diff --git a/storage/tsdb/tsdb.go b/storage/tsdb/tsdb.go
index 33572c93f..6be55c0c5 100644
--- a/storage/tsdb/tsdb.go
+++ b/storage/tsdb/tsdb.go
@@ -140,7 +140,11 @@ func Open(path string, l log.Logger, r prometheus.Registerer, opts *Options) (*t
 }
 
 func (a adapter) Querier(_ context.Context, mint, maxt int64) (storage.Querier, error) {
-	return querier{q: a.db.Querier(mint, maxt)}, nil
+	q, err := a.db.Querier(mint, maxt)
+	if err != nil {
+		return nil, err
+	}
+	return querier{q: q}, nil
 }
 
 // Appender returns a new appender against the storage.
diff --git a/vendor/github.com/prometheus/tsdb/block.go b/vendor/github.com/prometheus/tsdb/block.go
index 90915a1f0..63b468f27 100644
--- a/vendor/github.com/prometheus/tsdb/block.go
+++ b/vendor/github.com/prometheus/tsdb/block.go
@@ -19,6 +19,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"sync"
 
 	"github.com/oklog/ulid"
 	"github.com/pkg/errors"
@@ -26,33 +27,16 @@ import (
 	"github.com/prometheus/tsdb/labels"
 )
 
-// DiskBlock represents a data block backed by on-disk data.
-type DiskBlock interface {
-	BlockReader
-
-	// Directory where block data is stored.
-	Dir() string
-
-	// Stats returns statistics about the block.
-	Meta() BlockMeta
-
-	Delete(mint, maxt int64, m ...labels.Matcher) error
-
-	Snapshot(dir string) error
-
-	Close() error
-}
-
 // BlockReader provides reading access to a data block.
 type BlockReader interface {
 	// Index returns an IndexReader over the block's data.
-	Index() IndexReader
+	Index() (IndexReader, error)
 
 	// Chunks returns a ChunkReader over the block's data.
-	Chunks() ChunkReader
+	Chunks() (ChunkReader, error)
 
 	// Tombstones returns a TombstoneReader over the block's deleted data.
-	Tombstones() TombstoneReader
+	Tombstones() (TombstoneReader, error)
 }
 
 // Appendable defines an entity to which data can be appended.
@@ -149,7 +133,12 @@ func writeMetaFile(dir string, meta *BlockMeta) error {
 	return renameFile(tmp, path)
 }
 
-type persistedBlock struct {
+// Block represents a directory of time series data covering a continous time range.
+type Block struct {
+	mtx            sync.RWMutex
+	closing        bool
+	pendingReaders sync.WaitGroup
+
 	dir  string
 	meta BlockMeta
 
@@ -159,7 +148,9 @@ type persistedBlock struct {
 	tombstones tombstoneReader
 }
 
-func newPersistedBlock(dir string, pool chunks.Pool) (*persistedBlock, error) {
+// OpenBlock opens the block in the directory. It can be passed a chunk pool, which is used
+// to instantiate chunk structs.
+func OpenBlock(dir string, pool chunks.Pool) (*Block, error) {
 	meta, err := readMetaFile(dir)
 	if err != nil {
 		return nil, err
@@ -179,7 +170,7 @@ func newPersistedBlock(dir string, pool chunks.Pool) (*persistedBlock, error) {
 		return nil, err
 	}
 
-	pb := &persistedBlock{
+	pb := &Block{
 		dir:        dir,
 		meta:       *meta,
 		chunkr:     cr,
@@ -189,28 +180,110 @@ func newPersistedBlock(dir string, pool chunks.Pool) (*persistedBlock, error) {
 	return pb, nil
 }
 
-func (pb *persistedBlock) Close() error {
+// Close closes the on-disk block. It blocks as long as there are readers reading from the block.
+func (pb *Block) Close() error {
+	pb.mtx.Lock()
+	pb.closing = true
+	pb.mtx.Unlock()
+
+	pb.pendingReaders.Wait()
+
 	var merr MultiError
 
 	merr.Add(pb.chunkr.Close())
 	merr.Add(pb.indexr.Close())
+	merr.Add(pb.tombstones.Close())
 
 	return merr.Err()
 }
 
-func (pb *persistedBlock) String() string {
+func (pb *Block) String() string {
 	return pb.meta.ULID.String()
 }
 
-func (pb *persistedBlock) Dir() string         { return pb.dir }
-func (pb *persistedBlock) Index() IndexReader  { return pb.indexr }
-func (pb *persistedBlock) Chunks() ChunkReader { return pb.chunkr }
-func (pb *persistedBlock) Tombstones() TombstoneReader {
-	return pb.tombstones
-}
-func (pb *persistedBlock) Meta() BlockMeta { return pb.meta }
+// Dir returns the directory of the block.
+func (pb *Block) Dir() string { return pb.dir }
+
+// Meta returns meta information about the block.
+func (pb *Block) Meta() BlockMeta { return pb.meta }
+
+// ErrClosing is returned when a block is in the process of being closed.
+var ErrClosing = errors.New("block is closing")
+
+func (pb *Block) startRead() error {
+	pb.mtx.RLock()
+	defer pb.mtx.RUnlock()
+
+	if pb.closing {
+		return ErrClosing
+	}
+	pb.pendingReaders.Add(1)
+	return nil
+}
+
+// Index returns a new IndexReader against the block data.
+func (pb *Block) Index() (IndexReader, error) {
+	if err := pb.startRead(); err != nil {
+		return nil, err
+	}
+	return blockIndexReader{IndexReader: pb.indexr, b: pb}, nil
+}
+
+// Chunks returns a new ChunkReader against the block data.
+func (pb *Block) Chunks() (ChunkReader, error) {
+	if err := pb.startRead(); err != nil {
+		return nil, err
+	}
+	return blockChunkReader{ChunkReader: pb.chunkr, b: pb}, nil
+}
+
+// Tombstones returns a new TombstoneReader against the block data.
+func (pb *Block) Tombstones() (TombstoneReader, error) {
+	if err := pb.startRead(); err != nil {
+		return nil, err
+	}
+	return blockTombstoneReader{TombstoneReader: pb.tombstones, b: pb}, nil
+}
+
+type blockIndexReader struct {
+	IndexReader
+	b *Block
+}
+
+func (r blockIndexReader) Close() error {
+	r.b.pendingReaders.Done()
+	return nil
+}
+
+type blockTombstoneReader struct {
+	TombstoneReader
+	b *Block
+}
+
+func (r blockTombstoneReader) Close() error {
+	r.b.pendingReaders.Done()
+	return nil
+}
+
+type blockChunkReader struct {
+	ChunkReader
+	b *Block
+}
+
+func (r blockChunkReader) Close() error {
+	r.b.pendingReaders.Done()
+	return nil
+}
+
+// Delete matching series between mint and maxt in the block.
+func (pb *Block) Delete(mint, maxt int64, ms ...labels.Matcher) error {
+	pb.mtx.Lock()
+	defer pb.mtx.Unlock()
+
+	if pb.closing {
+		return ErrClosing
+	}
 
-func (pb *persistedBlock) Delete(mint, maxt int64, ms ...labels.Matcher) error {
 	pr := newPostingsReader(pb.indexr)
 	p, absent := pr.Select(ms...)
 
