x/incentives: get to distribute coins with single iteration

[czarcas7ic]

Background

getToDistributeCoinsFromGauges currently requires multiple iterations over all gauges

osmosis/x/incentives/keeper/distribute.go

Lines 24 to 31 in fb0de8c

	// getToDistributeCoinsFromGauges returns coins that have not been distributed yet from the provided gauges
	func (k Keeper) getToDistributeCoinsFromGauges(gauges []types.Gauge) sdk.Coins {
	// TODO: Consider optimizing this in the future to only require one iteration over all gauges.
	// TODO: Lets make issue for this, requires changing getGaugesFromIterator logic in gauge.go
	coins := k.getCoinsFromGauges(gauges)
	distributed := k.getDistributedCoinsFromGauges(gauges)
	return coins.Sub(distributed)
	}

Suggested Design

I believe this would require making changes to the getGaugesFromIterator logic in gauge.go found here

osmosis/x/incentives/keeper/gauge.go

Lines 19 to 38 in fb0de8c

	// getGaugesFromIterator iterates over everything in a gauge's iterator, until it reaches the end. Return all gauges iterated over.
	func (k Keeper) getGaugesFromIterator(ctx sdk.Context, iterator db.Iterator) []types.Gauge {
	gauges := []types.Gauge{}
	defer iterator.Close()
	for ; iterator.Valid(); iterator.Next() {
	gaugeIDs := []uint64{}
	err := json.Unmarshal(iterator.Value(), &gaugeIDs)
	if err != nil {
	panic(err)
	}
	for _, gaugeID := range gaugeIDs {
	gauge, err := k.GetGaugeByID(ctx, gaugeID)
	if err != nil {
	panic(err)
	}
	gauges = append(gauges, *gauge)
	}
	}
	return gauges
	}

Acceptance Criteria

• Getting toDistribute coins should only require one iteration over all gauges
• All existing tests should pass