Make interval overlap comparisons more explicit

Blocks are half-open intervals [a, b), while all other intervals
(chunks, head, ...) are closed intervals [a, b].

Make that distinction explicit by defining `OverlapsClosedInterval()`
methods for blocks and chunks, and using them in place of the more
generic `intervalOverlap()` function.

This change also fixes `db.Querier()` and `db.Delete()`, which could
previously return one extraneous block at the end of the specified
interval.

Signed-off-by: Benoît Knecht <benoit.knecht@fsfe.org>

block.go

@@ -447,7 +447,7 @@ Outer:
 		}
 
 		for _, chk := range chks {
-			if intervalOverlap(mint, maxt, chk.MinTime, chk.MaxTime) {
+			if chk.OverlapsClosedInterval(mint, maxt) {
 				// Delete only until the current values and not beyond.
 				tmin, tmax := clampInterval(mint, maxt, chks[0].MinTime, chks[len(chks)-1].MaxTime)
 				stones[p.At()] = Intervals{{tmin, tmax}}
@@ -539,6 +539,13 @@ func (pb *Block) Snapshot(dir string) error {
 	return nil
 }
 
+// Returns true if the block overlaps [mint, maxt].
+func (pb *Block) OverlapsClosedInterval(mint, maxt int64) bool {
+	// The block itself is a half-open interval
+	// [pb.meta.MinTime, pb.meta.MaxTime).
+	return pb.meta.MinTime <= maxt && mint < pb.meta.MaxTime
+}
+
 func clampInterval(a, b, mint, maxt int64) (int64, int64) {
 	if a < mint {
 		a = mint

chunks/chunks.go

@@ -57,6 +57,12 @@ func (cm *Meta) writeHash(h hash.Hash) error {
 	return nil
 }
 
+// Returns true if the chunk overlaps [mint, maxt].
+func (cm *Meta) OverlapsClosedInterval(mint, maxt int64) bool {
+	// The chunk itself is a closed interval [cm.MinTime, cm.MaxTime].
+	return cm.MinTime <= maxt && mint <= cm.MaxTime
+}
+
 var (
 	errInvalidSize     = fmt.Errorf("invalid size")
 	errInvalidFlag     = fmt.Errorf("invalid flag")

compact.go

@@ -592,7 +592,7 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 		if len(dranges) > 0 {
 			// Re-encode the chunk to not have deleted values.
 			for i, chk := range chks {
-				if !intervalOverlap(dranges[0].Mint, dranges[len(dranges)-1].Maxt, chk.MinTime, chk.MaxTime) {
+				if !chk.OverlapsClosedInterval(dranges[0].Mint, dranges[len(dranges)-1].Maxt) {
 					continue
 				}
 

db.go

@@ -762,8 +762,7 @@ func (db *DB) Querier(mint, maxt int64) (Querier, error) {
 	defer db.mtx.RUnlock()
 
 	for _, b := range db.blocks {
-		m := b.Meta()
-		if intervalOverlap(mint, maxt, m.MinTime, m.MaxTime) {
+		if b.OverlapsClosedInterval(mint, maxt) {
 			blocks = append(blocks, b)
 		}
 	}
@@ -805,8 +804,7 @@ func (db *DB) Delete(mint, maxt int64, ms ...labels.Matcher) error {
 	defer db.mtx.RUnlock()
 
 	for _, b := range db.blocks {
-		m := b.Meta()
-		if intervalOverlap(mint, maxt, m.MinTime, m.MaxTime) {
+		if b.OverlapsClosedInterval(mint, maxt) {
 			g.Go(func(b *Block) func() error {
 				return func() error { return b.Delete(mint, maxt, ms...) }
 			}(b))
@@ -854,11 +852,6 @@ func (db *DB) CleanTombstones() (err error) {
 	return errors.Wrap(db.reload(), "reload blocks")
 }
 
-func intervalOverlap(amin, amax, bmin, bmax int64) bool {
-	// Checks Overlap: http://stackoverflow.com/questions/3269434/
-	return amin <= bmax && bmin <= amax
-}
-
 func isBlockDir(fi os.FileInfo) bool {
 	if !fi.IsDir() {
 		return false

head.go

@@ -735,19 +735,14 @@ func (h *headChunkReader) Chunk(ref uint64) (chunkenc.Chunk, error) {
 	s.Lock()
 	c := s.chunk(int(cid))
 
-	// This means that the chunk has been garbage collected.
-	if c == nil {
+	// This means that the chunk has been garbage collected or is outside
+	// the specified range.
+	if c == nil || !c.OverlapsClosedInterval(h.mint, h.maxt) {
 		s.Unlock()
 		return nil, ErrNotFound
 	}
-
-	mint, maxt := c.minTime, c.maxTime
 	s.Unlock()
 
-	// Do not expose chunks that are outside of the specified range.
-	if c == nil || !intervalOverlap(mint, maxt, h.mint, h.maxt) {
-		return nil, ErrNotFound
-	}
 	return &safeChunk{
 		Chunk: c.chunk,
 		s:     s,
@@ -852,7 +847,7 @@ func (h *headIndexReader) Series(ref uint64, lbls *labels.Labels, chks *[]chunks
 
 	for i, c := range s.chunks {
 		// Do not expose chunks that are outside of the specified range.
-		if !intervalOverlap(c.minTime, c.maxTime, h.mint, h.maxt) {
+		if !c.OverlapsClosedInterval(h.mint, h.maxt) {
 			continue
 		}
 		*chks = append(*chks, chunks.Meta{
@@ -1291,6 +1286,11 @@ type memChunk struct {
 	minTime, maxTime int64
 }
 
+// Returns true if the chunk overlaps [mint, maxt].
+func (mc *memChunk) OverlapsClosedInterval(mint, maxt int64) bool {
+	return mc.minTime <= maxt && mint <= mc.maxTime
+}
+
 type memSafeIterator struct {
 	chunkenc.Iterator