@@ -262,7 +335,8 @@ Outer:
 	return writeMetaFile(pb.dir, &pb.meta)
 }
 
-func (pb *persistedBlock) Snapshot(dir string) error {
+// Snapshot creates snapshot of the block into dir.
+func (pb *Block) Snapshot(dir string) error {
 	blockDir := filepath.Join(dir, pb.meta.ULID.String())
 	if err := os.MkdirAll(blockDir, 0777); err != nil {
 		return errors.Wrap(err, "create snapshot block dir")
@@ -311,7 +385,6 @@ func clampInterval(a, b, mint, maxt int64) (int64, int64) {
 	if b > maxt {
 		b = maxt
 	}
-
 	return a, b
 }
 
diff --git a/vendor/github.com/prometheus/tsdb/chunks.go b/vendor/github.com/prometheus/tsdb/chunks.go
index 626e7b41e..8152677f7 100644
--- a/vendor/github.com/prometheus/tsdb/chunks.go
+++ b/vendor/github.com/prometheus/tsdb/chunks.go
@@ -21,9 +21,9 @@ import (
 	"io"
 	"os"
 
-	"github.com/prometheus/tsdb/fileutil"
 	"github.com/pkg/errors"
 	"github.com/prometheus/tsdb/chunks"
+	"github.com/prometheus/tsdb/fileutil"
 )
 
 const (
diff --git a/vendor/github.com/prometheus/tsdb/compact.go b/vendor/github.com/prometheus/tsdb/compact.go
index 4f5c40e1a..5b66082aa 100644
--- a/vendor/github.com/prometheus/tsdb/compact.go
+++ b/vendor/github.com/prometheus/tsdb/compact.go
@@ -14,6 +14,7 @@
 package tsdb
 
 import (
+	"io"
 	"math/rand"
 	"os"
 	"path/filepath"
@@ -299,7 +300,7 @@ func (c *LeveledCompactor) Compact(dest string, dirs ...string) (err error) {
 	var metas []*BlockMeta
 
 	for _, d := range dirs {
-		b, err := newPersistedBlock(d, c.chunkPool)
+		b, err := OpenBlock(d, c.chunkPool)
 		if err != nil {
 			return err
 		}
@@ -444,10 +445,30 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 	var (
 		set        compactionSet
 		allSymbols = make(map[string]struct{}, 1<<16)
+		closers    = []io.Closer{}
 	)
-	for i, b := range blocks {
+	defer func() { closeAll(closers...) }()
 
-		symbols, err := b.Index().Symbols()
+	for i, b := range blocks {
+		indexr, err := b.Index()
+		if err != nil {
+			return errors.Wrapf(err, "open index reader for block %s", b)
+		}
+		closers = append(closers, indexr)
+
+		chunkr, err := b.Chunks()
+		if err != nil {
+			return errors.Wrapf(err, "open chunk reader for block %s", b)
+		}
+		closers = append(closers, chunkr)
+
+		tombsr, err := b.Tombstones()
+		if err != nil {
+			return errors.Wrapf(err, "open tombstone reader for block %s", b)
+		}
+		closers = append(closers, tombsr)
+
+		symbols, err := indexr.Symbols()
 		if err != nil {
 			return errors.Wrap(err, "read symbols")
 		}
@@ -455,15 +476,13 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 			allSymbols[s] = struct{}{}
 		}
 
-		indexr := b.Index()
-
 		all, err := indexr.Postings(allPostingsKey.Name, allPostingsKey.Value)
 		if err != nil {
 			return err
 		}
 		all = indexr.SortedPostings(all)
 
-		s := newCompactionSeriesSet(indexr, b.Chunks(), b.Tombstones(), all)
+		s := newCompactionSeriesSet(indexr, chunkr, tombsr, all)
 
 		if i == 0 {
 			set = s
@@ -565,7 +584,6 @@ func (c *LeveledCompactor) populateBlock(blocks []BlockReader, meta *BlockMeta,
 			return errors.Wrap(err, "write postings")
 		}
 	}
-
 	return nil
 }
 
diff --git a/vendor/github.com/prometheus/tsdb/db.go b/vendor/github.com/prometheus/tsdb/db.go
index e499de545..ff1763762 100644
--- a/vendor/github.com/prometheus/tsdb/db.go
+++ b/vendor/github.com/prometheus/tsdb/db.go
@@ -30,7 +30,6 @@ import (
 
 	"golang.org/x/sync/errgroup"
 
-	"github.com/prometheus/tsdb/fileutil"
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/nightlyone/lockfile"
@@ -38,6 +37,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/tsdb/chunks"
+	"github.com/prometheus/tsdb/fileutil"
 	"github.com/prometheus/tsdb/labels"
 )
 
@@ -105,7 +105,7 @@ type DB struct {
 
 	// Mutex for that must be held when modifying the general block layout.
 	mtx    sync.RWMutex
-	blocks []DiskBlock
+	blocks []*Block
 
 	head *Head
 
@@ -431,7 +431,7 @@ func retentionCutoff(dir string, mint int64) (bool, error) {
 	return changes, fileutil.Fsync(df)
 }
 
-func (db *DB) getBlock(id ulid.ULID) (DiskBlock, bool) {
+func (db *DB) getBlock(id ulid.ULID) (*Block, bool) {
 	for _, b := range db.blocks {
 		if b.Meta().ULID == id {
 			return b, true
@@ -456,7 +456,7 @@ func (db *DB) reload() (err error) {
 		return errors.Wrap(err, "find blocks")
 	}
 	var (
-		blocks []DiskBlock
+		blocks []*Block
 		exist  = map[ulid.ULID]struct{}{}
 	)
 
@@ -468,7 +468,7 @@ func (db *DB) reload() (err error) {
 
 		b, ok := db.getBlock(meta.ULID)
 		if !ok {
-			b, err = newPersistedBlock(dir, db.chunkPool)
+			b, err = OpenBlock(dir, db.chunkPool)
 			if err != nil {
 				return errors.Wrapf(err, "open block %s", dir)
 			}
@@ -505,7 +505,7 @@ func (db *DB) reload() (err error) {
 	return errors.Wrap(db.head.Truncate(maxt), "head truncate failed")
 }
 
-func validateBlockSequence(bs []DiskBlock) error {
+func validateBlockSequence(bs []*Block) error {
 	if len(bs) == 0 {
 		return nil
 	}
@@ -521,13 +521,19 @@ func validateBlockSequence(bs []DiskBlock) error {
 	return nil
 }
 
-func (db *DB) Blocks() []DiskBlock {
+func (db *DB) String() string {
+	return "HEAD"
+}
+
+// Blocks returns the databases persisted blocks.
+func (db *DB) Blocks() []*Block {
 	db.mtx.RLock()
 	defer db.mtx.RUnlock()
 
 	return db.blocks
 }
 
+// Head returns the databases's head.
 func (db *DB) Head() *Head {
 	return db.head
 }
@@ -587,41 +593,42 @@ func (db *DB) Snapshot(dir string) error {
 	db.cmtx.Lock()
 	defer db.cmtx.Unlock()
 
-	db.mtx.RLock()
-	defer db.mtx.RUnlock()
-
-	for _, b := range db.blocks {
+	for _, b := range db.Blocks() {
 		level.Info(db.logger).Log("msg", "snapshotting block", "block", b)
 
 		if err := b.Snapshot(dir); err != nil {
 			return errors.Wrap(err, "error snapshotting headblock")
 		}
 	}
-
 	return db.compactor.Write(dir, db.head, db.head.MinTime(), db.head.MaxTime())
 }
 
