From 2581648f70912f6af93a162b543e76749ce29b4a Mon Sep 17 00:00:00 2001
From: beorn7 <beorn@soundcloud.com>
Date: Wed, 2 Mar 2016 13:45:17 +0100
Subject: [PATCH] Separate iterators by offset

Add test that exposes the problem.
---
 promql/analyzer.go         | 12 +++++++-----
 storage/local/chunk.go     |  6 +++---
 storage/local/interface.go |  2 +-
 storage/local/preload.go   |  2 +-
 4 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/promql/analyzer.go b/promql/analyzer.go
index 3bc46bb8f..6e052656d 100644
--- a/promql/analyzer.go
+++ b/promql/analyzer.go
@@ -125,8 +125,10 @@ func (a *Analyzer) Prepare(ctx context.Context) (local.Preloader, error) {
 	}()
 
 	// Preload all analyzed ranges.
-	iters := map[model.Fingerprint]local.SeriesIterator{}
+	iters := map[time.Duration]map[model.Fingerprint]local.SeriesIterator{}
 	for offset, pt := range a.offsetPreloadTimes {
+		itersForDuration := map[model.Fingerprint]local.SeriesIterator{}
+		iters[offset] = itersForDuration
 		start := a.Start.Add(-offset)
 		end := a.End.Add(-offset)
 		for fp, rangeDuration := range pt.ranges {
@@ -148,7 +150,7 @@ func (a *Analyzer) Prepare(ctx context.Context) (local.Preloader, error) {
 			if err != nil {
 				return nil, err
 			}
-			iters[fp] = iter
+			itersForDuration[fp] = iter
 		}
 		for fp := range pt.instants {
 			if err = contextDone(ctx, env); err != nil {
@@ -161,7 +163,7 @@ func (a *Analyzer) Prepare(ctx context.Context) (local.Preloader, error) {
 			if err != nil {
 				return nil, err
 			}
-			iters[fp] = iter
+			itersForDuration[fp] = iter
 		}
 	}
 
@@ -170,11 +172,11 @@ func (a *Analyzer) Prepare(ctx context.Context) (local.Preloader, error) {
 		switch n := node.(type) {
 		case *VectorSelector:
 			for fp := range n.metrics {
-				n.iterators[fp] = iters[fp]
+				n.iterators[fp] = iters[n.Offset][fp]
 			}
 		case *MatrixSelector:
 			for fp := range n.metrics {
-				n.iterators[fp] = iters[fp]
+				n.iterators[fp] = iters[n.Offset][fp]
 			}
 		}
 		return true
diff --git a/storage/local/chunk.go b/storage/local/chunk.go
index ac54a5dc1..e0be10b14 100644
--- a/storage/local/chunk.go
+++ b/storage/local/chunk.go
@@ -54,7 +54,7 @@ const (
 )
 
 // chunkDesc contains meta-data for a chunk. Pay special attention to the
-// documented requirements for calling its method concurrently (WRT pinning and
+// documented requirements for calling its methods concurrently (WRT pinning and
 // locking). The doc comments spell out the requirements for each method, but
 // here is an overview and general explanation:
 //
@@ -71,7 +71,7 @@ const (
 // or creation) or by locking the fingerprint of the series the chunkDesc
 // belongs to. The affected methods are: add, maybePopulateLastTime, setChunk.
 //
-// Finally, there is the special cases firstTime and lastTime. lastTime requires
+// Finally, there are the special cases firstTime and lastTime. lastTime requires
 // to have locked the fingerprint of the series but the chunk does not need to
 // be pinned. That's because the chunkLastTime field in chunkDesc gets populated
 // upon completion of the chunk (when it is still pinned, and which happens
@@ -292,7 +292,7 @@ type chunkIterator interface {
 	// Gets the last sample value in the chunk.
 	lastSampleValue() model.SampleValue
 	// Gets the value that is closest before the given time. In case a value
-	// exist at precisely the given time, that value is returned. If no
+	// exists at precisely the given time, that value is returned. If no
 	// applicable value exists, a SamplePair with timestamp model.Earliest
 	// and value 0.0 is returned.
 	valueAtOrBeforeTime(model.Time) model.SamplePair
diff --git a/storage/local/interface.go b/storage/local/interface.go
index a62a13b19..005b39726 100644
--- a/storage/local/interface.go
+++ b/storage/local/interface.go
@@ -72,7 +72,7 @@ type Storage interface {
 // of the series prior the modification.
 type SeriesIterator interface {
 	// Gets the value that is closest before the given time. In case a value
-	// exist at precisely the given time, that value is returned. If no
+	// exists at precisely the given time, that value is returned. If no
 	// applicable value exists, a SamplePair with timestamp model.Earliest
 	// and value 0.0 is returned.
 	ValueAtOrBeforeTime(model.Time) model.SamplePair
diff --git a/storage/local/preload.go b/storage/local/preload.go
index cda04a864..08a88875f 100644
--- a/storage/local/preload.go
+++ b/storage/local/preload.go
@@ -28,7 +28,7 @@ func (p *memorySeriesPreloader) PreloadRange(
 ) (SeriesIterator, error) {
 	cds, iter, err := p.storage.preloadChunksForRange(fp, from, through)
 	if err != nil {
-		return iter, err
+		return nil, err
 	}
 	p.pinnedChunkDescs = append(p.pinnedChunkDescs, cds...)
 	return iter, nil