diff --git a/cmd/prometheus/config.go b/cmd/prometheus/config.go
index 0e75080c5d..3fcf917ce2 100644
--- a/cmd/prometheus/config.go
+++ b/cmd/prometheus/config.go
@@ -126,9 +126,13 @@ func init() {
 		"Maximum duration compacted blocks may span.",
 	)
 	cfg.fs.IntVar(
-		&cfg.tsdb.AppendableBlocks, "storage.tsdb.AppendableBlocks", 2,
+		&cfg.tsdb.AppendableBlocks, "storage.tsdb.appendable-blocks", 2,
 		"Number of head blocks that can be appended to.",
 	)
+	cfg.fs.DurationVar(
+		&cfg.tsdb.Retention, "storage.tsdb.retention", 15*24*time.Hour,
+		"How long to retain samples in the storage.",
+	)
 	cfg.fs.StringVar(
 		&cfg.localStorageEngine, "storage.local.engine", "persisted",
 		"Local storage engine. Supported values are: 'persisted' (full local storage with on-disk persistence) and 'none' (no local storage).",
diff --git a/cmd/prometheus/main.go b/cmd/prometheus/main.go
index 39aecfdbff..8f2365af43 100644
--- a/cmd/prometheus/main.go
+++ b/cmd/prometheus/main.go
@@ -70,13 +70,6 @@ func Main() int {
 		return 0
 	}
 
-	// go func() {
-	// 	for {
-	// 		time.Sleep(30 * time.Second)
-	// 		debug.FreeOSMemory()
-	// 	}
-	// }()
-
 	log.Infoln("Starting prometheus", version.Info())
 	log.Infoln("Build context", version.BuildContext())
 
diff --git a/storage/tsdb/tsdb.go b/storage/tsdb/tsdb.go
index 8351252071..a19bda967f 100644
--- a/storage/tsdb/tsdb.go
+++ b/storage/tsdb/tsdb.go
@@ -34,15 +34,19 @@ type Options struct {
 	// After a new block is started for timestamp t0 or higher, appends with
 	// timestamps as early as t0 - (n-1) * MinBlockDuration are valid.
 	AppendableBlocks int
+
+	// Duration for how long to retain data.
+	Retention time.Duration
 }
 
 // Open returns a new storage backed by a tsdb database.
 func Open(path string, r prometheus.Registerer, opts *Options) (storage.Storage, error) {
 	db, err := tsdb.Open(path, nil, r, &tsdb.Options{
-		WALFlushInterval: 10 * time.Second,
-		MinBlockDuration: uint64(opts.MinBlockDuration.Seconds() * 1000),
-		MaxBlockDuration: uint64(opts.MaxBlockDuration.Seconds() * 1000),
-		AppendableBlocks: opts.AppendableBlocks,
+		WALFlushInterval:  10 * time.Second,
+		MinBlockDuration:  uint64(opts.MinBlockDuration.Seconds() * 1000),
+		MaxBlockDuration:  uint64(opts.MaxBlockDuration.Seconds() * 1000),
+		AppendableBlocks:  opts.AppendableBlocks,
+		RetentionDuration: uint64(opts.Retention.Seconds() * 1000),
 	})
 	if err != nil {
 		return nil, err
diff --git a/vendor/github.com/fabxc/tsdb/chunks.go b/vendor/github.com/fabxc/tsdb/chunks.go
index c0c7954a6e..b3aaeb206d 100644
--- a/vendor/github.com/fabxc/tsdb/chunks.go
+++ b/vendor/github.com/fabxc/tsdb/chunks.go
@@ -36,7 +36,7 @@ type ChunkWriter interface {
 	// must be populated.
 	// After returning successfully, the Ref fields in the ChunkMetas
 	// is set and can be used to retrieve the chunks from the written data.
-	WriteChunks(chunks ...ChunkMeta) error
+	WriteChunks(chunks ...*ChunkMeta) error
 
 	// Close writes any required finalization and closes the resources
 	// associated with the underlying writer.
@@ -156,7 +156,7 @@ func (w *chunkWriter) write(wr io.Writer, b []byte) error {
 	return err
 }
 
-func (w *chunkWriter) WriteChunks(chks ...ChunkMeta) error {
+func (w *chunkWriter) WriteChunks(chks ...*ChunkMeta) error {
 	// Calculate maximum space we need and cut a new segment in case
 	// we don't fit into the current one.
 	maxLen := int64(binary.MaxVarintLen32)
@@ -184,9 +184,7 @@ func (w *chunkWriter) WriteChunks(chks ...ChunkMeta) error {
 	}
 	seq := uint64(w.seq()) << 32
 
-	for i := range chks {
-		chk := &chks[i]
-
+	for _, chk := range chks {
 		chk.Ref = seq | uint64(w.n)
 
 		n = binary.PutUvarint(b, uint64(len(chk.Chunk.Bytes())))
diff --git a/vendor/github.com/fabxc/tsdb/compact.go b/vendor/github.com/fabxc/tsdb/compact.go
index 573e9b440a..a1d7b1e5c5 100644
--- a/vendor/github.com/fabxc/tsdb/compact.go
+++ b/vendor/github.com/fabxc/tsdb/compact.go
@@ -334,7 +334,7 @@ func (c *compactor) populate(blocks []Block, indexw IndexWriter, chunkw ChunkWri
 
 type compactionSet interface {
 	Next() bool
-	At() (labels.Labels, []ChunkMeta)
+	At() (labels.Labels, []*ChunkMeta)
 	Err() error
 }
 