 // Querier returns a new querier over the data partition for the given time range.
 // A goroutine must not handle more than one open Querier.
-func (db *DB) Querier(mint, maxt int64) Querier {
-	db.mtx.RLock()
+func (db *DB) Querier(mint, maxt int64) (Querier, error) {
+	var blocks []BlockReader
 
-	blocks := db.blocksForInterval(mint, maxt)
+	for _, b := range db.Blocks() {
+		m := b.Meta()
+		if intervalOverlap(mint, maxt, m.MinTime, m.MaxTime) {
+			blocks = append(blocks, b)
+		}
+	}
+	if maxt >= db.head.MinTime() {
+		blocks = append(blocks, db.head)
+	}
 
 	sq := &querier{
 		blocks: make([]Querier, 0, len(blocks)),
-		db:     db,
 	}
 	for _, b := range blocks {
-		sq.blocks = append(sq.blocks, &blockQuerier{
-			mint:       mint,
-			maxt:       maxt,
-			index:      b.Index(),
-			chunks:     b.Chunks(),
-			tombstones: b.Tombstones(),
-		})
+		q, err := NewBlockQuerier(b, mint, maxt)
+		if err != nil {
+			return nil, errors.Wrapf(err, "open querier for block %s", b)
+		}
+		sq.blocks = append(sq.blocks, q)
 	}
-	return sq
+	return sq, nil
 }
 
 func rangeForTimestamp(t int64, width int64) (mint, maxt int64) {
@@ -634,28 +641,22 @@ func (db *DB) Delete(mint, maxt int64, ms ...labels.Matcher) error {
 	db.cmtx.Lock()
 	defer db.cmtx.Unlock()
 
-	db.mtx.Lock()
-	defer db.mtx.Unlock()
-
 	var g errgroup.Group
 
-	for _, b := range db.blocks {
+	for _, b := range db.Blocks() {
 		m := b.Meta()
 		if intervalOverlap(mint, maxt, m.MinTime, m.MaxTime) {
-			g.Go(func(b DiskBlock) func() error {
+			g.Go(func(b *Block) func() error {
 				return func() error { return b.Delete(mint, maxt, ms...) }
 			}(b))
 		}
 	}
-
 	g.Go(func() error {
 		return db.head.Delete(mint, maxt, ms...)
 	})
-
 	if err := g.Wait(); err != nil {
 		return err
 	}
-
 	return nil
 }
 
@@ -668,24 +669,6 @@ func intervalContains(min, max, t int64) bool {
 	return t >= min && t <= max
 }
 
-// blocksForInterval returns all blocks within the partition that may contain
-// data for the given time range.
-func (db *DB) blocksForInterval(mint, maxt int64) []BlockReader {
-	var bs []BlockReader
-
-	for _, b := range db.blocks {
-		m := b.Meta()
-		if intervalOverlap(mint, maxt, m.MinTime, m.MaxTime) {
-			bs = append(bs, b)
-		}
-	}
-	if maxt >= db.head.MinTime() {
-		bs = append(bs, db.head)
-	}
-
-	return bs
-}
-
 func isBlockDir(fi os.FileInfo) bool {
 	if !fi.IsDir() {
 		return false
diff --git a/vendor/github.com/prometheus/tsdb/head.go b/vendor/github.com/prometheus/tsdb/head.go
index 82a3459bd..37126363d 100644
--- a/vendor/github.com/prometheus/tsdb/head.go
+++ b/vendor/github.com/prometheus/tsdb/head.go
@@ -15,6 +15,7 @@ package tsdb
 
 import (
 	"math"
+	"runtime"
 	"sort"
 	"sync"
 	"sync/atomic"
@@ -73,6 +74,7 @@ type headMetrics struct {
 	series              prometheus.Gauge
 	seriesCreated       prometheus.Counter
 	seriesRemoved       prometheus.Counter
+	seriesNotFound      prometheus.Counter
 	chunks              prometheus.Gauge
 	chunksCreated       prometheus.Gauge
 	chunksRemoved       prometheus.Gauge
@@ -102,6 +104,10 @@ func newHeadMetrics(h *Head, r prometheus.Registerer) *headMetrics {
 		Name: "tsdb_head_series_removed_total",
 		Help: "Total number of series removed in the head",
 	})
+	m.seriesNotFound = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "tsdb_head_series_not_found",
+		Help: "Total number of requests for series that were not found.",
+	})
 	m.chunks = prometheus.NewGauge(prometheus.GaugeOpts{
 		Name: "tsdb_head_chunks",
 		Help: "Total number of chunks in the head block.",
@@ -118,13 +124,13 @@ func newHeadMetrics(h *Head, r prometheus.Registerer) *headMetrics {
 		Name: "tsdb_head_gc_duration_seconds",
 		Help: "Runtime of garbage collection in the head block.",
 	})
-	m.minTime = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+	m.maxTime = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
 		Name: "tsdb_head_max_time",
 		Help: "Maximum timestamp of the head block.",
 	}, func() float64 {
 		return float64(h.MaxTime())
 	})
-	m.maxTime = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
+	m.minTime = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
 		Name: "tsdb_head_min_time",
 		Help: "Minimum time bound of the head block.",
 	}, func() float64 {
@@ -148,6 +154,7 @@ func newHeadMetrics(h *Head, r prometheus.Registerer) *headMetrics {
 			m.series,
 			m.seriesCreated,
 			m.seriesRemoved,
+			m.seriesNotFound,
 			m.minTime,
 			m.maxTime,
 			m.gcDuration,
@@ -178,7 +185,7 @@ func NewHead(r prometheus.Registerer, l log.Logger, wal WAL, chunkRange int64) (
 		series:     newStripeSeries(),
 		values:     map[string]stringset{},
 		symbols:    map[string]struct{}{},
-		postings:   newMemPostings(),
+		postings:   newUnorderedMemPostings(),
 		tombstones: newEmptyTombstoneReader(),
 	}
 	h.metrics = newHeadMetrics(h, r)
@@ -186,28 +193,19 @@ func NewHead(r prometheus.Registerer, l log.Logger, wal WAL, chunkRange int64) (
 	return h, nil
 }
 
-// ReadWAL initializes the head by consuming the write ahead log.
-func (h *Head) ReadWAL() error {
-	r := h.wal.Reader()
-	mint := h.MinTime()
+// processWALSamples adds a partition of samples it receives to the head and passes
+// them on to other workers.
+// Samples before the mint timestamp are discarded.
+func (h *Head) processWALSamples(
+	mint int64,
+	partition, total uint64,
+	input <-chan []RefSample, output chan<- []RefSample,
+) (unknownRefs uint64) {
+	defer close(output)
 
