Understanding shared state cache
The default behavior of Poky is to build everything from scratch unless BitBake determines that a recipe does not need to be rebuilt. The main advantage of building everything from scratch is that the result is fresh, and there is no risk of previous data causing problems. However, rebuilding everything requires computational time and resources.
The strategy to determine whether a recipe must be rebuilt is complex. BitBake tries to track as much information as possible about every task, variable, and piece of code used in the build process. BitBake then generates a checksum for the information used by every task, including dependencies from other tasks. In summary, BitBake recursively tracks used variables, task source code, and dependencies for the recipes and their dependencies.
Poky uses all this information provided by BitBake to store snapshots of those tasks as a set of packaged data, generated in a cache called the shared state cache (sstate...