@@ -344,7 +344,7 @@ type compactionSeriesSet struct {
 	chunks ChunkReader
 
 	l   labels.Labels
-	c   []ChunkMeta
+	c   []*ChunkMeta
 	err error
 }
 
@@ -365,9 +365,7 @@ func (c *compactionSeriesSet) Next() bool {
 	if c.err != nil {
 		return false
 	}
-	for i := range c.c {
-		chk := &c.c[i]
-
+	for _, chk := range c.c {
 		chk.Chunk, c.err = c.chunks.Chunk(chk.Ref)
 		if c.err != nil {
 			return false
@@ -384,7 +382,7 @@ func (c *compactionSeriesSet) Err() error {
 	return c.p.Err()
 }
 
-func (c *compactionSeriesSet) At() (labels.Labels, []ChunkMeta) {
+func (c *compactionSeriesSet) At() (labels.Labels, []*ChunkMeta) {
 	return c.l, c.c
 }
 
@@ -393,12 +391,12 @@ type compactionMerger struct {
 
 	aok, bok bool
 	l        labels.Labels
-	c        []ChunkMeta
+	c        []*ChunkMeta
 }
 
 type compactionSeries struct {
 	labels labels.Labels
-	chunks []ChunkMeta
+	chunks []*ChunkMeta
 }
 
 func newCompactionMerger(a, b compactionSet) (*compactionMerger, error) {
@@ -459,7 +457,7 @@ func (c *compactionMerger) Err() error {
 	return c.b.Err()
 }
 
-func (c *compactionMerger) At() (labels.Labels, []ChunkMeta) {
+func (c *compactionMerger) At() (labels.Labels, []*ChunkMeta) {
 	return c.l, c.c
 }
 
diff --git a/vendor/github.com/fabxc/tsdb/db.go b/vendor/github.com/fabxc/tsdb/db.go
index 7124ce1067..ec0f0a7018 100644
--- a/vendor/github.com/fabxc/tsdb/db.go
+++ b/vendor/github.com/fabxc/tsdb/db.go
@@ -207,10 +207,13 @@ func (db *DB) run() {
 
 			var merr MultiError
 
-			changes, err := db.compact()
+			changes1, err := db.retentionCutoff()
 			merr.Add(err)
 
-			if changes {
+			changes2, err := db.compact()
+			merr.Add(err)
+
+			if changes1 || changes2 {
 				merr.Add(db.reloadBlocks())
 			}
 			if err := merr.Err(); err != nil {
@@ -223,11 +226,31 @@ func (db *DB) run() {
 	}
 }
 
+func (db *DB) retentionCutoff() (bool, error) {
+	if db.opts.RetentionDuration == 0 {
+		return false, nil
+	}
+
+	db.mtx.RLock()
+	defer db.mtx.RUnlock()
+
+	// We don't count the span covered by head blocks towards the
+	// retention time as it generally makes up a fraction of it.
+	if len(db.persisted) == 0 {
+		return false, nil
+	}
+
+	last := db.persisted[len(db.persisted)-1]
+	mint := last.Meta().MaxTime - int64(db.opts.RetentionDuration)
+
+	return retentionCutoff(db.dir, mint)
+}
+
 func (db *DB) compact() (changes bool, err error) {
-	// Check whether we have pending head blocks that are ready to be persisted.
-	// They have the highest priority.
 	db.headmtx.RLock()
 
+	// Check whether we have pending head blocks that are ready to be persisted.
+	// They have the highest priority.
 	var singles []*headBlock
 
 	// Collect head blocks that are ready for compaction. Write them after
@@ -297,38 +320,40 @@ Loop:
 	return changes, nil
 }
 
-// func (db *DB) retentionCutoff() error {
-// 	if db.opts.RetentionDuration == 0 {
-// 		return nil
-// 	}
-// 	h := db.heads[len(db.heads)-1]
-// 	t := h.meta.MinTime - int64(db.opts.RetentionDuration)
+// retentionCutoff deletes all directories of blocks in dir that are strictly
+// before mint.
+func retentionCutoff(dir string, mint int64) (bool, error) {
+	dirs, err := blockDirs(dir)
+	if err != nil {
+		return false, errors.Wrapf(err, "list block dirs %s", dir)
+	}
 
-// 	var (
-// 		blocks = db.blocks()
-// 		i      int
-// 		b      Block
-// 	)
-// 	for i, b = range blocks {
-// 		if b.Meta().MinTime >= t {
-// 			break
-// 		}
-// 	}
-// 	if i <= 1 {
-// 		return nil
-// 	}
-// 	db.logger.Log("msg", "retention cutoff", "idx", i-1)
-// 	db.removeBlocks(0, i)
+	changes := false
 
-// 	for _, b := range blocks[:i] {
-// 		if err := os.RemoveAll(b.Dir()); err != nil {
-// 			return errors.Wrap(err, "removing old block")
-// 		}
-// 	}
-// 	return nil
-// }
+	for _, dir := range dirs {
+		meta, err := readMetaFile(dir)
+		if err != nil {
+			return changes, errors.Wrapf(err, "read block meta %s", dir)
+		}
+		// The first block we encounter marks that we crossed the boundary
+		// of deletable blocks.
+		if meta.MaxTime >= mint {
+			break
+		}
+		changes = true
+
+		if err := os.RemoveAll(dir); err != nil {
+			return changes, err
+		}
+	}
+
+	return changes, nil
+}
 
 func (db *DB) reloadBlocks() error {
+	var cs []io.Closer
+	defer closeAll(cs...)
+
 	db.mtx.Lock()
 	defer db.mtx.Unlock()
 