-	// Track number of samples that referenced a series we don't know about
-	// for error reporting.
-	var unknownRefs int
-
-	seriesFunc := func(series []RefSeries) error {
-		for _, s := range series {
-			h.getOrCreateWithID(s.Ref, s.Labels.Hash(), s.Labels)
-
-			if h.lastSeriesID < s.Ref {
-				h.lastSeriesID = s.Ref
-			}
-		}
-		return nil
-	}
-	samplesFunc := func(samples []RefSample) error {
+	for samples := range input {
 		for _, s := range samples {
-			if s.T < mint {
+			if s.T < mint || s.Ref%total != partition {
 				continue
 			}
 			ms := h.series.getByID(s.Ref)
@@ -221,9 +219,69 @@ func (h *Head) ReadWAL() error {
 				h.metrics.chunks.Inc()
 			}
 		}
-		return nil
+		output <- samples
 	}
-	deletesFunc := func(stones []Stone) error {
+	return unknownRefs
+}
+
+// ReadWAL initializes the head by consuming the write ahead log.
+func (h *Head) ReadWAL() error {
+	defer h.postings.ensureOrder()
+
+	r := h.wal.Reader()
+	mint := h.MinTime()
+
+	// Track number of samples that referenced a series we don't know about
+	// for error reporting.
+	var unknownRefs uint64
+
+	// Start workers that each process samples for a partition of the series ID space.
+	// They are connected through a ring of channels which ensures that all sample batches
+	// read from the WAL are processed in order.
+	var (
+		wg         sync.WaitGroup
+		n          = runtime.GOMAXPROCS(0)
+		firstInput = make(chan []RefSample, 300)
+		input      = firstInput
+	)
+	wg.Add(n)
+
+	for i := 0; i < n; i++ {
+		output := make(chan []RefSample, 300)
+
+		go func(i int, input <-chan []RefSample, output chan<- []RefSample) {
+			unknown := h.processWALSamples(mint, uint64(i), uint64(n), input, output)
+			atomic.AddUint64(&unknownRefs, unknown)
+			wg.Done()
+		}(i, input, output)
+
+		// The output feeds the next worker goroutine. For the last worker,
+		// it feeds the initial input again to reuse the RefSample slices.
+		input = output
+	}
+
+	// TODO(fabxc): series entries spread between samples can starve the sample workers.
+	// Even with bufferd channels, this can impact startup time with lots of series churn.
+	// We must not pralellize series creation itself but could make the indexing asynchronous.
+	seriesFunc := func(series []RefSeries) {
+		for _, s := range series {
+			h.getOrCreateWithID(s.Ref, s.Labels.Hash(), s.Labels)
+
+			if h.lastSeriesID < s.Ref {
+				h.lastSeriesID = s.Ref
+			}
+		}
+	}
+	samplesFunc := func(samples []RefSample) {
+		var buf []RefSample
+		select {
+		case buf = <-input:
+		default:
+			buf = make([]RefSample, 0, len(samples)*11/10)
+		}
+		firstInput <- append(buf[:0], samples...)
+	}
+	deletesFunc := func(stones []Stone) {
 		for _, s := range stones {
 			for _, itv := range s.intervals {
 				if itv.Maxt < mint {
@@ -232,16 +290,22 @@ func (h *Head) ReadWAL() error {
 				h.tombstones.add(s.ref, itv)
 			}
 		}
-		return nil
 	}
 
+	err := r.Read(seriesFunc, samplesFunc, deletesFunc)
+
+	// Signal termination to first worker and wait for last one to close its output channel.
+	close(firstInput)
+	for range input {
+	}
+	wg.Wait()
+
+	if err != nil {
+		return errors.Wrap(err, "consume WAL")
+	}
 	if unknownRefs > 0 {
 		level.Warn(h.logger).Log("msg", "unknown series references in WAL samples", "count", unknownRefs)
 	}
-
-	if err := r.Read(seriesFunc, samplesFunc, deletesFunc); err != nil {
-		return errors.Wrap(err, "consume WAL")
-	}
 	return nil
 }
 
@@ -303,6 +367,23 @@ func (h *Head) initTime(t int64) (initialized bool) {
 	return true
 }
 
+type rangeHead struct {
+	head       *Head
+	mint, maxt int64
+}
+
+func (h *rangeHead) Index() (IndexReader, error) {
+	return h.head.indexRange(h.mint, h.maxt), nil
+}
+
+func (h *rangeHead) Chunks() (ChunkReader, error) {
+	return h.head.chunksRange(h.mint, h.maxt), nil
+}
+
+func (h *rangeHead) Tombstones() (TombstoneReader, error) {
+	return h.head.tombstones, nil
+}
+
 // initAppender is a helper to initialize the time bounds of a the head
 // upon the first sample it receives.
 type initAppender struct {
@@ -609,13 +690,14 @@ func (h *Head) gc() {
 	h.symMtx.Unlock()
 }
 
-func (h *Head) Tombstones() TombstoneReader {
-	return h.tombstones
+// Tombstones returns a new reader over the head's tombstones
+func (h *Head) Tombstones() (TombstoneReader, error) {
+	return h.tombstones, nil
 }
 
 // Index returns an IndexReader against the block.
-func (h *Head) Index() IndexReader {
-	return h.indexRange(math.MinInt64, math.MaxInt64)
+func (h *Head) Index() (IndexReader, error) {
+	return h.indexRange(math.MinInt64, math.MaxInt64), nil
 }
 
 func (h *Head) indexRange(mint, maxt int64) *headIndexReader {
@@ -626,8 +708,8 @@ func (h *Head) indexRange(mint, maxt int64) *headIndexReader {
 }
 
 // Chunks returns a ChunkReader against the block.
-func (h *Head) Chunks() ChunkReader {
-	return h.chunksRange(math.MinInt64, math.MaxInt64)
+func (h *Head) Chunks() (ChunkReader, error) {
+	return h.chunksRange(math.MinInt64, math.MaxInt64), nil
 }
 
 func (h *Head) chunksRange(mint, maxt int64) *headChunkReader {
@@ -680,10 +762,11 @@ func (h *headChunkReader) Chunk(ref uint64) (chunks.Chunk, error) {
 
 	s.Lock()
 	c := s.chunk(int(cid))
+	mint, maxt := c.minTime, c.maxTime
 	s.Unlock()
 
 	// Do not expose chunks that are outside of the specified range.
-	if c == nil || !intervalOverlap(c.minTime, c.maxTime, h.mint, h.maxt) {
+	if c == nil || !intervalOverlap(mint, maxt, h.mint, h.maxt) {
 		return nil, ErrNotFound
 	}
 	return &safeChunk{
@@ -710,23 +793,6 @@ func (c *safeChunk) Iterator() chunks.Iterator {
 // func (c *safeChunk) Bytes() []byte                      { panic("illegal") }
 // func (c *safeChunk) Encoding() chunks.Encoding          { panic("illegal") }
 
-type rangeHead struct {
-	head       *Head
-	mint, maxt int64
-}
-
-func (h *rangeHead) Index() IndexReader {
-	return h.head.indexRange(h.mint, h.maxt)
-}
-
-func (h *rangeHead) Chunks() ChunkReader {
-	return h.head.chunksRange(h.mint, h.maxt)
-}
-
-func (h *rangeHead) Tombstones() TombstoneReader {
-	return newEmptyTombstoneReader()
-}
-
 type headIndexReader struct {
 	head       *Head
 	mint, maxt int64
@@ -780,24 +846,17 @@ func (h *headIndexReader) SortedPostings(p Postings) Postings {
 	if err := p.Err(); err != nil {
 		return errPostings{err: errors.Wrap(err, "expand postings")}
 	}
-	var err error
 
 	sort.Slice(ep, func(i, j int) bool {
-		if err != nil {
-			return false
-		}
 		a := h.head.series.getByID(ep[i])
 		b := h.head.series.getByID(ep[j])
 
 		if a == nil || b == nil {
-			err = errors.Errorf("series not found")
+			level.Debug(h.head.logger).Log("msg", "looked up series not found")
 			return false
 		}
 		return labels.Compare(a.lset, b.lset) < 0
 	})
-	if err != nil {
-		return errPostings{err: err}
-	}
 	return newListPostings(ep)
 }
 
