From 67d185ceb92f9c332d7338554d0d0d9788e09a39 Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Thu, 19 Jan 2017 19:45:52 +0100
Subject: [PATCH] Compact based on compaction generation

---
 block.go   | 16 ++++++++--------
 compact.go | 25 +++++++++++++++++++++----
 db.go      |  2 ++
 reader.go  |  5 ++++-
 4 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/block.go b/block.go
index 13e176718..8e9d0c2e7 100644
--- a/block.go
+++ b/block.go
@@ -46,6 +46,10 @@ type BlockMeta struct {
 		NumSeries  uint64 `json:"numSeries,omitempty"`
 		NumChunks  uint64 `json:"numChunks,omitempty"`
 	} `json:"stats,omitempty"`
+
+	Compaction struct {
+		Generation int `json:"generation"`
+	} `json:"compaction"`
 }
 
 const (
@@ -108,9 +112,11 @@ func writeMetaFile(dir string, meta *BlockMeta) error {
 }
 
 func newPersistedBlock(dir string) (*persistedBlock, error) {
-	// TODO(fabxc): validate match of name and stats time, validate magic.
+	meta, err := readMetaFile(dir)
+	if err != nil {
+		return nil, err
+	}
 
-	// mmap files belonging to the block.
 	chunksf, err := openMmapFile(chunksFileName(dir))
 	if err != nil {
 		return nil, errors.Wrap(err, "open chunk file")
@@ -129,11 +135,6 @@ func newPersistedBlock(dir string) (*persistedBlock, error) {
 		return nil, errors.Wrap(err, "create index reader")
 	}
 
-	meta, err := readMetaFile(dir)
-	if err != nil {
-		return nil, err
-	}
-
 	pb := &persistedBlock{
 		dir:     dir,
 		meta:    *meta,
@@ -142,7 +143,6 @@ func newPersistedBlock(dir string) (*persistedBlock, error) {
 		chunkr:  sr,
 		indexr:  ir,
 	}
-
 	return pb, nil
 }
 
diff --git a/compact.go b/compact.go
index 948cfb12d..9267dd5ef 100644
--- a/compact.go
+++ b/compact.go
@@ -64,29 +64,45 @@ func newCompactor(r prometheus.Registerer, opts *compactorOptions) *compactor {
 // pick returns a range [i, j] in the blocks that are suitable to be compacted
 // into a single block at position i.
 func (c *compactor) pick(bs []Block) (i, j int, ok bool) {
+
 	last := len(bs) - 1
 	if len(bs) == 0 {
 		return 0, 0, false
 	}
 
 	// Make sure we always compact the last block if unpersisted.
-	if !bs[last].Persisted() {
+	if bs[last].Meta().Compaction.Generation == 0 {
 		if len(bs) >= 3 && compactionMatch(bs[last-2:last+1]) {
 			return last - 2, last, true
 		}
 		return last, last, true
 	}
 
-	for i := 0; i+2 < len(bs); i += 3 {
-		tpl := bs[i : i+3]
+	for i := len(bs); i-3 >= 0; i -= 3 {
+		tpl := bs[i-3 : i]
 		if compactionMatch(tpl) {
-			return i, i + 2, true
+			return i - 3, i - 1, true
 		}
 	}
 	return 0, 0, false
 }
 
 func compactionMatch(blocks []Block) bool {
+	g := blocks[0].Meta().Compaction.Generation
+	if g >= 5 {
+		return false
+	}
+
+	for _, b := range blocks[1:] {
+		if b.Meta().Compaction.Generation == 0 {
+			continue
+		}
+		if b.Meta().Compaction.Generation != g {
+			return false
+		}
+	}
+	return true
+
 	// TODO(fabxc): check whether combined size is below maxCompactionSize.
 	// Apply maximum time range? or number of series? – might already be covered by size implicitly.
 
@@ -112,6 +128,7 @@ func compactionMatch(blocks []Block) bool {
 func mergeBlockMetas(blocks ...Block) (res BlockMeta) {
 	res.MinTime = blocks[0].Meta().MinTime
 	res.MaxTime = blocks[len(blocks)-1].Meta().MaxTime
+	res.Compaction.Generation = blocks[0].Meta().Compaction.Generation + 1
 
 	for _, b := range blocks {
 		res.Stats.NumSamples += b.Meta().Stats.NumSamples
diff --git a/db.go b/db.go
index 8cd1a51c4..99aa16810 100644
--- a/db.go
+++ b/db.go
@@ -222,6 +222,8 @@ func (db *DB) blocks() (bs []Block) {
 	return bs
 }
 
+// compact block in range [i, j] into a temporary directory and atomically
+// swap the blocks out on successful completion.
 func (db *DB) compact(i, j int) error {
 	if j < i {
 		return errors.New("invalid compaction block range")
diff --git a/reader.go b/reader.go
index e79d64337..a49fb794b 100644
--- a/reader.go
+++ b/reader.go
@@ -24,6 +24,9 @@ type seriesReader struct {
 }
 
 func newSeriesReader(b []byte) (*seriesReader, error) {
+	if len(b) < 4 {
+		return nil, errors.Wrap(errInvalidSize, "index header")
+	}
 	// Verify magic number.
 	if m := binary.BigEndian.Uint32(b[:4]); m != MagicSeries {
 		return nil, fmt.Errorf("invalid magic number %x", m)
@@ -91,7 +94,7 @@ var (
 )
 
 func newIndexReader(s SeriesReader, b []byte) (*indexReader, error) {
-	if len(b) < 16 {
+	if len(b) < 4 {
 		return nil, errors.Wrap(errInvalidSize, "index header")
 	}
 	r := &indexReader{