@@ -381,11 +406,11 @@ func (db *DB) reloadBlocks() error {
 		seqBlocks[meta.Sequence] = b
 	}
 
+	// Close all blocks that we no longer need. They are closed after returning all
+	// locks to avoid questionable locking order.
 	for seq, b := range db.seqBlocks {
 		if nb, ok := seqBlocks[seq]; !ok || nb != b {
-			if err := b.Close(); err != nil {
-				return errors.Wrapf(err, "closing removed block %d", b.Meta().Sequence)
-			}
+			cs = append(cs, b)
 		}
 	}
 
@@ -401,9 +426,8 @@ func (db *DB) Close() error {
 	close(db.stopc)
 	<-db.donec
 
-	// Lock mutex and leave it locked so we panic if there's a bug causing
-	// the block to be used afterwards.
 	db.mtx.Lock()
+	defer db.mtx.Unlock()
 
 	var g errgroup.Group
 
@@ -427,14 +451,20 @@ func (db *DB) Appender() Appender {
 	db.mtx.RLock()
 	a := &dbAppender{db: db}
 
+	// Only instantiate appender after returning the headmtx to avoid
+	// questionable locking order.
 	db.headmtx.RLock()
 
-	for _, b := range db.appendable() {
-		a.heads = append(a.heads, b.Appender().(*headAppender))
-	}
+	app := db.appendable()
+	heads := make([]*headBlock, len(app))
+	copy(heads, app)
 
 	db.headmtx.RUnlock()
 
+	for _, b := range heads {
+		a.heads = append(a.heads, b.Appender().(*headAppender))
+	}
+
 	return a
 }
 
@@ -486,24 +516,30 @@ func (a *dbAppender) appenderFor(t int64) (*headAppender, error) {
 	if len(a.heads) == 0 || t >= a.heads[len(a.heads)-1].meta.MaxTime {
 		a.db.headmtx.Lock()
 
+		var newHeads []*headBlock
+
 		if err := a.db.ensureHead(t); err != nil {
 			a.db.headmtx.Unlock()
 			return nil, err
 		}
 		if len(a.heads) == 0 {
-			for _, b := range a.db.appendable() {
-				a.heads = append(a.heads, b.Appender().(*headAppender))
-			}
+			newHeads = append(newHeads, a.db.appendable()...)
 		} else {
 			maxSeq := a.heads[len(a.heads)-1].meta.Sequence
 			for _, b := range a.db.appendable() {
 				if b.meta.Sequence > maxSeq {
-					a.heads = append(a.heads, b.Appender().(*headAppender))
+					newHeads = append(newHeads, b)
 				}
 			}
 		}
 
 		a.db.headmtx.Unlock()
+
+		// Instantiate appenders after returning headmtx to avoid questionable
+		// locking order.
+		for _, b := range newHeads {
+			a.heads = append(a.heads, b.Appender().(*headAppender))
+		}
 	}
 	for i := len(a.heads) - 1; i >= 0; i-- {
 		if h := a.heads[i]; t >= h.meta.MinTime {
diff --git a/vendor/github.com/fabxc/tsdb/head.go b/vendor/github.com/fabxc/tsdb/head.go
index 211cadf775..eed2ff2222 100644
--- a/vendor/github.com/fabxc/tsdb/head.go
+++ b/vendor/github.com/fabxc/tsdb/head.go
@@ -10,7 +10,6 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/bradfitz/slice"
 	"github.com/fabxc/tsdb/chunks"
 	"github.com/fabxc/tsdb/labels"
 	"github.com/go-kit/kit/log"
@@ -43,13 +42,11 @@ type headBlock struct {
 	wal        *WAL
 
 	activeWriters uint64
+	closed        bool
 
 	// descs holds all chunk descs for the head block. Each chunk implicitly
 	// is assigned the index as its ID.
 	series []*memSeries
-	// mapping maps a series ID to its position in an ordered list
-	// of all series. The orderDirty flag indicates that it has gone stale.
-	mapper *positionMapper
 	// hashes contains a collision map of label set hashes of chunks
 	// to their chunk descs.
 	hashes map[uint64][]*memSeries
@@ -105,7 +102,6 @@ func openHeadBlock(dir string, l log.Logger) (*headBlock, error) {
 		hashes:   map[uint64][]*memSeries{},
 		values:   map[string]stringset{},
 		postings: &memPostings{m: make(map[term][]uint32)},
-		mapper:   newPositionMapper(nil),
 		meta:     *meta,
 	}
 
@@ -131,8 +127,6 @@ func openHeadBlock(dir string, l log.Logger) (*headBlock, error) {
 		return nil, errors.Wrap(err, "consume WAL")
 	}
 
-	h.updateMapping()
-
 	return h, nil
 }
 
@@ -144,9 +138,8 @@ func (h *headBlock) inBounds(t int64) bool {
 
 // Close syncs all data and closes underlying resources of the head block.
 func (h *headBlock) Close() error {
-	// Lock mutex and leave it locked so we panic if there's a bug causing
-	// the block to be used afterwards.
 	h.mtx.Lock()
+	defer h.mtx.Unlock()
 
 	if err := h.wal.Close(); err != nil {
 		return errors.Wrapf(err, "close WAL for head %s", h.dir)
@@ -163,6 +156,8 @@ func (h *headBlock) Close() error {
 	if meta.ULID == h.meta.ULID {
 		return writeMetaFile(h.dir, &h.meta)
 	}
+
+	h.closed = true
 	return nil
 }
 
