ADR 068: Preblock
Changelog​
- Sept 13, 2023: Initial Draft
Status​
DRAFT
Abstract​
Introduce PreBlock, which runs before begin blocker other modules, and allows to modify consensus parameters, and the changes are visible to the following state machine logics.
Context​
When upgrading to sdk 0.47, the storage format for consensus parameters changed, but in the migration block, ctx.ConsensusParams() is always nil, because it fails to load the old format using new code, it's supposed to be migrated by the x/upgrade module first, but unfortunately, the migration happens in BeginBlocker handler, which runs after the ctx is initialized.
When we try to solve this, we find the x/upgrade module can't modify the context to make the consensus parameters visible for the other modules, the context is passed by value, and sdk team want to keep it that way, that's good for isolations between modules.
Alternatives​
The first alternative solution introduced a MigrateModuleManager, which only includes the x/upgrade module right now, and baseapp will run their BeginBlockers before the other modules, and reload context's consensus parameters in between.
Decision​
Suggested this new lifecycle method.
PreBlocker​
There are two semantics around the new lifecycle method:
- It runs before the
BeginBlockerof all modules - It can modify consensus parameters in storage, and signal the caller through the return value.
When it returns ConsensusParamsChanged=true, the caller must refresh the consensus parameter in the finalize context:
app.finalizeBlockState.ctx = app.finalizeBlockState.ctx.WithConsensusParams(app.GetConsensusParams())
The new ctx must be passed to all the other lifecycle methods.