docs: ADR 046 - Module Params (cosmos#10214)

ref: cosmos#9913

---

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docs/architecture/README.md

@@ -81,3 +81,4 @@ When writing ADRs, follow the same best practices for writing RFCs. When writing
 ### Draft
 
 - [ADR 044: Guidelines for Updating Protobuf Definitions](./adr-044-protobuf-updates-guidelines.md)
+- [ADR 046: Module Params](./adr-046-module-params.md)

docs/architecture/adr-046-module-params.md

@@ -0,0 +1,184 @@
+# ADR 046: Module Params
+
+## Changelog
+
+- Sep 22, 2021: Initial Draft
+
+## Status
+
+DRAFT
+
+## Abstract
+
+This ADR describes an alternative approach to how Cosmos SDK modules use, interact,
+and store their respective parameters.
+
+## Context
+
+Currently, in the Cosmos SDK, modules that require the use of parameters use the
+`x/params` module. The `x/params` works by having modules define parameters,
+typically via a simple `Params` structure, and registering that structure in
+the `x/params` module via a unique `Subspace` that belongs to the respective
+registering module. The registering module then has unique access to its respective
+`Subspace`. Through this `Subspace`, the module can get and set its `Params`
+structure.
+
+In addition, the Cosmos SDK's `x/gov` module has direct support for changing
+parameters on-chain via a `ParamChangeProposal` governance proposal type, where
+stakeholders can vote on suggested parameter changes.
+
+There are various tradeoffs to using the `x/params` module to manage individual
+module parameters. Namely, managing parameters essentially comes for "free" in
+that developers only need to define the `Params` struct, the `Subspace`, and the
+various auxiliary functions, e.g. `ParamSetPairs`, on the `Params` type. However,
+there are some notable drawbacks. These drawbacks include the fact that parameters
+are serialized in state via JSON which is extremely slow. In addition, parameter
+changes via `ParamChangeProposal` governance proposals have no way of reading from
+or writing to state. In other words, it is currently not possible to have any
+state transitions in the application during an attempt to change param(s).
+
+## Decision
+
+We will build off of the alignment of `x/gov` and `x/authz` work per
+[#9810](https://github.com/cosmos/cosmos-sdk/pull/9810). Namely, module developers
+will create one or more unique parameter data structures that must be serialized
+to state. The Param data structures must implement `sdk.Msg` interface with respective
+Protobuf Msg service method which will validate and update the parameters with all 
+necessary changes. The `x/gov` module via the work done in 
+[#9810](https://github.com/cosmos/cosmos-sdk/pull/9810), will dispatch Param 
+messages, which will be handled by Protobuf Msg services.
+
+Note, it is up to developers to decide how to structure their parameters and
+the respective `sdk.Msg` messages. Consider the parameters currently defined in
+`x/auth` using the `x/params` module for parameter management:
+
+```protobuf
+message Params {
+  uint64 max_memo_characters       = 1;
+  uint64 tx_sig_limit              = 2;
+  uint64 tx_size_cost_per_byte     = 3;
+  uint64 sig_verify_cost_ed25519   = 4;
+  uint64 sig_verify_cost_secp256k1 = 5;
+}
+```
+
+Developers can choose to either create a unique data structure for every field in
+`Params` or they can create a single `Params` structure as outlined above in the
+case of `x/auth`.
+
+In the former, `x/params`, approach, a `sdk.Msg` would need to be created for every single
+field along with a handler. This can become burdensome if there are a lot of
+parameter fields. In the latter case, there is only a single data structure and
+thus only a single message handler, however, the message handler might have to be
+more sophisticated in that it might need to understand what parameters are being
+changed vs what parameters are untouched.
+
+Params change proposals are made using the `x/gov` module. Execution is done through
+`x/authz` authorization to the root `x/gov` module's account.
+
+Continuing to use `x/auth`, we demonstrate a more complete example:
+
+```go
+type Params struct {
+	MaxMemoCharacters      uint64
+	TxSigLimit             uint64
+	TxSizeCostPerByte      uint64
+	SigVerifyCostED25519   uint64
+	SigVerifyCostSecp256k1 uint64
+}
+
+type MsgUpdateParams struct {
+	MaxMemoCharacters      uint64
+	TxSigLimit             uint64
+	TxSizeCostPerByte      uint64
+	SigVerifyCostED25519   uint64
+	SigVerifyCostSecp256k1 uint64
+}
+
+type MsgUpdateParamsResponse struct {}
+
+func (ms msgServer) UpdateParams(goCtx context.Context, msg *types.MsgUpdateParams) (*types.MsgUpdateParamsResponse, error) {
+  ctx := sdk.UnwrapSDKContext(goCtx)
+
+  // verification logic...
+
+  // persist params
+  params := ParamsFromMsg(msg)
+  ms.SaveParams(ctx, params)
+
+  return &types.MsgUpdateParamsResponse{}, nil
+}
+
+func ParamsFromMsg(msg *types.MsgUpdateParams) Params {
+  // ...
+}
+```
+
+A gRPC `Service` query should also be provided, for example:
+
+```protobuf
+service Query {
+  // ...
+  
+  rpc Params(QueryParamsRequest) returns (QueryParamsResponse) {
+    option (google.api.http).get = "/cosmos/<module>/v1beta1/params";
+  }
+}
+
+message QueryParamsResponse {
+  Params params = 1 [(gogoproto.nullable) = false];
+}
+```
+
+## Consequences
+
+As a result of implementing the module parameter methodology, we gain the ability
+for module parameter changes to be stateful and extensible to fit nearly every
+application's use case. We will be able to emit events (and trigger hooks registered 
+to that events using the work proposed in [even hooks](https://github.com/cosmos/cosmos-sdk/discussions/9656)),
+call other Msg service methods or perform migration.
+In addition, there will be significant gains in performance when it comes to reading 
+and writing parameters from and to state, especially if a specific set of parameters 
+are read on a consistent basis.
+
+However, this methodology will require developers to implement more types and
+Msg service metohds which can become burdensome if many parameters exist. In addition,
+developers are required to implement persistance logics of module parameters.
+However, this should be trivial.
+
+### Backwards Compatibility
+
+The new method for working with module parameters is naturally not backwards
+compatible with the existing `x/params` module. However, the `x/params` will
+remain in the Cosmos SDK and will be marked as deprecated with no additional
+functionality being added apart from potential bug fixes. Note, the `x/params`
+module may be removed entirely in a future release.
+
+### Positive
+
+- Module parameters are serialized more efficiently
+- Modules are able to react on parameters changes and perform additional actions.
+- Special events can be emitted, allowing hooks to be triggered.
+
+### Negative
+
+- Module parameters becomes slightly more burdensome for module developers:
+    - Modules are now responsible for persisting and retrieving parameter state
+    - Modules are now required to have unique message handlers to handle parameter
+      changes per unique parameter data structure.
+
+### Neutral
+
+- Requires [#9810](https://github.com/cosmos/cosmos-sdk/pull/9810) to be reviewed
+  and merged.
+
+<!-- ## Further Discussions
+
+While an ADR is in the DRAFT or PROPOSED stage, this section should contain a summary of issues to be solved in future iterations (usually referencing comments from a pull-request discussion).
+Later, this section can optionally list ideas or improvements the author or reviewers found during the analysis of this ADR. -->
+
+## References
+
+- https://github.com/cosmos/cosmos-sdk/pull/9810
+- https://github.com/cosmos/cosmos-sdk/issues/9438
+- https://github.com/cosmos/cosmos-sdk/discussions/9913