refactor: last cursor optimization function name (influxdata#21353)

Closes: influxdata#21330
bednar · May 13, 2021 · d89b9cb · d89b9cb
1 parent 4becb6d
commit d89b9cb
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Showing 3 changed files with 13 additions and 12 deletions.
diff --git a/storage/reads/aggregate_resultset.go b/storage/reads/aggregate_resultset.go
@@ -23,11 +23,12 @@ type windowAggregateResultSet struct {
 	err          error
 }
 
-// IsAscendingWindowAggregate checks two things: If the request passed in
+// IsLastDescendingAggregateOptimization checks two things: If the request passed in
 // is using the `last` aggregate type, and if it doesn't have a window. If both
 // conditions are met, it returns false, otherwise, it returns true.
-func IsAscendingWindowAggregate(req *datatypes.ReadWindowAggregateRequest) bool {
+func IsLastDescendingAggregateOptimization(req *datatypes.ReadWindowAggregateRequest) bool {
 	if len(req.Aggregate) != 1 {
+		// Descending optimization for last only applies when it is the only aggregate.
 		return false
 	}
 
@@ -38,13 +39,13 @@ func IsAscendingWindowAggregate(req *datatypes.ReadWindowAggregateRequest) bool
 	if req.Aggregate[0].Type == datatypes.AggregateTypeLast {
 		if req.Window == nil {
 			if req.WindowEvery == 0 || req.WindowEvery == math.MaxInt64 {
-				return false
+				return true
 			}
 		} else if (req.Window.Every.Nsecs == 0 && req.Window.Every.Months == 0) || req.Window.Every.Nsecs == math.MaxInt64 {
-			return false
+			return true
 		}
 	}
-	return true
+	return false
 }
 
 func NewWindowAggregateResultSet(ctx context.Context, req *datatypes.ReadWindowAggregateRequest, cursor SeriesCursor) (ResultSet, error) {
@@ -60,7 +61,7 @@ func NewWindowAggregateResultSet(ctx context.Context, req *datatypes.ReadWindowA
 		return nil, errors.Errorf(errors.InternalError, "attempt to create a windowAggregateResultSet with %v aggregate functions", nAggs)
 	}
 
-	ascending := IsAscendingWindowAggregate(req)
+	ascending := !IsLastDescendingAggregateOptimization(req)
 	results := &windowAggregateResultSet{
 		ctx:          ctx,
 		req:          req,

diff --git a/storage/reads/group_resultset.go b/storage/reads/group_resultset.go
@@ -40,11 +40,11 @@ func GroupOptionNilSortLo() GroupOption {
 	}
 }
 
-// IsAscendingGroupAggregate checks if this request is using the `last` aggregate type.
+// IsLastDescendingGroupOptimization checks if this request is using the `last` aggregate type.
 // It returns true if an ascending cursor should be used (all other conditions)
 // or a descending cursor (when `last` is used).
-func IsAscendingGroupAggregate(req *datatypes.ReadGroupRequest) bool {
-	return req.Aggregate == nil || req.Aggregate.Type != datatypes.AggregateTypeLast
+func IsLastDescendingGroupOptimization(req *datatypes.ReadGroupRequest) bool {
+	return req.Aggregate != nil && req.Aggregate.Type == datatypes.AggregateTypeLast
 }
 
 func NewGroupResultSet(ctx context.Context, req *datatypes.ReadGroupRequest, newSeriesCursorFn func() (SeriesCursor, error), opts ...GroupOption) GroupResultSet {
@@ -61,7 +61,7 @@ func NewGroupResultSet(ctx context.Context, req *datatypes.ReadGroupRequest, new
 		o(g)
 	}
 
-	ascending := IsAscendingGroupAggregate(req)
+	ascending := !IsLastDescendingGroupOptimization(req)
 	g.arrayCursors = newMultiShardArrayCursors(ctx, req.Range.Start, req.Range.End, ascending)
 
 	for i, k := range req.GroupKeys {

diff --git a/v1/services/storage/store.go b/v1/services/storage/store.go
@@ -74,7 +74,7 @@ func (s *Store) WindowAggregate(ctx context.Context, req *datatypes.ReadWindowAg
 	// Due to some optimizations around how flux's `last()` function is implemented with the
 	// storage engine, we need to detect if the read request requires a descending
 	// cursor or not.
-	descending := !reads.IsAscendingWindowAggregate(req)
+	descending := reads.IsLastDescendingAggregateOptimization(req)
 	shardIDs, err := s.findShardIDs(database, rp, descending, start, end)
 	if err != nil {
 		return nil, err
@@ -212,7 +212,7 @@ func (s *Store) ReadGroup(ctx context.Context, req *datatypes.ReadGroupRequest)
 	// Due to some optimizations around how flux's `last()` function is implemented with the
 	// storage engine, we need to detect if the read request requires a descending
 	// cursor or not.
-	descending := !reads.IsAscendingGroupAggregate(req)
+	descending := reads.IsLastDescendingGroupOptimization(req)
 	shardIDs, err := s.findShardIDs(database, rp, descending, start, end)
 	if err != nil {
 		return nil, err