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Pool Manager Module

The poolmanager module exists as a swap entrypoint for any pool model that exists on the chain. The poolmanager module is responsible for routing swaps across various pools. It also performs pool-id management for any on-chain pool.

The user-stories for this module follow:

As a user, I would like to have a unified entrypoint for my swaps regardless of the underlying pool implementation so that I don't need to reason about API complexity

As a user, I would like the pool management to be unified so that I don't have to reason about additional complexity stemming from divergent pool sources.

We have multiple pool-storage modules. Namely, x/gamm and x/concentrated-liquidity.

To avoid fragmenting swap and pool creation entrypoints and duplicating their boilerplate logic, we define a poolmanager module. Its purpose is twofold:

  1. Handle pool creation
    • Assign ids to pools
    • Store the mapping from pool id to one of the swap modules (gamm or concentrated-liquidity)
    • Propagate the execution to the appropriate module depending on the pool type.
    • Note, that pool creation messages are received by the pool model's message server. Each module's message server then calls the x/poolmanager keeper method CreatePool.
  2. Handle swaps
    • Cover & share multihop logic
    • Propagate intra-pool swaps to the appropriate module depending on the pool type.
    • Contrary to pool creation, swap messages are received by the x/poolmanager message server.

Let's consider pool creation and swaps separately and in more detail.

Pool Creation & Id Management​

To make sure that the pool ids are unique across the two modules, we unify pool id management in the poolmanager.

When a call to CreatePool keeper method is received, we get the next pool id from the module storage, assign it to the new pool, and propagate the execution to either gamm or concentrated-liquidity modules.

Note that we define a CreatePoolMsg interface: https://github.com/osmosis-labs/osmosis/blob/f26ceb958adaaf31510e17ed88f5eab47e2bac03/x/poolmanager/types/msg_create_pool.go#L9

Each balancer, stableswap and concentrated-liquidity pool has its own implementation of CreatePoolMsg.

Note the PoolType type. This is an enumeration of all supported pool types. We proto-generate this enumeration:

// proto/osmosis/poolmanager/v1beta1/module_route.proto
// generates to x/poolmanager/types/module_route.pb.go

// PoolType is an enumeration of all supported pool types.
enum PoolType {
  option (gogoproto.goproto_enum_prefix) = false;

  // Balancer is the standard xy=k curve. Its pool model is defined in x/gamm.
  Balancer = 0;
  // Stableswap is the Solidly cfmm stable swap curve. Its pool model is defined
  // in x/gamm.
  StableSwap = 1;
  // Concentrated is the pool model specific to concentrated liquidity. It is
  // defined in x/concentrated-liquidity.
  Concentrated = 2;
}

Let's begin by considering the execution flow of the pool creation message. Assume balancer pool is being created.

  1. CreatePoolMsg is received by the x/gamm message server.

  2. CreatePool keeper method is called from poolmanager, propagating the appropriate implementation of the CreatePoolMsg interface.

// x/poolmanager/creator.go CreatePool(...)

// CreatePool attempts to create a pool returning the newly created pool ID or
// an error upon failure. The pool creation fee is used to fund the community
// pool. It will create a dedicated module account for the pool and sends the
// initial liquidity to the created module account.
//
// After the initial liquidity is sent to the pool's account, this function calls an
// InitializePool function from the source module. That module is responsible for:
// - saving the pool into its own state
// - Minting LP shares to pool creator
// - Setting metadata for the shares
func (k Keeper) CreatePool(ctx sdk.Context, msg types.CreatePoolMsg) (uint64, error) {
    ...
}

  1. The keeper utilizes CreatePoolMsg interface methods to execute the logic specific to each pool type.

  2. Lastly, poolmanager.CreatePool routes the execution to the appropriate module.

The propagation to the desired module is ensured by the routing table stored in memory in the poolmanager keeper.

