The FastLane hard fork was implemented on mainnet block 845,000 on April 30, 2021, at 5:30 am GMT. Due to the fork, the Qtum’s block spacing got slashed from 128 seconds to 32 seconds.
This upgrade didn’t create a new coin since it was only used to update features on the blockchain.
Speeding up the protocol happened via the following four upgrades:
As mentioned above, the Fastlane fork’s biggest change was the slashing of the average block spacing from 128 seconds to 32 seconds. In addition, the following parameters were adjusted as a result of the reduction in block spacing:
- Daily block production went up from 675 to 2,700.
- The expected time to block reward also dropped by 4.
- The block size dropped by 4, maintaining the theoretical transactions per second at around 70 TPS.
The difficulty adjustment algorithm for Qtum was adjusted to ensure that the block spacing remains an average of 32 seconds after the speed was increased.
The block reward was dropped from 4 QTUM to 1 QTUM. This ensured that the number of newly minted QTUM produced by the network before and after the upgrade remained constant. Not reducing the block reward would have made the system increasingly inflationary. Also, smaller stakers will see block rewards more frequently.
In preparation for faster blocks, the team updated the staker code. Why was this necessary? If we reduced block spacing to 32 seconds without changing the staker code, the orphan block rate would soar to 200%, significantly affecting network security.
Orphan blocks are perfectly valid blocks that couldn’t enter the main chain. A high orphan-block rate increases the possibility of a fork and reduces network security. Usually, when a network increases its throughput, it directly impacts the orphan block rate. Reducing this rate and improving overall throughput is the holy grail for blockchain networks.
Therefore, the 32-second block speed increase and Staker efficiency optimization are indispensable, and the two together ensure that the block spacing can be reduced without affecting security.
The increase in Staker mining efficiency allows Stakers to keep up with faster blocks and helps reduce orphan blocks. Per our stress tests, the new staker is doing much better in the new circumstances.
So, how has Qtum fared post-Fastlane? Let’s go through some key points:
- The orphan block rate for the original 128 seconds spacing was around 3%. With 32-second spacing, the orphan block rate rose to 20%. This is not significant enough for orphan chain splits, so this is within the acceptable range.
- Reduced block spacing could lead to more smart contract calls, overwhelming the stakers and leading to orphan blocks. We continued to increase the network load and increase smart contract calls. While the average block spacing was shortened to 32 seconds, the orphan block rate in the network remained at 27%, and there was still no obvious fork, which was in line with security expectations.
All-in-all, Team Qtum feels confident enough to declare the FastLane fork a massive success.