@@ -182,6 +177,10 @@ func (h *headBlock) Appender() Appender {
 	atomic.AddUint64(&h.activeWriters, 1)
 
 	h.mtx.RLock()
+
+	if h.closed {
+		panic(fmt.Sprintf("block %s already closed", h.dir))
+	}
 	return &headAppender{headBlock: h, samples: getHeadAppendBuffer()}
 }
 
@@ -451,7 +450,7 @@ func (h *headIndexReader) Postings(name, value string) (Postings, error) {
 }
 
 // Series returns the series for the given reference.
-func (h *headIndexReader) Series(ref uint32) (labels.Labels, []ChunkMeta, error) {
+func (h *headIndexReader) Series(ref uint32) (labels.Labels, []*ChunkMeta, error) {
 	h.mtx.RLock()
 	defer h.mtx.RUnlock()
 
@@ -459,13 +458,13 @@ func (h *headIndexReader) Series(ref uint32) (labels.Labels, []ChunkMeta, error)
 		return nil, nil, ErrNotFound
 	}
 	s := h.series[ref]
-	metas := make([]ChunkMeta, 0, len(s.chunks))
+	metas := make([]*ChunkMeta, 0, len(s.chunks))
 
 	s.mtx.RLock()
 	defer s.mtx.RUnlock()
 
 	for i, c := range s.chunks {
-		metas = append(metas, ChunkMeta{
+		metas = append(metas, &ChunkMeta{
 			MinTime: c.minTime,
 			MaxTime: c.maxTime,
 			Ref:     (uint64(ref) << 32) | uint64(i),
@@ -527,43 +526,26 @@ func (h *headBlock) create(hash uint64, lset labels.Labels) *memSeries {
 	return s
 }
 
-func (h *headBlock) updateMapping() {
-	h.mtx.RLock()
-
-	if h.mapper.sortable != nil && h.mapper.Len() == len(h.series) {
-		h.mtx.RUnlock()
-		return
-	}
-
-	series := make([]*memSeries, len(h.series))
-	copy(series, h.series)
-
-	h.mtx.RUnlock()
-
-	s := slice.SortInterface(series, func(i, j int) bool {
-		return labels.Compare(series[i].lset, series[j].lset) < 0
-	})
-
-	h.mapper.update(s)
-}
-
 // remapPostings changes the order of the postings from their ID to the ordering
 // of the series they reference.
 // Returned postings have no longer monotonic IDs and MUST NOT be used for regular
 // postings set operations, i.e. intersect and merge.
 func (h *headBlock) remapPostings(p Postings) Postings {
-	list, err := expandPostings(p)
-	if err != nil {
-		return errPostings{err: err}
+	// Expand the postings but only up until the point where the mapper
+	// covers existing metrics.
+	ep := make([]uint32, 0, 64)
+
+	for p.Next() {
+		ep = append(ep, p.At())
+	}
+	if err := p.Err(); err != nil {
+		return errPostings{err: errors.Wrap(err, "expand postings")}
 	}
 
-	h.mapper.mtx.Lock()
-	defer h.mapper.mtx.Unlock()
-
-	h.updateMapping()
-	h.mapper.Sort(list)
-
-	return newListPostings(list)
+	sort.Slice(ep, func(i, j int) bool {
+		return labels.Compare(h.series[i].lset, h.series[j].lset) < 0
+	})
+	return newListPostings(ep)
 }
 
 type memSeries struct {
@@ -675,50 +657,3 @@ func (it *memSafeIterator) At() (int64, float64) {
 	s := it.buf[4-(it.total-it.i)]
 	return s.t, s.v
 }
-
-// positionMapper stores a position mapping from unsorted to
-// sorted indices of a sortable collection.
-type positionMapper struct {
-	mtx      sync.RWMutex
-	sortable sort.Interface
-	iv, fw   []int
-}
-
-func newPositionMapper(s sort.Interface) *positionMapper {
-	m := &positionMapper{}
-	if s != nil {
-		m.update(s)
-	}
-	return m
-}
-
-func (m *positionMapper) Len() int           { return m.sortable.Len() }
-func (m *positionMapper) Less(i, j int) bool { return m.sortable.Less(i, j) }
-
-func (m *positionMapper) Swap(i, j int) {
-	m.sortable.Swap(i, j)
-
-	m.iv[i], m.iv[j] = m.iv[j], m.iv[i]
-}
-
-func (m *positionMapper) Sort(l []uint32) {
-	slice.Sort(l, func(i, j int) bool {
-		return m.fw[l[i]] < m.fw[l[j]]
-	})
-}
-
-func (m *positionMapper) update(s sort.Interface) {
-	m.sortable = s
-
-	m.iv = make([]int, s.Len())
-	m.fw = make([]int, s.Len())
-
-	for i := range m.iv {
-		m.iv[i] = i
-	}
-	sort.Sort(m)
-
-	for i, k := range m.iv {
-		m.fw[k] = i
-	}
-}
diff --git a/vendor/github.com/fabxc/tsdb/index.go b/vendor/github.com/fabxc/tsdb/index.go
index 23771f035e..f957085763 100644
--- a/vendor/github.com/fabxc/tsdb/index.go
+++ b/vendor/github.com/fabxc/tsdb/index.go
@@ -33,7 +33,7 @@ type IndexWriter interface {
 	// of chunks that the index can reference.
 	// The reference number is used to resolve a series against the postings
 	// list iterator. It only has to be available during the write processing.
-	AddSeries(ref uint32, l labels.Labels, chunks ...ChunkMeta) error
+	AddSeries(ref uint32, l labels.Labels, chunks ...*ChunkMeta) error
 
