diff --git a/ingester/ingester.go b/ingester/ingester.go
index c597667a72..09dc7edb1b 100644
--- a/ingester/ingester.go
+++ b/ingester/ingester.go
@@ -19,9 +19,7 @@ import (
 )
 
 const (
-	ingesterSubsystem        = "ingester"
-	maxConcurrentFlushSeries = 100
-
+	ingesterSubsystem  = "ingester"
 	discardReasonLabel = "reason"
 
 	// Reasons to discard samples.
@@ -40,6 +38,11 @@ var (
 		"The current number of users in memory.",
 		nil, nil,
 	)
+	flushQueueLengthDesc = prometheus.NewDesc(
+		"cortex_ingester_flush_queue_length",
+		"The total number of series pending in the flush queue.",
+		nil, nil,
+	)
 
 	// ErrOutOfOrderSample is returned if a sample has a timestamp before the latest
 	// timestamp in the series it is appended to.
@@ -64,7 +67,9 @@ type Ingester struct {
 	userStateLock sync.Mutex
 	userState     map[string]*userState
 
-	flushQueue *priorityQueue
+	// One queue per flush thread.  Fingerprint is used to
+	// pick a queue.
+	flushQueues []*priorityQueue
 
 	ingestedSamples    prometheus.Counter
 	discardedSamples   *prometheus.CounterVec
@@ -136,9 +141,8 @@ func New(cfg Config, chunkStore cortex.Store) (*Ingester, error) {
 		chunkStore: chunkStore,
 		quit:       make(chan struct{}),
 
-		userState: map[string]*userState{},
-
-		flushQueue: newPriorityQueue(),
+		userState:   map[string]*userState{},
+		flushQueues: make([]*priorityQueue, cfg.ConcurrentFlushes, cfg.ConcurrentFlushes),
 
 		ingestedSamples: prometheus.NewCounter(prometheus.CounterOpts{
 			Name: "cortex_ingester_ingested_samples_total",
@@ -186,7 +190,8 @@ func New(cfg Config, chunkStore cortex.Store) (*Ingester, error) {
 
 	i.done.Add(cfg.ConcurrentFlushes)
 	for j := 0; j < cfg.ConcurrentFlushes; j++ {
-		go i.flushLoop()
+		i.flushQueues[j] = newPriorityQueue()
+		go i.flushLoop(j)
 	}
 
 	i.done.Add(1)
@@ -439,7 +444,9 @@ func (i *Ingester) loop() {
 
 		// We close flush queue here to ensure the flushLoops pick
 		// up all the flushes triggered by the last run
-		i.flushQueue.Close()
+		for _, flushQueue := range i.flushQueues {
+			flushQueue.Close()
+		}
 
 		log.Infof("Ingester.loop() exited gracefully")
 		i.done.Done()
@@ -503,7 +510,7 @@ func (i *Ingester) flushSeries(u *userState, fp model.Fingerprint, series *memor
 
 	// Decide what chunks to flush
 	firstTime := series.head().FirstTime()
-	if immediate || model.Now().Sub(series.head().FirstTime()) > i.cfg.MaxChunkAge {
+	if immediate || model.Now().Sub(firstTime) > i.cfg.MaxChunkAge {
 		series.headChunkClosed = true
 		series.head().MaybePopulateLastTime()
 	}
@@ -517,17 +524,18 @@ func (i *Ingester) flushSeries(u *userState, fp model.Fingerprint, series *memor
 		return
 	}
 
-	i.flushQueue.Enqueue(&flushOp{firstTime, u.userID, fp, immediate})
+	flushQueueIndex := int(uint64(fp) % uint64(i.cfg.ConcurrentFlushes))
+	i.flushQueues[flushQueueIndex].Enqueue(&flushOp{firstTime, u.userID, fp, immediate})
 }
 
-func (i *Ingester) flushLoop() {
+func (i *Ingester) flushLoop(j int) {
 	defer func() {
 		log.Info("Ingester.flushLoop() exited")
 		i.done.Done()
 	}()
 
 	for {
-		o := i.flushQueue.Dequeue()
+		o := i.flushQueues[j].Dequeue()
 		if o == nil {
 			return
 		}
@@ -551,10 +559,14 @@ func (i *Ingester) flushLoop() {
 		userState.fpLocker.Lock(op.fp)
 		chunks := series.chunkDescs
 		if !series.headChunkClosed {
-			chunks = chunks[1:]
+			chunks = chunks[:len(chunks)-1]
 		}
 		userState.fpLocker.Unlock(op.fp)
 
