Add list of source head blocks to meta.json

block.go

@@ -85,17 +85,27 @@ type BlockMeta struct {
 	MaxTime int64 `json:"maxTime"`
 
 	// Stats about the contents of the block.
-	Stats struct {
-		NumSamples    uint64 `json:"numSamples,omitempty"`
-		NumSeries     uint64 `json:"numSeries,omitempty"`
-		NumChunks     uint64 `json:"numChunks,omitempty"`
-		NumTombstones uint64 `json:"numTombstones,omitempty"`
-	} `json:"stats,omitempty"`
+	Stats BlockStats `json:"stats,omitempty"`
 
 	// Information on compactions the block was created from.
-	Compaction struct {
-		Generation int `json:"generation"`
-	} `json:"compaction"`
+	Compaction BlockMetaCompaction `json:"compaction"`
+}
+
+// BlockStats contains stats about contents of a block.
+type BlockStats struct {
+	NumSamples    uint64 `json:"numSamples,omitempty"`
+	NumSeries     uint64 `json:"numSeries,omitempty"`
+	NumChunks     uint64 `json:"numChunks,omitempty"`
+	NumTombstones uint64 `json:"numTombstones,omitempty"`
+}
+
+// BlockMetaCompaction holds information about compactions a block went through.
+type BlockMetaCompaction struct {
+	// Maximum number of compaction cycles any source block has
+	// gone through.
+	Generation int `json:"generation"`
+	// ULIDs of all source head blocks that went into the block.
+	Sources []ulid.ULID `json:"sources,omitempty"`
 }
 
 const (
@@ -144,7 +154,7 @@ func writeMetaFile(dir string, meta *BlockMeta) error {
 	var merr MultiError
 	if merr.Add(enc.Encode(&blockMeta{Version: 1, BlockMeta: meta})); merr.Err() != nil {
 		merr.Add(f.Close())
-		return merr
+		return merr.Err()
 	}
 	if err := f.Close(); err != nil {
 		return err

compact.go

@@ -166,17 +166,35 @@ func (c *compactor) match(dirs []dirMeta) bool {
 	return uint64(dirs[len(dirs)-1].meta.MaxTime-dirs[0].meta.MinTime) <= c.opts.maxBlockRange
 }
 
-func mergeBlockMetas(blocks ...Block) (res BlockMeta) {
-	m0 := blocks[0].Meta()
+func compactBlockMetas(blocks ...BlockMeta) (res BlockMeta) {
+	res.MinTime = blocks[0].MinTime
+	res.MaxTime = blocks[len(blocks)-1].MaxTime
 
-	res.MinTime = m0.MinTime
-	res.MaxTime = blocks[len(blocks)-1].Meta().MaxTime
-
-	res.Compaction.Generation = m0.Compaction.Generation + 1
+	sources := map[ulid.ULID]struct{}{}
 
 	for _, b := range blocks {
-		res.Stats.NumSamples += b.Meta().Stats.NumSamples
+		res.Stats.NumSamples += b.Stats.NumSamples
+
+		if b.Compaction.Generation > res.Compaction.Generation {
+			res.Compaction.Generation = b.Compaction.Generation
+		}
+		for _, s := range b.Compaction.Sources {
+			sources[s] = struct{}{}
+		}
+		// If it's an in memory block, its ULID goes into the sources.
+		if b.Compaction.Generation == 0 {
+			sources[b.ULID] = struct{}{}
+		}
 	}
+	res.Compaction.Generation++
+
+	for s := range sources {
+		res.Compaction.Sources = append(res.Compaction.Sources, s)
+	}
+	sort.Slice(res.Compaction.Sources, func(i, j int) bool {
+		return res.Compaction.Sources[i].Compare(res.Compaction.Sources[j]) < 0
+	})
+
 	return res
 }
 
@@ -293,6 +311,7 @@ func (c *compactor) write(uid ulid.ULID, blocks ...Block) (err error) {
 // of the provided blocks. It returns meta information for the new block.
 func (c *compactor) populate(blocks []Block, indexw IndexWriter, chunkw ChunkWriter) (*BlockMeta, error) {
 	var set compactionSet
+	var metas []BlockMeta
 
 	for i, b := range blocks {
 		all, err := b.Index().Postings("", "")
@@ -309,6 +328,7 @@ func (c *compactor) populate(blocks []Block, indexw IndexWriter, chunkw ChunkWri
 		if err != nil {
 			return nil, err
 		}
+		metas = append(metas, b.Meta())
 	}
 
 	// We fully rebuild the postings list index from merged series.
@@ -316,7 +336,7 @@ func (c *compactor) populate(blocks []Block, indexw IndexWriter, chunkw ChunkWri
 		postings = &memPostings{m: make(map[term][]uint32, 512)}
 		values   = map[string]stringset{}
 		i        = uint32(0)
-		meta     = mergeBlockMetas(blocks...)
+		meta     = compactBlockMetas(metas...)
 	)
 
 	for set.Next() {