 	// WriteLabelIndex serializes an index from label names to values.
 	// The passed in values chained tuples of strings of the length of names.
@@ -49,8 +49,8 @@ type IndexWriter interface {
 
 type indexWriterSeries struct {
 	labels labels.Labels
-	chunks []ChunkMeta // series file offset of chunks
-	offset uint32      // index file offset of series reference
+	chunks []*ChunkMeta // series file offset of chunks
+	offset uint32       // index file offset of series reference
 }
 
 // indexWriter implements the IndexWriter interface for the standard
@@ -142,7 +142,7 @@ func (w *indexWriter) writeMeta() error {
 	return w.write(w.bufw, b[:])
 }
 
-func (w *indexWriter) AddSeries(ref uint32, lset labels.Labels, chunks ...ChunkMeta) error {
+func (w *indexWriter) AddSeries(ref uint32, lset labels.Labels, chunks ...*ChunkMeta) error {
 	if _, ok := w.series[ref]; ok {
 		return errors.Errorf("series with reference %d already added", ref)
 	}
@@ -419,7 +419,7 @@ type IndexReader interface {
 	Postings(name, value string) (Postings, error)
 
 	// Series returns the series for the given reference.
-	Series(ref uint32) (labels.Labels, []ChunkMeta, error)
+	Series(ref uint32) (labels.Labels, []*ChunkMeta, error)
 
 	// LabelIndices returns the label pairs for which indices exist.
 	LabelIndices() ([][]string, error)
@@ -599,7 +599,7 @@ func (r *indexReader) LabelIndices() ([][]string, error) {
 	return res, nil
 }
 
-func (r *indexReader) Series(ref uint32) (labels.Labels, []ChunkMeta, error) {
+func (r *indexReader) Series(ref uint32) (labels.Labels, []*ChunkMeta, error) {
 	k, n := binary.Uvarint(r.b[ref:])
 	if n < 1 {
 		return nil, nil, errors.Wrap(errInvalidSize, "number of labels")
@@ -642,7 +642,7 @@ func (r *indexReader) Series(ref uint32) (labels.Labels, []ChunkMeta, error) {
 	}
 
 	b = b[n:]
-	chunks := make([]ChunkMeta, 0, k)
+	chunks := make([]*ChunkMeta, 0, k)
 
 	for i := 0; i < int(k); i++ {
 		firstTime, n := binary.Varint(b)
@@ -663,7 +663,7 @@ func (r *indexReader) Series(ref uint32) (labels.Labels, []ChunkMeta, error) {
 		}
 		b = b[n:]
 
-		chunks = append(chunks, ChunkMeta{
+		chunks = append(chunks, &ChunkMeta{
 			Ref:     o,
 			MinTime: firstTime,
 			MaxTime: lastTime,
diff --git a/vendor/github.com/fabxc/tsdb/querier.go b/vendor/github.com/fabxc/tsdb/querier.go
index a397b9a632..c027a8dc0e 100644
--- a/vendor/github.com/fabxc/tsdb/querier.go
+++ b/vendor/github.com/fabxc/tsdb/querier.go
@@ -66,6 +66,12 @@ func (s *DB) Querier(mint, maxt int64) Querier {
 
 		// TODO(fabxc): find nicer solution.
 		if hb, ok := b.(*headBlock); ok {
+			// TODO(fabxc): temporary refactored.
+			hb.mtx.RLock()
+			if hb.closed {
+				panic(fmt.Sprintf("block %s already closed", hb.dir))
+			}
+			hb.mtx.RUnlock()
 			q.postingsMapper = hb.remapPostings
 		}
 
@@ -109,7 +115,7 @@ func (q *querier) Select(ms ...labels.Matcher) SeriesSet {
 	r := q.blocks[0].Select(ms...)
 
 	for _, s := range q.blocks[1:] {
-		r = newPartitionSeriesSet(r, s.Select(ms...))
+		r = newMergedSeriesSet(r, s.Select(ms...))
 	}
 	return r
 }
@@ -135,15 +141,6 @@ type blockQuerier struct {
 	mint, maxt int64
 }
 
-func newBlockQuerier(ix IndexReader, c ChunkReader, mint, maxt int64) *blockQuerier {
-	return &blockQuerier{
-		mint:   mint,
-		maxt:   maxt,
-		index:  ix,
-		chunks: c,
-	}
-}
-
 func (q *blockQuerier) Select(ms ...labels.Matcher) SeriesSet {
 	var (
 		its    []Postings
@@ -282,39 +279,14 @@ func (nopSeriesSet) At() Series { return nil }
 func (nopSeriesSet) Err() error { return nil }
 