+		if len(chunks) == 0 {
+			continue
+		}
+
 		// flush the chunks without locking the series
 		if err := i.flushChunks(ctx, op.fp, series.metric, chunks); err != nil {
 			log.Errorf("Failed to flush chunks: %v", err)
@@ -610,6 +622,7 @@ func (i *Ingester) updateRates() {
 func (i *Ingester) Describe(ch chan<- *prometheus.Desc) {
 	ch <- memorySeriesDesc
 	ch <- memoryUsersDesc
+	ch <- flushQueueLengthDesc
 	ch <- i.ingestedSamples.Desc()
 	i.discardedSamples.Describe(ch)
 	ch <- i.chunkUtilization.Desc()
@@ -641,6 +654,16 @@ func (i *Ingester) Collect(ch chan<- prometheus.Metric) {
 		prometheus.GaugeValue,
 		float64(numUsers),
 	)
+
+	flushQueueLength := 0
+	for _, flushQueue := range i.flushQueues {
+		flushQueueLength += flushQueue.Length()
+	}
+	ch <- prometheus.MustNewConstMetric(
+		flushQueueLengthDesc,
+		prometheus.GaugeValue,
+		float64(flushQueueLength),
+	)
 	ch <- i.ingestedSamples
 	i.discardedSamples.Collect(ch)
 	ch <- i.chunkUtilization
diff --git a/ingester/priority_queue.go b/ingester/priority_queue.go
index 28f2329aad..6044b26921 100644
--- a/ingester/priority_queue.go
+++ b/ingester/priority_queue.go
@@ -15,13 +15,13 @@ type priorityQueue struct {
 
 type op interface {
 	Key() string
-	Priority() int64
+	Priority() int64 // The larger the number the higher the priority.
 }
 
 type queue []op
 
 func (q queue) Len() int           { return len(q) }
-func (q queue) Less(i, j int) bool { return q[i].Priority() < q[j].Priority() }
+func (q queue) Less(i, j int) bool { return q[i].Priority() > q[j].Priority() }
 func (q queue) Swap(i, j int)      { q[i], q[j] = q[j], q[i] }
 
 // Push and Pop use pointer receivers because they modify the slice's length,
@@ -47,6 +47,12 @@ func newPriorityQueue() *priorityQueue {
 	return pq
 }
 
+func (pq *priorityQueue) Length() int {
+	pq.lock.Lock()
+	defer pq.lock.Unlock()
+	return len(pq.queue)
+}
+
 func (pq *priorityQueue) Close() {
 	pq.lock.Lock()
 	defer pq.lock.Unlock()
@@ -67,10 +73,13 @@ func (pq *priorityQueue) Enqueue(op op) {
 		return
 	}
 
+	pq.hit[op.Key()] = struct{}{}
 	heap.Push(&pq.queue, op)
 	pq.cond.Broadcast()
 }
 
+// Dequeue will return the op with the highest priority; block if queue is
+// empty; returns nil if queue is closed.
 func (pq *priorityQueue) Dequeue() op {
 	pq.lock.Lock()
 	defer pq.lock.Unlock()
diff --git a/ingester/priority_queue_test.go b/ingester/priority_queue_test.go
new file mode 100644
index 0000000000..105547c484
--- /dev/null
+++ b/ingester/priority_queue_test.go
@@ -0,0 +1,89 @@
+package ingester
+
+import (
+	"runtime"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type item int64
+
+func (i item) Priority() int64 {
+	return int64(i)
+}
+
+func (i item) Key() string {
+	return strconv.FormatInt(int64(i), 10)
+}
+
+func TestPriorityQueueBasic(t *testing.T) {
+	queue := newPriorityQueue()
+	assert.Equal(t, 0, queue.Length(), "Expected length = 0")
+
+	queue.Enqueue(item(1))
+	assert.Equal(t, 1, queue.Length(), "Expected length = 1")
+
+	i, ok := queue.Dequeue().(item)
+	assert.True(t, ok, "Expected cast to succeed")
+	assert.Equal(t, item(1), i, "Expected to dequeue item(1)")
+
+	queue.Close()
+	assert.Nil(t, queue.Dequeue(), "Expect nil dequeue")
+}
+
+func TestPriorityQueuePriorities(t *testing.T) {
+	queue := newPriorityQueue()
+	queue.Enqueue(item(1))
+	queue.Enqueue(item(2))
+
+	assert.Equal(t, item(2), queue.Dequeue().(item), "Expected to dequeue item(2)")
+	assert.Equal(t, item(1), queue.Dequeue().(item), "Expected to dequeue item(1)")
+
+	queue.Close()
+	assert.Nil(t, queue.Dequeue(), "Expect nil dequeue")
+}
+
+func TestPriorityQueuePriorities2(t *testing.T) {
+	queue := newPriorityQueue()
+	queue.Enqueue(item(2))
+	queue.Enqueue(item(1))
+
+	assert.Equal(t, item(2), queue.Dequeue().(item), "Expected to dequeue item(2)")
+	assert.Equal(t, item(1), queue.Dequeue().(item), "Expected to dequeue item(1)")
+
+	queue.Close()
+	assert.Nil(t, queue.Dequeue(), "Expect nil dequeue")
+}
+
+func TestPriorityQueueDedupe(t *testing.T) {
+	queue := newPriorityQueue()
+	queue.Enqueue(item(1))
+	queue.Enqueue(item(1))
+
+	assert.Equal(t, 1, queue.Length(), "Expected length = 1")
+	assert.Equal(t, item(1), queue.Dequeue().(item), "Expected to dequeue item(1)")
+
+	queue.Close()
+	assert.Nil(t, queue.Dequeue(), "Expect nil dequeue")
+}
+
+func TestPriorityQueueWait(t *testing.T) {
+	queue := newPriorityQueue()
+
+	done := make(chan struct{})
+	go func() {
+		assert.Nil(t, queue.Dequeue(), "Expect nil dequeue")
+		close(done)
+	}()
+
+	runtime.Gosched()
+	queue.Close()
+	select {
+	case <-done:
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("Close didn't unblock Dequeue.")
+	}
+}