remote_write: round desired shards up before check

Previously we would reject an increase from 2 to 2.5 as being
within 30%; by rounding up first we see this as an increase from 2 to 3.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

storage/remote/queue_manager.go

@@ -859,11 +859,13 @@ func (t *QueueManager) calculateDesiredShards() int {
 	)
 	level.Debug(t.logger).Log("msg", "QueueManager.updateShardsLoop",
 		"lowerBound", lowerBound, "desiredShards", desiredShards, "upperBound", upperBound)
+
+	desiredShards = math.Ceil(desiredShards) // Round up to be on the safe side.
 	if lowerBound <= desiredShards && desiredShards <= upperBound {
 		return t.numShards
 	}
 
-	numShards := int(math.Ceil(desiredShards))
+	numShards := int(desiredShards)
 	// Do not downshard if we are more than ten seconds back.
 	if numShards < t.numShards && delay > 10.0 {
 		level.Debug(t.logger).Log("msg", "Not downsharding due to being too far behind")

storage/remote/queue_manager_test.go

@@ -1025,7 +1025,7 @@ func TestCalculateDesiredShardsDetail(t *testing.T) {
 			dataIn:          10,
 			dataOut:         10,
 			dataOutDuration: 1.2,
-			expectedShards:  1, // no reaction - less than 30% change
+			expectedShards:  2, // 1.2 is rounded up to 2.
 		},
 		{
 			name:            "bigger slowdown",
@@ -1033,7 +1033,7 @@ func TestCalculateDesiredShardsDetail(t *testing.T) {
 			dataIn:          10,
 			dataOut:         10,
 			dataOutDuration: 1.4,
-			expectedShards:  2, // now it shards up
+			expectedShards:  2,
 		},
 		{
 			name:            "speed up",