 type mergedSeriesSet struct {
-	sets []SeriesSet
-
-	cur int
-	err error
-}
-
-func (s *mergedSeriesSet) At() Series { return s.sets[s.cur].At() }
-func (s *mergedSeriesSet) Err() error { return s.sets[s.cur].Err() }
-
-func (s *mergedSeriesSet) Next() bool {
-	// TODO(fabxc): We just emit the sets one after one. They are each
-	// lexicographically sorted. Should we emit their union sorted too?
-	if s.sets[s.cur].Next() {
-		return true
-	}
-
-	if s.cur == len(s.sets)-1 {
-		return false
-	}
-	s.cur++
-
-	return s.Next()
-}
-
-type partitionSeriesSet struct {
 	a, b SeriesSet
 
 	cur          Series
 	adone, bdone bool
 }
 
-func newPartitionSeriesSet(a, b SeriesSet) *partitionSeriesSet {
-	s := &partitionSeriesSet{a: a, b: b}
+func newMergedSeriesSet(a, b SeriesSet) *mergedSeriesSet {
+	s := &mergedSeriesSet{a: a, b: b}
 	// Initialize first elements of both sets as Next() needs
 	// one element look-ahead.
 	s.adone = !s.a.Next()
@@ -323,18 +295,18 @@ func newPartitionSeriesSet(a, b SeriesSet) *partitionSeriesSet {
 	return s
 }
 
-func (s *partitionSeriesSet) At() Series {
+func (s *mergedSeriesSet) At() Series {
 	return s.cur
 }
 
-func (s *partitionSeriesSet) Err() error {
+func (s *mergedSeriesSet) Err() error {
 	if s.a.Err() != nil {
 		return s.a.Err()
 	}
 	return s.b.Err()
 }
 
-func (s *partitionSeriesSet) compare() int {
+func (s *mergedSeriesSet) compare() int {
 	if s.adone {
 		return 1
 	}
@@ -344,7 +316,7 @@ func (s *partitionSeriesSet) compare() int {
 	return labels.Compare(s.a.At().Labels(), s.b.At().Labels())
 }
 
-func (s *partitionSeriesSet) Next() bool {
+func (s *mergedSeriesSet) Next() bool {
 	if s.adone && s.bdone || s.Err() != nil {
 		return false
 	}
@@ -370,7 +342,7 @@ func (s *partitionSeriesSet) Next() bool {
 
 type chunkSeriesSet interface {
 	Next() bool
-	At() (labels.Labels, []ChunkMeta)
+	At() (labels.Labels, []*ChunkMeta)
 	Err() error
 }
 
@@ -382,12 +354,12 @@ type baseChunkSeries struct {
 	absent []string // labels that must be unset in results.
 
 	lset labels.Labels
-	chks []ChunkMeta
+	chks []*ChunkMeta
 	err  error
 }
 
-func (s *baseChunkSeries) At() (labels.Labels, []ChunkMeta) { return s.lset, s.chks }
-func (s *baseChunkSeries) Err() error                       { return s.err }
+func (s *baseChunkSeries) At() (labels.Labels, []*ChunkMeta) { return s.lset, s.chks }
+func (s *baseChunkSeries) Err() error                        { return s.err }
 
 func (s *baseChunkSeries) Next() bool {
 Outer:
@@ -425,20 +397,18 @@ type populatedChunkSeries struct {
 	mint, maxt int64
 
 	err  error
-	chks []ChunkMeta
+	chks []*ChunkMeta
 	lset labels.Labels
 }
 
-func (s *populatedChunkSeries) At() (labels.Labels, []ChunkMeta) { return s.lset, s.chks }
-func (s *populatedChunkSeries) Err() error                       { return s.err }
+func (s *populatedChunkSeries) At() (labels.Labels, []*ChunkMeta) { return s.lset, s.chks }
+func (s *populatedChunkSeries) Err() error                        { return s.err }
 
 func (s *populatedChunkSeries) Next() bool {
 	for s.set.Next() {
 		lset, chks := s.set.At()
 
-		for i := range chks {
-			c := &chks[i]
-
+		for i, c := range chks {
 			if c.MaxTime < s.mint {
 				chks = chks[1:]
 				continue
@@ -493,7 +463,7 @@ func (s *blockSeriesSet) Err() error { return s.err }
 // time series data.
 type chunkSeries struct {
 	labels labels.Labels
-	chunks []ChunkMeta // in-order chunk refs
+	chunks []*ChunkMeta // in-order chunk refs
 }
 
 func (s *chunkSeries) Labels() labels.Labels {
@@ -587,13 +557,13 @@ func (it *chainedSeriesIterator) Err() error {
 // chunkSeriesIterator implements a series iterator on top
 // of a list of time-sorted, non-overlapping chunks.
 type chunkSeriesIterator struct {
-	chunks []ChunkMeta
+	chunks []*ChunkMeta
 
 	i   int
 	cur chunks.Iterator
 }
 
-func newChunkSeriesIterator(cs []ChunkMeta) *chunkSeriesIterator {
+func newChunkSeriesIterator(cs []*ChunkMeta) *chunkSeriesIterator {
 	return &chunkSeriesIterator{
 		chunks: cs,
 		i:      0,
diff --git a/vendor/github.com/fabxc/tsdb/wal.go b/vendor/github.com/fabxc/tsdb/wal.go
index b06425e076..2a49dcf41e 100644
--- a/vendor/github.com/fabxc/tsdb/wal.go
+++ b/vendor/github.com/fabxc/tsdb/wal.go
@@ -63,7 +63,7 @@ const (
 
