fix: better fix integer overrun when calculating parallelism for very long time range queries (#17430)

Author: slim-bean

pkg/querier/queryrange/limits.go

@@ -679,7 +679,11 @@ func WeightedParallelism(
 		}
 	}
 
-	totalDur := int64(tsdbDur + otherDur)
+	// We don't need nanosecond precision here so convert to seconds.
+	// This is also important to prevent overflowing int64 when multiplying by parallelism below.
+	tsdbDur = tsdbDur / 1e9
+	otherDur = otherDur / 1e9
+	totalDur := int(tsdbDur + otherDur)
 	// If totalDur is 0, the query likely does not overlap any of the schema configs so just use parallelism of 1 and
 	// let the downstream code handle it.
 	if totalDur == 0 {
@@ -688,8 +692,8 @@ func WeightedParallelism(
 		return 1
 	}
 
-	tsdbPart := int64(tsdbDur) * int64(tsdbMaxQueryParallelism) / totalDur
-	regPart := int64(otherDur) * int64(regMaxQueryParallelism) / totalDur
+	tsdbPart := int(tsdbDur) * tsdbMaxQueryParallelism / totalDur
+	regPart := int(otherDur) * regMaxQueryParallelism / totalDur
 
 	if combined := regPart + tsdbPart; combined > 0 {
 		return int(combined)

pkg/querier/queryrange/limits_test.go

@@ -667,7 +667,7 @@ func Test_GenerateCacheKey_NoDivideZero(t *testing.T) {
 
 func Test_WeightedParallelism(t *testing.T) {
 	limits := &fakeLimits{
-		tsdbMaxQueryParallelism: 100,
+		tsdbMaxQueryParallelism: 2048,
 		maxQueryParallelism:     10,
 	}
 
@@ -727,25 +727,25 @@ func Test_WeightedParallelism(t *testing.T) {
 				desc:  "50% each",
 				start: borderTime.Add(-time.Hour),
 				end:   borderTime.Add(time.Hour),
-				exp:   55,
+				exp:   1029,
 			},
 			{
 				desc:  "75/25 split",
 				start: borderTime.Add(-3 * time.Hour),
 				end:   borderTime.Add(time.Hour),
-				exp:   32,
+				exp:   519,
 			},
 			{
 				desc:  "start==end",
 				start: borderTime.Add(time.Hour),
 				end:   borderTime.Add(time.Hour),
-				exp:   100,
+				exp:   2048,
 			},
 			{
-				desc:  "huge range which previously overflowed int",
-				start: model.Now().Add(-24 * 60 * time.Hour),
-				end:   model.Now(),
-				exp:   100,
+				desc:  "huge range to make sure we don't int overflow in the calculations.",
+				start: borderTime,
+				end:   borderTime.Add(24 * time.Hour * 365 * 20),
+				exp:   2048,
 			},
 		} {
 			t.Run(cfgs.desc+tc.desc, func(t *testing.T) {