@@ -806,6 +865,7 @@ func (h *headIndexReader) Series(ref uint64, lbls *labels.Labels, chks *[]ChunkM
 	s := h.head.series.getByID(ref)
 
 	if s == nil {
+		h.head.metrics.seriesNotFound.Inc()
 		return ErrNotFound
 	}
 	*lbls = append((*lbls)[:0], s.lset...)
@@ -1169,10 +1229,12 @@ func (s *memSeries) append(t int64, v float64) (success, chunkCreated bool) {
 		c = s.cut(t)
 		chunkCreated = true
 	}
+	numSamples := c.chunk.NumSamples()
+
 	if c.maxTime >= t {
 		return false, chunkCreated
 	}
-	if c.chunk.NumSamples() > samplesPerChunk/4 && t >= s.nextAt {
+	if numSamples > samplesPerChunk/4 && t >= s.nextAt {
 		c = s.cut(t)
 		chunkCreated = true
 	}
@@ -1180,7 +1242,7 @@ func (s *memSeries) append(t int64, v float64) (success, chunkCreated bool) {
 
 	c.maxTime = t
 
-	if c.chunk.NumSamples() == samplesPerChunk/4 {
+	if numSamples == samplesPerChunk/4 {
 		_, maxt := rangeForTimestamp(c.minTime, s.chunkRange)
 		s.nextAt = computeChunkEndTime(c.minTime, c.maxTime, maxt)
 	}
diff --git a/vendor/github.com/prometheus/tsdb/index.go b/vendor/github.com/prometheus/tsdb/index.go
index b9cda3073..c0680aa33 100644
--- a/vendor/github.com/prometheus/tsdb/index.go
+++ b/vendor/github.com/prometheus/tsdb/index.go
@@ -19,14 +19,14 @@ import (
 	"fmt"
 	"hash"
 	"io"
+	"math"
 	"os"
 	"path/filepath"
 	"sort"
 	"strings"
-	"math"
 
-	"github.com/prometheus/tsdb/fileutil"
 	"github.com/pkg/errors"
+	"github.com/prometheus/tsdb/fileutil"
 	"github.com/prometheus/tsdb/labels"
 )
 
@@ -525,6 +525,8 @@ type IndexReader interface {
 
 	// Postings returns the postings list iterator for the label pair.
 	// The Postings here contain the offsets to the series inside the index.
+	// Found IDs are not strictly required to point to a valid Series, e.g. during
+	// background garbage collections.
 	Postings(name, value string) (Postings, error)
 
 	// SortedPostings returns a postings list that is reordered to be sorted
@@ -533,6 +535,7 @@ type IndexReader interface {
 
 	// Series populates the given labels and chunk metas for the series identified
 	// by the reference.
+	// Returns ErrNotFound if the ref does not resolve to a known series.
 	Series(ref uint64, lset *labels.Labels, chks *[]ChunkMeta) error
 
 	// LabelIndices returns the label pairs for which indices exist.
diff --git a/vendor/github.com/prometheus/tsdb/postings.go b/vendor/github.com/prometheus/tsdb/postings.go
index 0e51b221b..2647f4dd8 100644
--- a/vendor/github.com/prometheus/tsdb/postings.go
+++ b/vendor/github.com/prometheus/tsdb/postings.go
@@ -15,6 +15,7 @@ package tsdb
 
 import (
 	"encoding/binary"
+	"runtime"
 	"sort"
 	"strings"
 	"sync"
@@ -22,14 +23,30 @@ import (
 	"github.com/prometheus/tsdb/labels"
 )
 
+// memPostings holds postings list for series ID per label pair. They may be written
+// to out of order.
+// ensureOrder() must be called once before any reads are done. This allows for quick
+// unordered batch fills on startup.
 type memPostings struct {
-	mtx sync.RWMutex
-	m   map[labels.Label][]uint64
+	mtx     sync.RWMutex
+	m       map[labels.Label][]uint64
+	ordered bool
 }
 
+// newMemPoistings returns a memPostings that's ready for reads and writes.
 func newMemPostings() *memPostings {
 	return &memPostings{
-		m: make(map[labels.Label][]uint64, 512),
+		m:       make(map[labels.Label][]uint64, 512),
+		ordered: true,
+	}
+}
+
+// newUnorderedMemPostings returns a memPostings that is not safe to be read from
+// until ensureOrder was called once.
+func newUnorderedMemPostings() *memPostings {
+	return &memPostings{
+		m:       make(map[labels.Label][]uint64, 512),
+		ordered: false,
 	}
 }
 
@@ -47,6 +64,40 @@ func (p *memPostings) get(name, value string) Postings {
 
 var allPostingsKey = labels.Label{}
 
+// ensurePostings ensures that all postings lists are sorted. After it returns all further
+// calls to add and addFor will insert new IDs in a sorted manner.
+func (p *memPostings) ensureOrder() {
+	p.mtx.Lock()
+	defer p.mtx.Unlock()
+
+	if p.ordered {
+		return
+	}
+
+	n := runtime.GOMAXPROCS(0)
+	workc := make(chan []uint64)
+
+	var wg sync.WaitGroup
+	wg.Add(n)
+
+	for i := 0; i < n; i++ {
+		go func() {
+			for l := range workc {
+				sort.Slice(l, func(i, j int) bool { return l[i] < l[j] })
+			}
+			wg.Done()
+		}()
+	}
+
+	for _, l := range p.m {
+		workc <- l
+	}
+	close(workc)
+	wg.Wait()
+
+	p.ordered = true
+}
+
 // add adds a document to the index. The caller has to ensure that no
 // term argument appears twice.
 func (p *memPostings) add(id uint64, lset labels.Labels) {
@@ -64,6 +115,9 @@ func (p *memPostings) addFor(id uint64, l labels.Label) {
 	list := append(p.m[l], id)
 	p.m[l] = list
 
+	if !p.ordered {
+		return
+	}
 	// There is no guarantee that no higher ID was inserted before as they may
 	// be generated independently before adding them to postings.
 	// We repair order violations on insert. The invariant is that the first n-1
diff --git a/vendor/github.com/prometheus/tsdb/querier.go b/vendor/github.com/prometheus/tsdb/querier.go
index 5461fec89..12e05e79d 100644
--- a/vendor/github.com/prometheus/tsdb/querier.go
+++ b/vendor/github.com/prometheus/tsdb/querier.go
@@ -18,6 +18,7 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/pkg/errors"
 	"github.com/prometheus/tsdb/chunks"
 	"github.com/prometheus/tsdb/labels"
 )
@@ -50,7 +51,6 @@ type Series interface {
 // querier aggregates querying results from time blocks within
 // a single partition.
 type querier struct {
-	db     *DB
 	blocks []Querier
 }
 