 // OpenWAL opens or creates a write ahead log in the given directory.
 // The WAL must be read completely before new data is written.
-func OpenWAL(dir string, l log.Logger, flushInterval time.Duration) (*WAL, error) {
+func OpenWAL(dir string, logger log.Logger, flushInterval time.Duration) (*WAL, error) {
 	dir = filepath.Join(dir, walDirName)
 
 	if err := os.MkdirAll(dir, 0777); err != nil {
@@ -73,10 +73,13 @@ func OpenWAL(dir string, l log.Logger, flushInterval time.Duration) (*WAL, error
 	if err != nil {
 		return nil, err
 	}
+	if logger == nil {
+		logger = log.NewNopLogger()
+	}
 
 	w := &WAL{
 		dirFile:       df,
-		logger:        l,
+		logger:        logger,
 		flushInterval: flushInterval,
 		donec:         make(chan struct{}),
 		stopc:         make(chan struct{}),
@@ -95,11 +98,7 @@ func OpenWAL(dir string, l log.Logger, flushInterval time.Duration) (*WAL, error
 // Reader returns a new reader over the the write ahead log data.
 // It must be completely consumed before writing to the WAL.
 func (w *WAL) Reader() *WALReader {
-	var rs []io.ReadCloser
-	for _, f := range w.files {
-		rs = append(rs, f)
-	}
-	return NewWALReader(rs...)
+	return NewWALReader(w.logger, w)
 }
 
 // Log writes a batch of new series labels and samples to the log.
@@ -126,21 +125,15 @@ func (w *WAL) initSegments() error {
 	if len(fns) == 0 {
 		return nil
 	}
-	if len(fns) > 1 {
-		for _, fn := range fns[:len(fns)-1] {
-			f, err := os.Open(fn)
-			if err != nil {
-				return err
-			}
-			w.files = append(w.files, f)
+	// We must open all file in read mode as we may have to truncate along
+	// the way and any file may become the tail.
+	for _, fn := range fns {
+		f, err := os.OpenFile(fn, os.O_RDWR, 0666)
+		if err != nil {
+			return err
 		}
+		w.files = append(w.files, f)
 	}
-	// The most recent WAL file is the one we have to keep appending to.
-	f, err := os.OpenFile(fns[len(fns)-1], os.O_RDWR, 0666)
-	if err != nil {
-		return err
-	}
-	w.files = append(w.files, f)
 
 	// Consume and validate meta headers.
 	for _, f := range w.files {
@@ -275,7 +268,7 @@ func (w *WAL) Close() error {
 	// On opening, a WAL must be fully consumed once. Afterwards
 	// only the current segment will still be open.
 	if tf := w.tail(); tf != nil {
-		return tf.Close()
+		return errors.Wrapf(tf.Close(), "closing WAL tail %s", tf.Name())
 	}
 	return nil
 }
@@ -413,7 +406,9 @@ func (w *WAL) encodeSamples(samples []refdSample) error {
 
 // WALReader decodes and emits write ahead log entries.
 type WALReader struct {
-	rs    []io.ReadCloser
+	logger log.Logger
+
+	wal   *WAL
 	cur   int
 	buf   []byte
 	crc32 hash.Hash32
@@ -424,12 +419,17 @@ type WALReader struct {
 }
 
 // NewWALReader returns a new WALReader over the sequence of the given ReadClosers.
-func NewWALReader(rs ...io.ReadCloser) *WALReader {
-	return &WALReader{
-		rs:    rs,
-		buf:   make([]byte, 0, 128*4096),
-		crc32: crc32.New(crc32.MakeTable(crc32.Castagnoli)),
+func NewWALReader(logger log.Logger, w *WAL) *WALReader {
+	if logger == nil {
+		logger = log.NewNopLogger()
 	}
+	r := &WALReader{
+		logger: logger,
+		wal:    w,
+		buf:    make([]byte, 0, 128*4096),
+		crc32:  crc32.New(crc32.MakeTable(crc32.Castagnoli)),
+	}
+	return r
 }
 
 // At returns the last decoded entry of labels or samples.
@@ -446,19 +446,18 @@ func (r *WALReader) Err() error {
 
 // nextEntry retrieves the next entry. It is also used as a testing hook.
 func (r *WALReader) nextEntry() (WALEntryType, byte, []byte, error) {
-	if r.cur >= len(r.rs) {
+	if r.cur >= len(r.wal.files) {
 		return 0, 0, nil, io.EOF
 	}
-	cr := r.rs[r.cur]
+	cf := r.wal.files[r.cur]
 
-	et, flag, b, err := r.entry(cr)
+	et, flag, b, err := r.entry(cf)
 	// If we reached the end of the reader, advance to the next one
 	// and close.
 	// Do not close on the last one as it will still be appended to.
-	// XXX(fabxc): leaky abstraction.
-	if err == io.EOF && r.cur < len(r.rs)-1 {
+	if err == io.EOF && r.cur < len(r.wal.files)-1 {
 		// Current reader completed, close and move to the next one.
-		if err := cr.Close(); err != nil {
+		if err := cf.Close(); err != nil {
 			return 0, 0, nil, err
 		}
 		r.cur++
@@ -473,14 +472,46 @@ func (r *WALReader) Next() bool {
 	r.labels = r.labels[:0]
 	r.samples = r.samples[:0]
 
