chore: Remove unnecessary errors from splitter. (#16109)

**What this PR does / why we need it**:
Originally the splitter middleware had to parse the query and thus could return an error. However, parsing is done earlier now so no error is returned.

pkg/querier/queryrange/limits.go

@@ -48,9 +48,7 @@ const (
 	limErrQuerierTooManyBytesShardableTmpl   = "shard query is too large to execute on a single querier: (query: %s, limit: %s); consider adding more specific stream selectors or reduce the time range of the query"
 )
 
-var (
-	ErrMaxQueryParalellism = fmt.Errorf("querying is disabled, please contact your Loki operator")
-)
+var ErrMaxQueryParalellism = fmt.Errorf("querying is disabled, please contact your Loki operator")
 
 type Limits queryrange_limits.Limits
 
@@ -480,9 +478,7 @@ func (s *SemaphoreWithTiming) Acquire(ctx context.Context, n int64) (time.Durati
 }
 
 func (rt limitedRoundTripper) Do(c context.Context, request queryrangebase.Request) (queryrangebase.Response, error) {
-	var (
-		ctx, cancel = context.WithCancel(c)
-	)
+	ctx, cancel := context.WithCancel(c)
 	defer func() {
 		cancel()
 	}()
@@ -523,7 +519,6 @@ func (rt limitedRoundTripper) Do(c context.Context, request queryrangebase.Reque
 			// Note: It is the responsibility of the caller to run
 			// the handler in parallel.
 			elapsed, err := semWithTiming.Acquire(ctx, int64(1))
-
 			if err != nil {
 				return nil, fmt.Errorf("could not acquire work: %w", err)
 			}

pkg/querier/queryrange/querysharding.go

@@ -162,11 +162,7 @@ func (ast *astMapperware) Do(ctx context.Context, r queryrangebase.Request) (que
 		return nil, err
 	}
 
-	maxRVDuration, maxOffset, err := maxRangeVectorAndOffsetDuration(params.GetExpression())
-	if err != nil {
-		level.Warn(spLogger).Log("err", err.Error(), "msg", "failed to get range-vector and offset duration so skipped AST mapper for request")
-		return ast.next.Do(ctx, r)
-	}
+	maxRVDuration, maxOffset := maxRangeVectorAndOffsetDuration(params.GetExpression())
 
 	conf, err := ast.confs.GetConf(int64(model.Time(r.GetStart().UnixMilli()).Add(-maxRVDuration).Add(-maxOffset)), int64(model.Time(r.GetEnd().UnixMilli()).Add(-maxOffset)))
 	// cannot shard with this timerange

pkg/querier/queryrange/split_by_interval.go

@@ -195,10 +195,7 @@ func (h *splitByInterval) Do(ctx context.Context, r queryrangebase.Request) (que
 		return h.next.Do(ctx, r)
 	}
 
-	intervals, err := h.splitter.split(time.Now().UTC(), tenantIDs, r, interval)
-	if err != nil {
-		return nil, err
-	}
+	intervals := h.splitter.split(time.Now().UTC(), tenantIDs, r, interval)
 
 	h.metrics.splits.Observe(float64(len(intervals)))
 
@@ -260,13 +257,14 @@ func maxRangeVectorAndOffsetDurationFromQueryString(q string) (time.Duration, ti
 	if err != nil {
 		return 0, 0, err
 	}
-	return maxRangeVectorAndOffsetDuration(parsed)
+	dur, offset := maxRangeVectorAndOffsetDuration(parsed)
+	return dur, offset, nil
 }
 
 // maxRangeVectorAndOffsetDuration returns the maximum range vector and offset duration within a LogQL query.
-func maxRangeVectorAndOffsetDuration(expr syntax.Expr) (time.Duration, time.Duration, error) {
+func maxRangeVectorAndOffsetDuration(expr syntax.Expr) (time.Duration, time.Duration) {
 	if _, ok := expr.(syntax.SampleExpr); !ok {
-		return 0, 0, nil
+		return 0, 0
 	}
 
 	var maxRVDuration, maxOffset time.Duration
@@ -280,5 +278,5 @@ func maxRangeVectorAndOffsetDuration(expr syntax.Expr) (time.Duration, time.Dura
 			}
 		}
 	})
-	return maxRVDuration, maxOffset, nil
+	return maxRVDuration, maxOffset
 }

pkg/querier/queryrange/split_by_interval_test.go

@@ -500,8 +500,7 @@ func Test_splitQuery(t *testing.T) {
 						intervals.splitter = newDefaultSplitter(fakeLimits{}, nil)
 					}
 