@@ -103,21 +103,30 @@ func (q *querier) Close() error {
 	for _, bq := range q.blocks {
 		merr.Add(bq.Close())
 	}
-	q.db.mtx.RUnlock()
-
 	return merr.Err()
 }
 
 // NewBlockQuerier returns a queries against the readers.
-func NewBlockQuerier(ir IndexReader, cr ChunkReader, tr TombstoneReader, mint, maxt int64) Querier {
-	return &blockQuerier{
-		index:      ir,
-		chunks:     cr,
-		tombstones: tr,
-
-		mint: mint,
-		maxt: maxt,
+func NewBlockQuerier(b BlockReader, mint, maxt int64) (Querier, error) {
+	indexr, err := b.Index()
+	if err != nil {
+		return nil, errors.Wrapf(err, "open index reader")
 	}
+	chunkr, err := b.Chunks()
+	if err != nil {
+		return nil, errors.Wrapf(err, "open chunk reader")
+	}
+	tombsr, err := b.Tombstones()
+	if err != nil {
+		return nil, errors.Wrapf(err, "open tombstone reader")
+	}
+	return &blockQuerier{
+		mint:       mint,
+		maxt:       maxt,
+		index:      indexr,
+		chunks:     chunkr,
+		tombstones: tombsr,
+	}, nil
 }
 
 // blockQuerier provides querying access to a single block database.
@@ -175,7 +184,13 @@ func (q *blockQuerier) LabelValuesFor(string, labels.Label) ([]string, error) {
 }
 
 func (q *blockQuerier) Close() error {
-	return nil
+	var merr MultiError
+
+	merr.Add(q.index.Close())
+	merr.Add(q.chunks.Close())
+	merr.Add(q.tombstones.Close())
+
+	return merr.Err()
 }
 
 // postingsReader is used to select matching postings from an IndexReader.
@@ -435,6 +450,10 @@ Outer:
 	for s.p.Next() {
 		ref := s.p.At()
 		if err := s.index.Series(ref, &lset, &chunks); err != nil {
+			// Postings may be stale. Skip if no underlying series exists.
+			if errors.Cause(err) == ErrNotFound {
+				continue
+			}
 			s.err = err
 			return false
 		}
diff --git a/vendor/github.com/prometheus/tsdb/tabwriter.go b/vendor/github.com/prometheus/tsdb/tabwriter.go
new file mode 100644
index 000000000..8e84a9c67
--- /dev/null
+++ b/vendor/github.com/prometheus/tsdb/tabwriter.go
@@ -0,0 +1,18 @@
+package tsdb
+
+import (
+	"io"
+	"text/tabwriter"
+)
+
+const (
+	minwidth = 0
+	tabwidth = 0
+	padding  = 2
+	padchar  = ' '
+	flags    = 0
+)
+
+func GetNewTabWriter(output io.Writer) *tabwriter.Writer {
+	return tabwriter.NewWriter(output, minwidth, tabwidth, padding, padchar, flags)
+}
diff --git a/vendor/github.com/prometheus/tsdb/tombstones.go b/vendor/github.com/prometheus/tsdb/tombstones.go
index 7b24407b5..19b224634 100644
--- a/vendor/github.com/prometheus/tsdb/tombstones.go
+++ b/vendor/github.com/prometheus/tsdb/tombstones.go
@@ -33,9 +33,11 @@ const (
 	tombstoneFormatV1 = 1
 )
 
-// TombstoneReader is the iterator over tombstones.
+// TombstoneReader gives access to tombstone intervals by series reference.
 type TombstoneReader interface {
 	Get(ref uint64) Intervals
+
+	Close() error
 }
 
 func writeTombstoneFile(dir string, tr tombstoneReader) error {
@@ -154,6 +156,10 @@ func (t tombstoneReader) add(ref uint64, itv Interval) {
 	t[ref] = t[ref].add(itv)
 }
 
+func (tombstoneReader) Close() error {
+	return nil
+}
+
 // Interval represents a single time-interval.
 type Interval struct {
 	Mint, Maxt int64
diff --git a/vendor/github.com/prometheus/tsdb/wal.go b/vendor/github.com/prometheus/tsdb/wal.go
index 467c4e09b..5c6e78d2e 100644
--- a/vendor/github.com/prometheus/tsdb/wal.go
+++ b/vendor/github.com/prometheus/tsdb/wal.go
@@ -27,16 +27,16 @@ import (
 	"sync"
 	"time"
 
-	"github.com/prometheus/tsdb/fileutil"
 	"github.com/go-kit/kit/log"
 	"github.com/go-kit/kit/log/level"
 	"github.com/pkg/errors"
-	"github.com/prometheus/tsdb/labels"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/tsdb/fileutil"
+	"github.com/prometheus/tsdb/labels"
 )
 
 // WALEntryType indicates what data a WAL entry contains.
-type WALEntryType byte
+type WALEntryType uint8
 
 const (
 	// WALMagic is a 4 byte number every WAL segment file starts with.
@@ -54,20 +54,9 @@ const (
 	WALEntryDeletes WALEntryType = 4
 )
 
-// SamplesCB is the callback after reading samples. The passed slice
-// is only valid until the call returns.
-type SamplesCB func([]RefSample) error
-
-// SeriesCB is the callback after reading series. The passed slice
-// is only valid until the call returns.
-type SeriesCB func([]RefSeries) error
-
-// DeletesCB is the callback after reading deletes. The passed slice
-// is only valid until the call returns.
-type DeletesCB func([]Stone) error
-
 type walMetrics struct {
 	fsyncDuration prometheus.Summary
+	corruptions   prometheus.Counter
 }
 
 func newWalMetrics(wal *SegmentWAL, r prometheus.Registerer) *walMetrics {
@@ -77,10 +66,15 @@ func newWalMetrics(wal *SegmentWAL, r prometheus.Registerer) *walMetrics {
 		Name: "tsdb_wal_fsync_duration_seconds",
 		Help: "Duration of WAL fsync.",
 	})
+	m.corruptions = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "tsdb_wal_corruptions_total",
+		Help: "Total number of WAL corruptions.",
+	})
 
 	if r != nil {
 		r.MustRegister(
 			m.fsyncDuration,
+			m.corruptions,
 		)
 	}
 	return m
@@ -104,17 +98,27 @@ func NopWAL() WAL {
 
 type nopWAL struct{}
 
-func (nopWAL) Read(SeriesCB, SamplesCB, DeletesCB) error { return nil }
-func (w nopWAL) Reader() WALReader                       { return w }
-func (nopWAL) LogSeries([]RefSeries) error               { return nil }
-func (nopWAL) LogSamples([]RefSample) error              { return nil }
-func (nopWAL) LogDeletes([]Stone) error                  { return nil }
-func (nopWAL) Truncate(int64, func(uint64) bool) error   { return nil }
-func (nopWAL) Close() error                              { return nil }
+func (nopWAL) Read(
+	seriesf func([]RefSeries),
+	samplesf func([]RefSample),
+	deletesf func([]Stone),
+) error {
+	return nil
+}
+func (w nopWAL) Reader() WALReader                     { return w }
+func (nopWAL) LogSeries([]RefSeries) error             { return nil }
+func (nopWAL) LogSamples([]RefSample) error            { return nil }
+func (nopWAL) LogDeletes([]Stone) error                { return nil }
+func (nopWAL) Truncate(int64, func(uint64) bool) error { return nil }
+func (nopWAL) Close() error                            { return nil }
 
