Internal of Diff Calculation

Diff calculation is the core of the diff command. It is responsible for calculating the difference between two versions of a container.

Three modes of diff calculation

1. Checkout Mode

This is the most general mode of diff calculation. It can be used whenever a user want to switch to a different version. But it is also the slowest mode. It relies on the ContainerHistoryCache, which is expensive to build and maintain in memory.

2. Import Mode

This mode is used when the user imports new updates. It is faster than the checkout mode, but it is still slower than the linear mode.

• The difference between the import mode and the checkout mode: in import mode, target version > current version. So when calculating the DiffCalculator doesn't need to rely on ContainerHistoryCache, except for the Tree container.
• The difference between the import mode and the linear mode: in linear mode, all the imported updates are ordered, no concurrent update exists. so there is no need to build CRDTs for the calculation

3. Linear Mode

This mode is used when we don't need to build CRDTs to calculate the difference. It is the fastest mode.