-					splits, err := intervals.splitter.split(refTime, []string{tenantID}, req, intervals.splitInterval)
-					require.NoError(t, err)
+					splits := intervals.splitter.split(refTime, []string{tenantID}, req, intervals.splitInterval)
 					assertSplits(t, want, splits)
 				})
 			}
@@ -738,8 +737,7 @@ func Test_splitRecentMetadataQuery(t *testing.T) {
 						intervals.splitter = newDefaultSplitter(fakeLimits{}, nil)
 					}
 
-					splits, err := intervals.splitter.split(refTime, []string{tenantID}, req, intervals.splitInterval)
-					require.NoError(t, err)
+					splits := intervals.splitter.split(refTime, []string{tenantID}, req, intervals.splitInterval)
 					assertSplits(t, want, splits)
 				})
 			}
@@ -1136,7 +1134,7 @@ func Test_splitMetricQuery(t *testing.T) {
 			},
 			expected: []queryrangebase.Request{
 				&LokiRequest{
-					StartTs: time.Date(2023, 1, 15, 7, 05, 30, 0, time.UTC), // start time is aligned down to step of 15s
+					StartTs: time.Date(2023, 1, 15, 7, 0o5, 30, 0, time.UTC), // start time is aligned down to step of 15s
 					EndTs:   time.Date(2023, 1, 15, 7, 29, 45, 0, time.UTC),
 					Step:    15 * seconds,
 					Query:   shortRange,
@@ -1349,8 +1347,7 @@ func Test_splitMetricQuery(t *testing.T) {
 				ms = tc.splitter.(*metricQuerySplitter)
 			}
 
-			splits, err := ms.split(refTime, []string{tenantID}, tc.input, tc.splitInterval)
-			require.NoError(t, err)
+			splits := ms.split(refTime, []string{tenantID}, tc.input, tc.splitInterval)
 			if !assert.Equal(t, tc.expected, splits) {
 				t.Logf("expected and actual do not match\n")
 				defer t.Fail()
@@ -1660,7 +1657,8 @@ func Test_seriesvolume_splitByInterval_Do(t *testing.T) {
 						{Name: `{foo="bar"}`, Volume: 38},
 						{Name: `{bar="baz"}`, Volume: 28},
 					},
-					Limit: 2},
+					Limit: 2,
+				},
 				Headers: nil,
 			}, nil
 		})
@@ -1700,7 +1698,8 @@ func Test_seriesvolume_splitByInterval_Do(t *testing.T) {
 						{Name: `{foo="bar"}`, Volume: 38},
 						{Name: `{fizz="buzz"}`, Volume: 28},
 					},
-					Limit: 1},
+					Limit: 1,
+				},
 				Headers: nil,
 			}, nil
 		})
@@ -1740,7 +1739,8 @@ func Test_seriesvolume_splitByInterval_Do(t *testing.T) {
 						{Name: `{foo="bar"}`, Volume: 38},
 						{Name: `{bar="baz"}`, Volume: 28},
 					},
-					Limit: 2},
+					Limit: 2,
+				},
 				Headers: nil,
 			}, nil
 		})

pkg/querier/queryrange/splitters.go

@@ -16,7 +16,7 @@ import (
 )
 
 type splitter interface {
-	split(execTime time.Time, tenantIDs []string, request queryrangebase.Request, interval time.Duration) ([]queryrangebase.Request, error)
+	split(execTime time.Time, tenantIDs []string, request queryrangebase.Request, interval time.Duration) []queryrangebase.Request
 }
 
 type defaultSplitter struct {
@@ -28,7 +28,7 @@ func newDefaultSplitter(limits Limits, iqo util.IngesterQueryOptions) *defaultSp
 	return &defaultSplitter{limits, iqo}
 }
 