 // WALReader reads entries from a WAL.
 type WALReader interface {
-	Read(SeriesCB, SamplesCB, DeletesCB) error
+	Read(
+		seriesf func([]RefSeries),
+		samplesf func([]RefSample),
+		deletesf func([]Stone),
+	) error
 }
 
 // RefSeries is the series labels with the series ID.
@@ -170,7 +174,7 @@ func newCRC32() hash.Hash32 {
 
 // SegmentWAL is a write ahead log for series data.
 type SegmentWAL struct {
-	mtx sync.Mutex
+	mtx     sync.Mutex
 	metrics *walMetrics
 
 	dirFile *os.File
@@ -238,15 +242,20 @@ type repairingWALReader struct {
 	r   WALReader
 }
 
-func (r *repairingWALReader) Read(series SeriesCB, samples SamplesCB, deletes DeletesCB) error {
-	err := r.r.Read(series, samples, deletes)
+func (r *repairingWALReader) Read(
+	seriesf func([]RefSeries),
+	samplesf func([]RefSample),
+	deletesf func([]Stone),
+) error {
+	err := r.r.Read(seriesf, samplesf, deletesf)
 	if err == nil {
 		return nil
 	}
-	cerr, ok := err.(walCorruptionErr)
+	cerr, ok := errors.Cause(err).(walCorruptionErr)
 	if !ok {
 		return err
 	}
+	r.wal.metrics.corruptions.Inc()
 	return r.wal.truncate(cerr.err, cerr.file, cerr.lastOffset)
 }
 
@@ -336,6 +345,7 @@ func (w *SegmentWAL) Truncate(mint int64, keep func(uint64) bool) error {
 	var (
 		csf          = newSegmentFile(f)
 		crc32        = newCRC32()
+		decSeries    = []RefSeries{}
 		activeSeries = []RefSeries{}
 	)
 
@@ -345,13 +355,14 @@ func (w *SegmentWAL) Truncate(mint int64, keep func(uint64) bool) error {
 		if rt != WALEntrySeries {
 			continue
 		}
-		series, err := r.decodeSeries(flag, byt)
+		decSeries = decSeries[:0]
+		activeSeries = activeSeries[:0]
+
+		err := r.decodeSeries(flag, byt, &decSeries)
 		if err != nil {
 			return errors.Wrap(err, "decode samples while truncating")
 		}
-		activeSeries = activeSeries[:0]
-
-		for _, s := range series {
+		for _, s := range decSeries {
 			if keep(s.Ref) {
 				activeSeries = append(activeSeries, s)
 			}
@@ -807,10 +818,6 @@ type walReader struct {
 	curBuf     []byte
 	lastOffset int64 // offset after last successfully read entry
 
-	seriesBuf    []RefSeries
-	sampleBuf    []RefSample
-	tombstoneBuf []Stone
-
 	err error
 }
 
@@ -831,70 +838,118 @@ func (r *walReader) Err() error {
 	return r.err
 }
 
-func (r *walReader) Read(seriesf SeriesCB, samplesf SamplesCB, deletesf DeletesCB) error {
-	if seriesf == nil {
-		seriesf = func([]RefSeries) error { return nil }
-	}
-	if samplesf == nil {
-		samplesf = func([]RefSample) error { return nil }
-	}
-	if deletesf == nil {
-		deletesf = func([]Stone) error { return nil }
-	}
+func (r *walReader) Read(
+	seriesf func([]RefSeries),
+	samplesf func([]RefSample),
+	deletesf func([]Stone),
+) error {
+	// Concurrency for replaying the WAL is very limited. We at least split out decoding and
+	// processing into separate threads.
+	// Historically, the processing is the bottleneck with reading and decoding using only
+	// 15% of the CPU.
+	var (
+		seriesPool sync.Pool
+		samplePool sync.Pool
+		deletePool sync.Pool
+	)
+	donec := make(chan struct{})
+	datac := make(chan interface{}, 100)
+
+	go func() {
+		defer close(donec)
+
+		for x := range datac {
+			switch v := x.(type) {
+			case []RefSeries:
+				if seriesf != nil {
+					seriesf(v)
+				}
+				seriesPool.Put(v[:0])
+			case []RefSample:
+				if samplesf != nil {
+					samplesf(v)
+				}
+				samplePool.Put(v[:0])
+			case []Stone:
+				if deletesf != nil {
+					deletesf(v)
+				}
+				deletePool.Put(v[:0])
+			default:
+				level.Error(r.logger).Log("msg", "unexpected data type")
+			}
+		}
+	}()
+
+	var err error
 
 	for r.next() {
 		et, flag, b := r.at()
+
 		// In decoding below we never return a walCorruptionErr for now.
 		// Those should generally be catched by entry decoding before.
 		switch et {
 		case WALEntrySeries:
-			series, err := r.decodeSeries(flag, b)
+			var series []RefSeries
+			if v := seriesPool.Get(); v == nil {
+				series = make([]RefSeries, 0, 512)
+			} else {
+				series = v.([]RefSeries)
+			}
+
+			err := r.decodeSeries(flag, b, &series)
 			if err != nil {
-				return errors.Wrap(err, "decode series entry")
-			}
-			if err := seriesf(series); err != nil {
-				return err
+				err = errors.Wrap(err, "decode series entry")
+				break
 			}
+			datac <- series
 
 			cf := r.current()
-
 			for _, s := range series {
 				if cf.minSeries > s.Ref {
 					cf.minSeries = s.Ref
 				}
 			}
-
 		case WALEntrySamples:
-			samples, err := r.decodeSamples(flag, b)
+			var samples []RefSample
+			if v := samplePool.Get(); v == nil {
+				samples = make([]RefSample, 0, 512)
+			} else {
+				samples = v.([]RefSample)
+			}
+
+			err := r.decodeSamples(flag, b, &samples)
 			if err != nil {
-				return errors.Wrap(err, "decode samples entry")
-			}
-			if err := samplesf(samples); err != nil {
-				return err
+				err = errors.Wrap(err, "decode samples entry")
+				break
 			}
+			datac <- samples
 
 			// Update the times for the WAL segment file.
 			cf := r.current()
-
 			for _, s := range samples {
 				if cf.maxTime < s.T {
 					cf.maxTime = s.T
 				}
 			}
-
 		case WALEntryDeletes:
-			stones, err := r.decodeDeletes(flag, b)
+			var deletes []Stone
+			if v := deletePool.Get(); v == nil {
+				deletes = make([]Stone, 0, 512)
+			} else {
+				deletes = v.([]Stone)
+			}
+
+			err := r.decodeDeletes(flag, b, &deletes)
 			if err != nil {
-				return errors.Wrap(err, "decode delete entry")
-			}
-			if err := deletesf(stones); err != nil {
-				return err
+				err = errors.Wrap(err, "decode delete entry")
+				break
 			}
+			datac <- deletes
+
 			// Update the times for the WAL segment file.
-
 			cf := r.current()
-
-			for _, s := range stones {
+			for _, s := range deletes {
 				for _, iv := range s.intervals {
 					if cf.maxTime < iv.Maxt {
 						cf.maxTime = iv.Maxt
@@ -903,27 +958,16 @@ func (r *walReader) Read(seriesf SeriesCB, samplesf SamplesCB, deletesf DeletesC
 			}
 		}
 	}
+	close(datac)
+	<-donec
 
