Make the yield estimation reject height that would invalidate the cac…

…he, fixes #147

x/starname/keeper/keeper.go

@@ -157,16 +157,14 @@ func (k Keeper) addOrRemoveFeesSum(ctx sdk.Context, height uint64, add bool) {
 }
 
 // GetBlockFeesSum retrieves the current value for the sum of the last n blocks
-func (k Keeper) GetBlockFeesSum(ctx sdk.Context, maxBlocksInSum uint64) (sdk.Coins, uint64) {
-	//FIXME: the block height is not updated when querying at a different height (only the stores are)
-	// So this line prevent to query from a different height (and will make the cms panic)
-	// Querying at previous heights also cause problems for the cached sliding sum
+func (k Keeper) GetBlockFeesSum(ctx sdk.Context, maxBlocksInSum uint64) (sdk.Coins, uint64, error) {
 	currentHeight := uint64(ctx.BlockHeight())
 
-	// Solves a bug where currentHeight is less than the last computed height, we always want to
-	// have the latest available data no matter what
+	// We force the query height to be greater than the latest computed height of the cached sliding sum otherwise querying
+	// at different height would cause high latency as the sum would have to be recomputed.
 	if currentHeight < slidingSum.lastComputedHeight {
-		currentHeight = slidingSum.lastComputedHeight
+		return nil, 0, fmt.Errorf("querying at past height is forbidden because of performance issues: queried " +
+			"height %v when last known height is %v", currentHeight, slidingSum.lastComputedHeight)
 	}
 
 	if currentHeight < maxBlocksInSum {
@@ -208,7 +206,7 @@ func (k Keeper) GetBlockFeesSum(ctx sdk.Context, maxBlocksInSum uint64) (sdk.Coi
 		}
 	}
 
-	return slidingSum.feesSum, slidingSum.feesSumCount
+	return slidingSum.feesSum, slidingSum.feesSumCount, nil
 }
 
 // GetBlockFees returns the fees collected at a specific height

x/starname/keeper/querier.go

@@ -332,8 +332,11 @@ func (q grpcQuerier) Yield(ctx context.Context, _ *types.QueryYieldRequest) (*ty
 
 func calculateYield(ctx sdk.Context, keeper *Keeper) (sdk.Dec, error) {
 
-	totalFees, numBlocks := keeper.GetBlockFeesSum(ctx, NumBlocksInAWeek)
+	totalFees, numBlocks, err := keeper.GetBlockFeesSum(ctx, NumBlocksInAWeek)
 
+	if err != nil {
+		return sdk.ZeroDec(), sdkerrors.Wrapf(err, "could not compute the fees for the latest blocks at height %v", ctx.BlockHeight())
+	}
 	if numBlocks != NumBlocksInAWeek {
 		return sdk.ZeroDec(), fmt.Errorf("not enough data to estimate yield: current height %v is smaller than %v",
 			ctx.BlockHeight(), NumBlocksInAWeek)