-func (s *defaultSplitter) split(execTime time.Time, tenantIDs []string, req queryrangebase.Request, interval time.Duration) ([]queryrangebase.Request, error) {
+func (s *defaultSplitter) split(execTime time.Time, tenantIDs []string, req queryrangebase.Request, interval time.Duration) []queryrangebase.Request {
 	var (
 		reqs             []queryrangebase.Request
 		factory          func(start, end time.Time)
@@ -126,7 +126,7 @@ func (s *defaultSplitter) split(execTime time.Time, tenantIDs []string, req quer
 		}
 	default:
 		level.Warn(util_log.Logger).Log("msg", fmt.Sprintf("splitter: unsupported request type: %T", req))
-		return nil, nil
+		return nil
 	}
 
 	var (
@@ -175,7 +175,7 @@ func (s *defaultSplitter) split(execTime time.Time, tenantIDs []string, req quer
 
 		// query only overlaps ingester query window or recent metadata query window, nothing more to do
 		if start.After(end) || start.Equal(end) {
-			return reqs, nil
+			return reqs
 		}
 
 		// copy the splits, reset the results
@@ -191,7 +191,7 @@ func (s *defaultSplitter) split(execTime time.Time, tenantIDs []string, req quer
 
 	// move the ingester or recent metadata splits to the end to maintain correct order
 	reqs = append(reqs, splitsBeforeRebound...)
-	return reqs, nil
+	return reqs
 }
 
 type metricQuerySplitter struct {
@@ -205,15 +205,12 @@ func newMetricQuerySplitter(limits Limits, iqo util.IngesterQueryOptions) *metri
 
 // reduceSplitIntervalForRangeVector reduces the split interval for a range query based on the duration of the range vector.
 // Large range vector durations will not be split into smaller intervals because it can cause the queries to be slow by over-processing data.
-func (s *metricQuerySplitter) reduceSplitIntervalForRangeVector(r *LokiRequest, interval time.Duration) (time.Duration, error) {
-	maxRange, _, err := maxRangeVectorAndOffsetDuration(r.Plan.AST)
-	if err != nil {
-		return 0, err
-	}
+func (s *metricQuerySplitter) reduceSplitIntervalForRangeVector(r *LokiRequest, interval time.Duration) time.Duration {
+	maxRange, _ := maxRangeVectorAndOffsetDuration(r.Plan.AST)
 	if maxRange > interval {
-		return maxRange, nil
+		return maxRange
 	}
-	return interval, nil
+	return interval
 }
 
 // Round up to the step before the next interval boundary.
@@ -229,15 +226,12 @@ func (s *metricQuerySplitter) nextIntervalBoundary(t time.Time, step int64, inte
 	return time.Unix(0, target)
 }
 
-func (s *metricQuerySplitter) split(execTime time.Time, tenantIDs []string, r queryrangebase.Request, interval time.Duration) ([]queryrangebase.Request, error) {
+func (s *metricQuerySplitter) split(execTime time.Time, tenantIDs []string, r queryrangebase.Request, interval time.Duration) []queryrangebase.Request {
 	var reqs []queryrangebase.Request
 
 	lokiReq := r.(*LokiRequest)
 
-	interval, err := s.reduceSplitIntervalForRangeVector(lokiReq, interval)
-	if err != nil {
-		return nil, err
-	}
+	interval = s.reduceSplitIntervalForRangeVector(lokiReq, interval)
 
 	start, end := s.alignStartEnd(r.GetStep(), lokiReq.StartTs, lokiReq.EndTs)
 
@@ -262,7 +256,7 @@ func (s *metricQuerySplitter) split(execTime time.Time, tenantIDs []string, r qu
 	if lokiReq.Step >= interval.Milliseconds() {
 		util.ForInterval(time.Duration(lokiReq.Step*1e6), lokiReq.StartTs, lokiReq.EndTs, false, factory)
 
-		return reqs, nil
+		return reqs
 	}
 
 	var (
@@ -291,7 +285,7 @@ func (s *metricQuerySplitter) split(execTime time.Time, tenantIDs []string, r qu
 
 		// query only overlaps ingester query window, nothing more to do
 		if start.After(end) || start.Equal(end) {
-			return reqs, nil
+			return reqs
 		}
 
 		// copy the splits, reset the results
@@ -308,7 +302,7 @@ func (s *metricQuerySplitter) split(execTime time.Time, tenantIDs []string, r qu
 	// move the ingester splits to the end to maintain correct order
 	reqs = append(reqs, ingesterSplits...)
 
-	return reqs, nil
+	return reqs
 }
 
 func (s *metricQuerySplitter) alignStartEnd(step int64, start, end time.Time) (time.Time, time.Time) {