Don't write empty blocks

compact.go

@@ -471,17 +471,24 @@ func (c *LeveledCompactor) write(dest string, meta *BlockMeta, blocks ...BlockRe
 		return errors.Wrap(err, "write compaction")
 	}
 
-	if err = writeMetaFile(tmp, meta); err != nil {
-		return errors.Wrap(err, "write merged meta")
-	}
-
 	if err = chunkw.Close(); err != nil {
 		return errors.Wrap(err, "close chunk writer")
 	}
 	if err = indexw.Close(); err != nil {
 		return errors.Wrap(err, "close index writer")
 	}
 
+	if meta.Stats.NumSamples == 0 {
+		if err := os.RemoveAll(tmp); err != nil {
+			return errors.Wrap(err, "remove tmp folder after empty block failed")
+		}
+		return nil
+	}
+
+	if err = writeMetaFile(tmp, meta); err != nil {
+		return errors.Wrap(err, "write merged meta")
+	}
+
 	// Create an empty tombstones file.
 	if err := writeTombstoneFile(tmp, NewMemTombstones()); err != nil {
 		return errors.Wrap(err, "write new tombstones file")

db.go

@@ -383,6 +383,22 @@ func (db *DB) compact() (changes bool, err error) {
 		if err := db.reload(); err != nil {
 			return changes, errors.Wrap(err, "reload blocks")
 		}
+		// After this is fixed https://github.com/prometheus/tsdb/issues/309,
+		// if the compaction of head did not create any new blocks (possible
+		// if the samples were deleted in that range), and if number of
+		// blocks are 0, db.reload() does not truncate head. Hence MinTime
+		// of head is not set properly. So only for that situation, we need
+		// to call db.head.Truncate(..) manually.
+		db.mtx.RLock()
+		l := len(db.blocks)
+		db.mtx.RUnlock()
+		if l == 0 {
+			err = db.head.Truncate(maxt)
+			if err != nil {
+				return changes, errors.Wrap(err, "head truncate failed (in compact)")
+
+			}
+		}
 		runtime.GC()
 	}
 

db_test.go

@@ -1301,3 +1301,53 @@ func TestInitializeHeadTimestamp(t *testing.T) {
 		testutil.Equals(t, int64(15000), db.head.MaxTime())
 	})
 }
+
+func TestNoEmptyBlock(t *testing.T) {
+	db, close := openTestDB(t, nil)
+	defer close()
+	defer db.Close()
+
+	// Test no blocks after compact with empty head.
+	_, err := db.compact()
+	testutil.Ok(t, err)
+	testutil.Equals(t, 0, len(db.blocks))
+
+	blockRange := DefaultOptions.BlockRanges[0]
+	label := labels.FromStrings("foo", "bar")
+
+	app := db.Appender()
+	for i := int64(0); i < 3; i++ {
+		_, err := app.Add(label, i*blockRange, 0)
+		testutil.Ok(t, err)
+		_, err = app.Add(label, i*blockRange+1000, 0)
+		testutil.Ok(t, err)
+	}
+	err = app.Commit()
+	testutil.Ok(t, err)
+
+	// Test no blocks after deleting all samples from head.
+	testutil.Ok(t, db.Delete(math.MinInt64, math.MaxInt64, labels.NewEqualMatcher("foo", "bar")))
+	_, err = db.compact()
+	testutil.Ok(t, err)
+	testutil.Equals(t, 0, len(db.blocks))
+
+	app = db.Appender()
+	for i := int64(3); i < 6; i++ {
+		_, err := app.Add(label, i*blockRange, 0)
+		testutil.Ok(t, err)
+		_, err = app.Add(label, i*blockRange+1000, 0)
+		testutil.Ok(t, err)
+	}
+	err = app.Commit()
+	testutil.Ok(t, err)
+
+	_, err = db.compact()
+	testutil.Ok(t, err)
+	testutil.Equals(t, 1, len(db.blocks))
+
+	// No blocks after deleting all samples from disk.
+	testutil.Ok(t, db.Delete(math.MinInt64, math.MaxInt64, labels.NewEqualMatcher("foo", "bar")))
+	_, err = db.compact()
+	testutil.Ok(t, err)
+	testutil.Equals(t, 0, len(db.blocks))
+}