning in the block competition, thus further increasing the mining cost.

(3) Large block attack: The transaction verification and confirmation time of large blocks is significantly increased, which consumes a lot of node computing power. Malicious users can construct some large blocks to make many nodes busy and have no time to take care of normal blocks.

(4) The set of unspent transactions will increase significantly, which will take up more node memory.