// x/poolmanager/keeper.go NewKeeper(...)

func NewKeeper(...) *Keeper {
    ...

    routes := map[types.PoolType]types.SwapI{
        types.Balancer:     gammKeeper,
        types.Stableswap:   gammKeeper,
        types.Concentrated: concentratedKeeper,
    }

    return &Keeper{..., routes: routes}
}

MsgCreatePool interface defines the following method: GetPoolType() PoolType

As a result, poolmanagerkeeper.CreatePool can route the execution to the appropriate module in the following way:

// x/poolmanager/creator.go CreatePool(...)

swapModule := k.routes[msg.GetPoolType()]

if err := swapModule.InitializePool(ctx, pool, sender); err != nil {
    return 0, err
}

Where swapModule is either gamm or concentrated-liquidity keeper.

Both of these modules implement the SwapI interface:

// x/poolmanager/types/routes.go SwapI interface

type SwapI interface {
    ...

    InitializePool(ctx sdk.Context, pool gammtypes.PoolI, creatorAddress sdk.AccAddress) error
}

As a result, the poolmanager module propagates core execution to the appropriate swap module.

Lastly, the poolmanager keeper stores a mapping from the pool id to the pool type. This mapping is going to be necessary for knowing where to route the swap messages.

To achieve this, we create the following store index:

// x/poolmanager/types/keys.go

var (
    ...

    SwapModuleRouterPrefix     = []byte{0x02}
)

// N.B.: we proto-generate this struct. However, the proto
// definition is omitted for brevity.
type ModuleRoute struct {
    PoolType PoolType
}

// FormatModuleRouteKey serializes pool id with appropriate prefix into bytes.
func FormatModuleRouteKey(poolId uint64) []byte {
    return []byte(fmt.Sprintf("%s%d", SwapModuleRouterPrefix, poolId))
}

// ParseModuleRouteFromBz parses the raw bytes into ModuleRoute.
// Returns error if fails to parse or if the bytes are empty.
func ParseModuleRouteFromBz(bz []byte) (ModuleRoute, error) {
    // parsing logic
}

Swaps​

There are 4 swap messages:

  • MsgSwapExactAmountIn
  • MsgSwapExactAmountOut
  • MsgSplitRouteSwapExactAmountIn
  • MsgSplitRouteSwapExactAmountOut

Between, MsgSwapExactAmountIn and MsgSwapExactAmountOut, the implementation of routing is similar. We only focus on MsgSwapExactAmountIn below.

MsgSplitRouteSwapExactAmountIn and MsgSplitRouteSwapExactAmountOut support split routes where for each split route they call the respective MsgSwapExactAmountIn or MsgSwapExactAmountOut message. When using the split routes, the slippage protection is disabled on the per-route basis. For swap exact amount in, we provide zero for the min amount out. For swap exact amount out, we provide the max amount in which is 1 << 256 - 1. Read more about route splitting in the "Route Splitting" section.

Once the message is received, it calls RouteExactAmountIn

// x/poolmanager/router.go RouteExactAmountIn(...)

// RouteExactAmountIn defines the input denom and input amount for the first pool,
// the output of the first pool is chained as the input for the next routed pool
// transaction succeeds when final amount out is greater than tokenOutMinAmount defined.
func (k Keeper) RouteExactAmountIn(
    ctx sdk.Context,
    sender sdk.AccAddress,
    routes []types.SwapAmountInRoute,
    tokenIn sdk.Coin,
    tokenOutMinAmount sdk.Int) (tokenOutAmount sdk.Int, err error) {
}

Essentially, the method iterates over the routes and calls a SwapExactAmountIn method for each, subsequently updating the inter-pool swap state.

The routing works by querying the index SwapModuleRouterPrefix, searching up the poolmanagerkeeper.router mapping, and calling SwapExactAmountIn method of the appropriate module.

// x/poolmanager/router.go RouteExactAmountIn(...)

moduleRouteBytes := osmoutils.MustGet(poolmanagertypes.FormatModuleRouteIndex(poolId))
moduleRoute, _ := poolmanagertypes.ModuleRouteFromBytes(moduleRouteBytes)

swapModule := k.routes[moduleRoute.PoolType]

_ := swapModule.SwapExactAmountIn(...)
  • note that error checks and other details are omitted for brevity.

