Merge pull request #9519 from gyuho/heap

lease: remove unnecessary O(log N) heap operation when nothing is expiry

lease/lease_queue.go

@@ -14,8 +14,9 @@
 
 package lease
 
+// LeaseWithTime contains lease object with expire information.
 type LeaseWithTime struct {
-	leaseId    LeaseID
+	id         LeaseID
 	expiration int64
 	index      int
 }

lease/lease_queue_test.go

@@ -0,0 +1,59 @@
+// Copyright 2018 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package lease
+
+import (
+	"container/heap"
+	"testing"
+	"time"
+)
+
+func TestLeaseQueue(t *testing.T) {
+	le := &lessor{
+		leaseHeap: make(LeaseQueue, 0),
+		leaseMap:  make(map[LeaseID]*Lease),
+	}
+	heap.Init(&le.leaseHeap)
+
+	// insert in reverse order of expiration time
+	for i := 50; i >= 1; i-- {
+		exp := time.Now().Add(time.Hour).UnixNano()
+		if i == 1 {
+			exp = time.Now().UnixNano()
+		}
+		le.leaseMap[LeaseID(i)] = &Lease{ID: LeaseID(i)}
+		heap.Push(&le.leaseHeap, &LeaseWithTime{id: LeaseID(i), expiration: exp})
+	}
+
+	// first element must be front
+	if le.leaseHeap[0].id != LeaseID(1) {
+		t.Fatalf("first item expected lease ID %d, got %d", LeaseID(1), le.leaseHeap[0].id)
+	}
+
+	l, ok, more := le.expireExists()
+	if l.ID != 1 {
+		t.Fatalf("first item expected lease ID %d, got %d", 1, l.ID)
+	}
+	if !ok {
+		t.Fatal("expect expiry lease exists")
+	}
+	if more {
+		t.Fatal("expect no more expiry lease")
+	}
+
+	if le.leaseHeap.Len() != 49 {
+		t.Fatalf("expected lease heap pop, got %d", le.leaseHeap.Len())
+	}
+}

lease/lessor.go

@@ -235,7 +235,7 @@ func (le *lessor) Grant(id LeaseID, ttl int64) (*Lease, error) {
 	}
 
 	le.leaseMap[id] = l
-	item := &LeaseWithTime{leaseId: l.ID, expiration: l.expiry.UnixNano()}
+	item := &LeaseWithTime{id: l.ID, expiration: l.expiry.UnixNano()}
 	heap.Push(&le.leaseHeap, item)
 	l.persistTo(le.b)
 
@@ -319,7 +319,7 @@ func (le *lessor) Renew(id LeaseID) (int64, error) {
 	}
 
 	l.refresh(0)
-	item := &LeaseWithTime{leaseId: l.ID, expiration: l.expiry.UnixNano()}
+	item := &LeaseWithTime{id: l.ID, expiration: l.expiry.UnixNano()}
 	heap.Push(&le.leaseHeap, item)
 	return l.ttl, nil
 }
@@ -355,7 +355,7 @@ func (le *lessor) Promote(extend time.Duration) {
 	// refresh the expiries of all leases.
 	for _, l := range le.leaseMap {
 		l.refresh(extend)
-		item := &LeaseWithTime{leaseId: l.ID, expiration: l.expiry.UnixNano()}
+		item := &LeaseWithTime{id: l.ID, expiration: l.expiry.UnixNano()}
 		heap.Push(&le.leaseHeap, item)
 	}
 
@@ -392,7 +392,7 @@ func (le *lessor) Promote(extend time.Duration) {
 		delay := time.Duration(rateDelay)
 		nextWindow = baseWindow + delay
 		l.refresh(delay + extend)
-		item := &LeaseWithTime{leaseId: l.ID, expiration: l.expiry.UnixNano()}
+		item := &LeaseWithTime{id: l.ID, expiration: l.expiry.UnixNano()}
 		heap.Push(&le.leaseHeap, item)
 	}
 }
@@ -521,28 +521,50 @@ func (le *lessor) runLoop() {
 	}
 }
 
+// expireExists returns true if expiry items exist.
+// It pops only when expiry item exists.
+// "next" is true, to indicate that it may exist in next attempt.
+func (le *lessor) expireExists() (l *Lease, ok bool, next bool) {
+	if le.leaseHeap.Len() == 0 {
+		return nil, false, false
+	}
+
+	item := le.leaseHeap[0]
+	l = le.leaseMap[item.id]
+	if l == nil {
+		// lease has expired or been revoked
+		// no need to revoke (nothing is expiry)
+		heap.Pop(&le.leaseHeap) // O(log N)
+		return nil, false, true
+	}
+
+	if time.Now().UnixNano() < item.expiration {
+		// Candidate expirations are caught up, reinsert this item
+		// and no need to revoke (nothing is expiry)
+		return l, false, false
+	}
+	// if the lease is actually expired, add to the removal list. If it is not expired, we can ignore it because another entry will have been inserted into the heap
+
+	heap.Pop(&le.leaseHeap) // O(log N)
+	return l, true, false
+}
+
 // findExpiredLeases loops leases in the leaseMap until reaching expired limit
 // and returns the expired leases that needed to be revoked.
 func (le *lessor) findExpiredLeases(limit int) []*Lease {
 	leases := make([]*Lease, 0, 16)
 
 	for {
-		if le.leaseHeap.Len() == 0 {
+		l, ok, next := le.expireExists()
+		if !ok && !next {
 			break
 		}
-
-		item := heap.Pop(&le.leaseHeap).(*LeaseWithTime)
-		l := le.leaseMap[item.leaseId]
-		if l == nil {
-			// lease has expired or been revoked, continue
+		if !ok {
 			continue
 		}
-		if time.Now().UnixNano() < item.expiration {
-			// Candidate expirations are caught up, reinsert this item
-			heap.Push(&le.leaseHeap, item)
-			break
+		if next {
+			continue
 		}
-		// if the lease is actually expired, add to the removal list. If it is not expired, we can ignore it because another entry will have been inserted into the heap
 
 		if l.expired() {
 			leases = append(leases, l)