Break DB.Compact and DB.compactHead and DB.compactBlocks. Add DB.CompactHead.

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

tsdb/db.go

@@ -324,7 +324,7 @@ func (db *DBReadOnly) FlushWAL(dir string) error {
 	}
 	mint := head.MinTime()
 	maxt := head.MaxTime()
-	rh := &rangeHead{
+	rh := &RangeHead{
 		head: head,
 		mint: mint,
 		maxt: maxt,
@@ -685,41 +685,61 @@ func (db *DB) Compact() (err error) {
 		maxt := rangeForTimestamp(mint, db.head.chunkRange)
 
 		// Wrap head into a range that bounds all reads to it.
-		head := &rangeHead{
-			head: db.head,
-			mint: mint,
-			// We remove 1 millisecond from maxt because block
-			// intervals are half-open: [b.MinTime, b.MaxTime). But
-			// chunk intervals are closed: [c.MinTime, c.MaxTime];
-			// so in order to make sure that overlaps are evaluated
-			// consistently, we explicitly remove the last value
-			// from the block interval here.
-			maxt: maxt - 1,
-		}
-		uid, err := db.compactor.Write(db.dir, head, mint, maxt, nil)
-		if err != nil {
-			return errors.Wrap(err, "persist head block")
+		// We remove 1 millisecond from maxt because block
+		// intervals are half-open: [b.MinTime, b.MaxTime). But
+		// chunk intervals are closed: [c.MinTime, c.MaxTime];
+		// so in order to make sure that overlaps are evaluated
+		// consistently, we explicitly remove the last value
+		// from the block interval here.
+		head := NewRangeHead(db.head, mint, maxt-1)
+		if err := db.compactHead(head, mint, maxt); err != nil {
+			return err
 		}
+	}
 
-		runtime.GC()
+	return db.compactBlocks()
+}
 
-		if err := db.reload(); err != nil {
-			if err := os.RemoveAll(filepath.Join(db.dir, uid.String())); err != nil {
-				return errors.Wrapf(err, "delete persisted head block after failed db reload:%s", uid)
-			}
-			return errors.Wrap(err, "reload blocks")
+// CompactHead compacts the given the RangeHead.
+func (db *DB) CompactHead(head *RangeHead, mint, maxt int64) (err error) {
+	db.cmtx.Lock()
+	defer db.cmtx.Unlock()
+
+	return db.compactHead(head, mint, maxt)
+}
+
+// compactHead compacts the given the RangeHead.
+// The compaction mutex should be held before calling this method.
+func (db *DB) compactHead(head *RangeHead, mint, maxt int64) (err error) {
+	uid, err := db.compactor.Write(db.dir, head, mint, maxt, nil)
+	if err != nil {
+		return errors.Wrap(err, "persist head block")
+	}
+
+	runtime.GC()
+
+	if err := db.reload(); err != nil {
+		if err := os.RemoveAll(filepath.Join(db.dir, uid.String())); err != nil {
+			return errors.Wrapf(err, "delete persisted head block after failed db reload:%s", uid)
 		}
-		if (uid == ulid.ULID{}) {
-			// Compaction resulted in an empty block.
-			// Head truncating during db.reload() depends on the persisted blocks and
-			// in this case no new block will be persisted so manually truncate the head.
-			if err = db.head.Truncate(maxt); err != nil {
-				return errors.Wrap(err, "head truncate failed (in compact)")
-			}
+		return errors.Wrap(err, "reload blocks")
+	}
+	if (uid == ulid.ULID{}) {
+		// Compaction resulted in an empty block.
+		// Head truncating during db.reload() depends on the persisted blocks and
+		// in this case no new block will be persisted so manually truncate the head.
+		if err = db.head.Truncate(maxt); err != nil {
+			return errors.Wrap(err, "head truncate failed (in compact)")
 		}
-		runtime.GC()
 	}
+	runtime.GC()
+
+	return nil
+}
 
+// compactBlocks compacts all the eligible on-disk blocks.
+// The compaction mutex should be held before calling this method.
+func (db *DB) compactBlocks() (err error) {
 	// Check for compactions of multiple blocks.
 	for {
 		plan, err := db.compactor.Plan(db.dir)
@@ -1192,7 +1212,7 @@ func (db *DB) Snapshot(dir string, withHead bool) error {
 
 	mint := db.head.MinTime()
 	maxt := db.head.MaxTime()
-	head := &rangeHead{
+	head := &RangeHead{
 		head: db.head,
 		mint: mint,
 		maxt: maxt,
@@ -1221,7 +1241,7 @@ func (db *DB) Querier(mint, maxt int64) (Querier, error) {
 		}
 	}
 	if maxt >= db.head.MinTime() {
-		blocks = append(blocks, &rangeHead{
+		blocks = append(blocks, &RangeHead{
 			head: db.head,
 			mint: mint,
 			maxt: maxt,

tsdb/head.go

@@ -748,36 +748,45 @@ func (h *Head) initTime(t int64) (initialized bool) {
 	return true
 }
 
-type rangeHead struct {
+type RangeHead struct {
 	head       *Head
 	mint, maxt int64
 }
 
-func (h *rangeHead) Index() (IndexReader, error) {
+// NewRangeHead returns a *rangeHead.
+func NewRangeHead(head *Head, mint, maxt int64) *RangeHead {
+	return &RangeHead{
+		head: head,
+		mint: mint,
+		maxt: maxt,
+	}
+}
+
+func (h *RangeHead) Index() (IndexReader, error) {
 	return h.head.indexRange(h.mint, h.maxt), nil
 }
 
-func (h *rangeHead) Chunks() (ChunkReader, error) {
+func (h *RangeHead) Chunks() (ChunkReader, error) {
 	return h.head.chunksRange(h.mint, h.maxt), nil
 }
 
-func (h *rangeHead) Tombstones() (tombstones.Reader, error) {
+func (h *RangeHead) Tombstones() (tombstones.Reader, error) {
 	return h.head.tombstones, nil
 }
 
-func (h *rangeHead) MinTime() int64 {
+func (h *RangeHead) MinTime() int64 {
 	return h.mint
 }
 
-func (h *rangeHead) MaxTime() int64 {
+func (h *RangeHead) MaxTime() int64 {
 	return h.maxt
 }
 
-func (h *rangeHead) NumSeries() uint64 {
+func (h *RangeHead) NumSeries() uint64 {
 	return h.head.NumSeries()
 }
 
-func (h *rangeHead) Meta() BlockMeta {
+func (h *RangeHead) Meta() BlockMeta {
 	return BlockMeta{
 		MinTime: h.MinTime(),
 		MaxTime: h.MaxTime(),