-	et, flag, b, err := r.nextEntry()
+	if r.cur >= len(r.wal.files) {
+		return false
+	}
+	cf := r.wal.files[r.cur]
+
+	// Save position after last valid entry if we have to truncate the WAL.
+	lastOffset, err := cf.Seek(0, os.SEEK_CUR)
 	if err != nil {
-		if err != io.EOF {
+		r.err = err
+		return false
+	}
+
+	et, flag, b, err := r.entry(cf)
+	// If we reached the end of the reader, advance to the next one
+	// and close.
+	// Do not close on the last one as it will still be appended to.
+	if err == io.EOF {
+		if r.cur == len(r.wal.files)-1 {
+			return false
+		}
+		// Current reader completed, close and move to the next one.
+		if err := cf.Close(); err != nil {
 			r.err = err
+			return false
+		}
+		r.cur++
+		return r.Next()
+	}
+	if err != nil {
+		r.err = err
+
+		if _, ok := err.(walCorruptionErr); ok {
+			r.err = r.truncate(lastOffset)
 		}
 		return false
 	}
 
+	// In decoding below we never return a walCorruptionErr for now.
+	// Those should generally be catched by entry decoding before.
+
 	switch et {
 	case WALEntrySamples:
 		if err := r.decodeSamples(flag, b); err != nil {
@@ -490,19 +521,52 @@ func (r *WALReader) Next() bool {
 		if err := r.decodeSeries(flag, b); err != nil {
 			r.err = err
 		}
-	default:
-		r.err = errors.Errorf("unknown WAL entry type %d", et)
 	}
 	return r.err == nil
 }
 
+func (r *WALReader) current() *os.File {
+	return r.wal.files[r.cur]
+}
+
+// truncate the WAL after the last valid entry.
+func (r *WALReader) truncate(lastOffset int64) error {
+	r.logger.Log("msg", "WAL corruption detected; truncating",
+		"err", r.err, "file", r.current().Name(), "pos", lastOffset)
+
+	// Close and delete all files after the current one.
+	for _, f := range r.wal.files[r.cur+1:] {
+		if err := f.Close(); err != nil {
+			return err
+		}
+		if err := os.Remove(f.Name()); err != nil {
+			return err
+		}
+	}
+	r.wal.files = r.wal.files[:r.cur+1]
+
+	// Seek the current file to the last valid offset where we continue writing from.
+	_, err := r.current().Seek(lastOffset, os.SEEK_SET)
+	return err
+}
+
+// walCorruptionErr is a type wrapper for errors that indicate WAL corruption
+// and trigger a truncation.
+type walCorruptionErr error
+
+func walCorruptionErrf(s string, args ...interface{}) error {
+	return walCorruptionErr(errors.Errorf(s, args...))
+}
+
 func (r *WALReader) entry(cr io.Reader) (WALEntryType, byte, []byte, error) {
 	r.crc32.Reset()
 	tr := io.TeeReader(cr, r.crc32)
 
 	b := make([]byte, 6)
-	if _, err := tr.Read(b); err != nil {
+	if n, err := tr.Read(b); err != nil {
 		return 0, 0, nil, err
+	} else if n != 6 {
+		return 0, 0, nil, walCorruptionErrf("invalid entry header size %d", n)
 	}
 
 	var (
@@ -514,21 +578,28 @@ func (r *WALReader) entry(cr io.Reader) (WALEntryType, byte, []byte, error) {
 	if etype == 0 {
 		return 0, 0, nil, io.EOF
 	}
+	if etype != WALEntrySeries && etype != WALEntrySamples {
+		return 0, 0, nil, walCorruptionErrf("invalid entry type %d", etype)
+	}
 
 	if length > len(r.buf) {
 		r.buf = make([]byte, length)
 	}
 	buf := r.buf[:length]
 
-	if _, err := tr.Read(buf); err != nil {
+	if n, err := tr.Read(buf); err != nil {
 		return 0, 0, nil, err
+	} else if n != length {
+		return 0, 0, nil, walCorruptionErrf("invalid entry body size %d", n)
 	}
-	_, err := cr.Read(b[:4])
-	if err != nil {
+
+	if n, err := cr.Read(b[:4]); err != nil {
 		return 0, 0, nil, err
+	} else if n != 4 {
+		return 0, 0, nil, walCorruptionErrf("invalid checksum length %d", n)
 	}
 	if exp, has := binary.BigEndian.Uint32(b[:4]), r.crc32.Sum32(); has != exp {
-		return 0, 0, nil, errors.Errorf("unexpected CRC32 checksum %x, want %x", has, exp)
+		return 0, 0, nil, walCorruptionErrf("unexpected CRC32 checksum %x, want %x", has, exp)
 	}
 
 	return etype, flag, buf, nil
diff --git a/vendor/vendor.json b/vendor/vendor.json
index 17eacc1da4..4d14b8af87 100644
--- a/vendor/vendor.json
+++ b/vendor/vendor.json
@@ -368,10 +368,10 @@
 			"revisionTime": "2016-09-30T00:14:02Z"
 		},
 		{
-			"checksumSHA1": "hnxY08GfzanNSvD8vjz/wSWnwmk=",
+			"checksumSHA1": "JeYYg27cZpCWZYwYOm7r+UnUR2o=",
 			"path": "github.com/fabxc/tsdb",
-			"revision": "32c32013a6d2a8ee5fb231d3f3cb5538128650d2",
-			"revisionTime": "2017-03-09T14:40:13Z"
+			"revision": "863d38dfeebaceb69ce57cbba862102e10222256",
+			"revisionTime": "2017-03-17T14:56:19Z"
 		},
 		{
 			"checksumSHA1": "uVzWuLvF646YjiKomsc2CR1ua58=",