-	return r.Err()
-}
-
-// 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.files) {
-		return 0, 0, nil, io.EOF
+	if err != nil {
+		return err
 	}
-	cf := r.current()
-
-	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 && r.cur < len(r.files)-1 {
-		// Current reader completed. Leave the file open for later reads
-		// for truncating.
-		r.cur++
-		return r.nextEntry()
+	if r.Err() != nil {
+		return errors.Wrap(r.Err(), "read entry")
 	}
-	return et, flag, b, err
+	return nil
 }
 
 func (r *walReader) at() (WALEntryType, byte, []byte) {
@@ -1043,9 +1087,7 @@ func (r *walReader) entry(cr io.Reader) (WALEntryType, byte, []byte, error) {
 	return etype, flag, buf, nil
 }
 
-func (r *walReader) decodeSeries(flag byte, b []byte) ([]RefSeries, error) {
-	r.seriesBuf = r.seriesBuf[:0]
-
+func (r *walReader) decodeSeries(flag byte, b []byte, res *[]RefSeries) error {
 	dec := decbuf{b: b}
 
 	for len(dec.b) > 0 && dec.err() == nil {
@@ -1059,25 +1101,24 @@ func (r *walReader) decodeSeries(flag byte, b []byte) ([]RefSeries, error) {
 		}
 		sort.Sort(lset)
 
-		r.seriesBuf = append(r.seriesBuf, RefSeries{
+		*res = append(*res, RefSeries{
 			Ref:    ref,
 			Labels: lset,
 		})
 	}
 	if dec.err() != nil {
-		return nil, dec.err()
+		return dec.err()
 	}
 	if len(dec.b) > 0 {
-		return r.seriesBuf, errors.Errorf("unexpected %d bytes left in entry", len(dec.b))
+		return errors.Errorf("unexpected %d bytes left in entry", len(dec.b))
 	}
-	return r.seriesBuf, nil
+	return nil
 }
 
-func (r *walReader) decodeSamples(flag byte, b []byte) ([]RefSample, error) {
+func (r *walReader) decodeSamples(flag byte, b []byte, res *[]RefSample) error {
 	if len(b) == 0 {
-		return nil, nil
+		return nil
 	}
-	r.sampleBuf = r.sampleBuf[:0]
 	dec := decbuf{b: b}
 
 	var (
@@ -1090,7 +1131,7 @@ func (r *walReader) decodeSamples(flag byte, b []byte) ([]RefSample, error) {
 		dtime := dec.varint64()
 		val := dec.be64()
 
-		r.sampleBuf = append(r.sampleBuf, RefSample{
+		*res = append(*res, RefSample{
 			Ref: uint64(int64(baseRef) + dref),
 			T:   baseTime + dtime,
 			V:   math.Float64frombits(val),
@@ -1098,20 +1139,19 @@ func (r *walReader) decodeSamples(flag byte, b []byte) ([]RefSample, error) {
 	}
 
 	if dec.err() != nil {
-		return nil, errors.Wrapf(dec.err(), "decode error after %d samples", len(r.sampleBuf))
+		return errors.Wrapf(dec.err(), "decode error after %d samples", len(*res))
 	}
 	if len(dec.b) > 0 {
-		return r.sampleBuf, errors.Errorf("unexpected %d bytes left in entry", len(dec.b))
+		return errors.Errorf("unexpected %d bytes left in entry", len(dec.b))
 	}
-	return r.sampleBuf, nil
+	return nil
 }
 
-func (r *walReader) decodeDeletes(flag byte, b []byte) ([]Stone, error) {
+func (r *walReader) decodeDeletes(flag byte, b []byte, res *[]Stone) error {
 	dec := &decbuf{b: b}
-	r.tombstoneBuf = r.tombstoneBuf[:0]
 
 	for dec.len() > 0 && dec.err() == nil {
-		r.tombstoneBuf = append(r.tombstoneBuf, Stone{
+		*res = append(*res, Stone{
 			ref: dec.be64(),
 			intervals: Intervals{
 				{Mint: dec.varint64(), Maxt: dec.varint64()},
@@ -1119,10 +1159,10 @@ func (r *walReader) decodeDeletes(flag byte, b []byte) ([]Stone, error) {
 		})
 	}
 	if dec.err() != nil {
-		return nil, dec.err()
+		return dec.err()
 	}
 	if len(dec.b) > 0 {
-		return r.tombstoneBuf, errors.Errorf("unexpected %d bytes left in entry", len(dec.b))
+		return errors.Errorf("unexpected %d bytes left in entry", len(dec.b))
 	}
-	return r.tombstoneBuf, nil
+	return nil
 }
diff --git a/vendor/vendor.json b/vendor/vendor.json
index cbe4cf2d5..50e1577ea 100644
--- a/vendor/vendor.json
+++ b/vendor/vendor.json
@@ -843,28 +843,28 @@
 			"revisionTime": "2016-04-11T19:08:41Z"
 		},
 		{
-			"checksumSHA1": "u1ERYVx8oD5cH3UkQunUTi9n1WI=",
+			"checksumSHA1": "h3i8+wLSIqLvWBWjNPcARM0IQik=",
 			"path": "github.com/prometheus/tsdb",
-			"revision": "4a7c39d9d8e53151f2137df3b16b7173ce435397",
-			"revisionTime": "2017-10-05T07:27:10Z"
+			"revision": "7f8fa07cf7ee8ebde7bdb9ed084f7931c7c0e579",
+			"revisionTime": "2017-10-12T13:27:08Z"
 		},
 		{
 			"checksumSHA1": "Gua979gmISm4cJP/fR2hL8m5To8=",
 			"path": "github.com/prometheus/tsdb/chunks",
-			"revision": "4a7c39d9d8e53151f2137df3b16b7173ce435397",
-			"revisionTime": "2017-10-05T07:27:10Z"
+			"revision": "7f8fa07cf7ee8ebde7bdb9ed084f7931c7c0e579",
+			"revisionTime": "2017-10-12T13:27:08Z"
 		},
 		{
 			"checksumSHA1": "7RhNAVcmDmLFqn9nWiudT0B76f8=",
 			"path": "github.com/prometheus/tsdb/fileutil",
-			"revision": "4a7c39d9d8e53151f2137df3b16b7173ce435397",
-			"revisionTime": "2017-10-05T07:27:10Z"
+			"revision": "7f8fa07cf7ee8ebde7bdb9ed084f7931c7c0e579",
+			"revisionTime": "2017-10-12T13:27:08Z"
 		},
 		{
 			"checksumSHA1": "zhmlvc322RH1L3l9DaA9d/HVVWs=",
 			"path": "github.com/prometheus/tsdb/labels",
-			"revision": "4a7c39d9d8e53151f2137df3b16b7173ce435397",
-			"revisionTime": "2017-10-05T07:27:10Z"
+			"revision": "7f8fa07cf7ee8ebde7bdb9ed084f7931c7c0e579",
+			"revisionTime": "2017-10-12T13:27:08Z"
 		},
 		{
 			"checksumSHA1": "5SYLEhADhdBVZAGPVHWggQl7H8k=",