Similar to pool creation logic, we are able to call SwapExactAmountIn on any of the swap modules by implementing the SwapI interface:

// x/poolmanager/types/routes.go SwapI interface

type SwapI interface {
    ...

    SwapExactAmountIn(
        ctx sdk.Context,
        sender sdk.AccAddress,
        poolId gammtypes.PoolI,
        tokenIn sdk.Coin,
        tokenOutDenom string,
        tokenOutMinAmount sdk.Int,
        spreadFactor sdk.Dec,
    ) (sdk.Int, error)
}

During the process of swapping a specific asset, the token the user is putting into the pool is denoted as tokenIn, while the token that would be returned to the user, the asset that is being swapped for, after the swap is denoted as tokenOut throughout the module.

For example, in the context of balancer pools, given a tokenIn, the following calculations are done to calculate how many tokens are to be swapped into and removed from the pool:

tokenBalanceOut * [1 - { tokenBalanceIn / (tokenBalanceIn + (1 - spreadFactor) * tokenAmountIn)} ^ (tokenWeightIn / tokenWeightOut)]

The calculation is also able to be reversed, the case where user provides tokenOut. The calculation for the amount of tokens that the user should be putting in is done through the following formula:

tokenBalanceIn * [{tokenBalanceOut / (tokenBalanceOut - tokenAmountOut)} ^ (tokenWeightOut / tokenWeightIn) -1] / tokenAmountIn

Existing Swap types:

  • SwapExactAmountIn
  • SwapExactAmountOut

Messages​

MsgSwapExactAmountIn​

MsgSwapExactAmountIn

MsgSwapExactAmountOut​

MsgSwapExactAmountOut

MsgSplitRouteSwapExactAmountIn​

MsgSplitRouteSwapExactAmountIn

MsgSplitRouteSwapExactAmountOut​

MsgSplitRouteSwapExactAmountOut

Multi-Hop​

All tokens are swapped using a multi-hop mechanism. That is, all swaps are routed via the most cost-efficient way, swapping in and out from multiple pools in the process. The most cost-efficient route is determined offline and the list of the pools is provided externally, by user, during the broadcasting of the swapping transaction. At the moment of execution, the provided route may not be the most cost-efficient one anymore.

When a trade consists of just two OSMO-included routes during a single transaction, the spread factors on each hop would be automatically halved. Example: for converting ATOM -> OSMO -> LUNA using two pools with spread factors 0.3% + 0.2%, instead 0.15% + 0.1% spread factors will be applied.

Multi-Hop

Route Splitting​

Each route can be thought of as a separate multi-hop swap.

Splitting swaps across multiple pools for the same token pair can be beneficial for several reasons, primarily relating to reduced slippage, price impact, and potentially lower spreads.

Here's a detailed explanation of these advantages:

  • Reduced slippage: When a large trade is executed in a single pool, it can be significantly affected if someone else executes a large swap against that pool.

  • Lower price impact: When executing a large trade in a single pool, the price impact can be substantial, leading to a less favorable exchange rate for the trader. By splitting the swap across multiple pools, the price impact in each pool is minimized, resulting in a better overall exchange rate.

  • Improved liquidity utilization: Different pools may have varying levels of liquidity, spreads, and price curves. By splitting swaps across multiple pools, the router can utilize liquidity from various sources, allowing for more efficient execution of trades. This is particularly useful when the liquidity in a single pool is not sufficient to handle a large trade or when the price curve of one pool becomes less favorable as the trade size increases.

  • Potentially lower spreads: In some cases, splitting swaps across multiple pools may result in lower overall spreads. This can happen when different pools have different spread structures, or when the total spread paid across multiple pools is lower than the spread for executing the entire trade in a single pool with higher slippage.

Note, that the actual split happens off-chain. The router is only responsible for executing the swaps in the order and quantities of token in provided by the routes.