Merge sorted pgids rather than resorting everything

.gitignore

@@ -1,3 +1,4 @@
 *.prof
 *.test
+*.swp
 /bin/

freelist.go

@@ -48,15 +48,14 @@ func (f *freelist) pending_count() int {
 
 // all returns a list of all free ids and all pending ids in one sorted list.
 func (f *freelist) all() []pgid {
-	ids := make([]pgid, len(f.ids))
-	copy(ids, f.ids)
+	m := make(pgids, 0)
 
 	for _, list := range f.pending {
-		ids = append(ids, list...)
+		m = append(m, list...)
 	}
 
-	sort.Sort(pgids(ids))
-	return ids
+	sort.Sort(m)
+	return pgids(f.ids).merge(m)
 }
 
 // allocate returns the starting page id of a contiguous list of pages of a given size.
@@ -127,15 +126,17 @@ func (f *freelist) free(txid txid, p *page) {
 
 // release moves all page ids for a transaction id (or older) to the freelist.
 func (f *freelist) release(txid txid) {
+	m := make(pgids, 0)
 	for tid, ids := range f.pending {
 		if tid <= txid {
 			// Move transaction's pending pages to the available freelist.
 			// Don't remove from the cache since the page is still free.
-			f.ids = append(f.ids, ids...)
+			m = append(m, ids...)
 			delete(f.pending, tid)
 		}
 	}
-	sort.Sort(pgids(f.ids))
+	sort.Sort(m)
+	f.ids = pgids(f.ids).merge(m)
 }
 
 // rollback removes the pages from a given pending tx.

freelist_test.go

@@ -1,7 +1,9 @@
 package bolt
 
 import (
+	"math/rand"
 	"reflect"
+	"sort"
 	"testing"
 	"unsafe"
 )
@@ -127,3 +129,28 @@ func TestFreelist_write(t *testing.T) {
 		t.Fatalf("exp=%v; got=%v", exp, f2.ids)
 	}
 }
+
+func Benchmark_FreelistRelease10K(b *testing.B)    { benchmark_FreelistRelease(b, 10000) }
+func Benchmark_FreelistRelease100K(b *testing.B)   { benchmark_FreelistRelease(b, 100000) }
+func Benchmark_FreelistRelease1000K(b *testing.B)  { benchmark_FreelistRelease(b, 1000000) }
+func Benchmark_FreelistRelease10000K(b *testing.B) { benchmark_FreelistRelease(b, 10000000) }
+
+func benchmark_FreelistRelease(b *testing.B, size int) {
+	ids := randomPgids(size)
+	pending := randomPgids(len(ids) / 400)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		f := &freelist{ids: ids, pending: map[txid][]pgid{1: pending}}
+		f.release(1)
+	}
+}
+
+func randomPgids(n int) []pgid {
+	rand.Seed(42)
+	pgids := make(pgids, n)
+	for i := range pgids {
+		pgids[i] = pgid(rand.Int63())
+	}
+	sort.Sort(pgids)
+	return pgids
+}

page.go

@@ -3,6 +3,7 @@ package bolt
 import (
 	"fmt"
 	"os"
+	"sort"
 	"unsafe"
 )
 
@@ -132,3 +133,40 @@ type pgids []pgid
 func (s pgids) Len() int           { return len(s) }
 func (s pgids) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
 func (s pgids) Less(i, j int) bool { return s[i] < s[j] }
+
+// merge returns the sorted union of a and b.
+func (a pgids) merge(b pgids) pgids {
+	// Return the opposite slice if one is nil.
+	if len(a) == 0 {
+		return b
+	} else if len(b) == 0 {
+		return a
+	}
+
+	// Create a list to hold all elements from both lists.
+	merged := make(pgids, 0, len(a)+len(b))
+
+	// Assign lead to the slice with a lower starting value, follow to the higher value.
+	lead, follow := a, b
+	if b[0] < a[0] {
+		lead, follow = b, a
+	}
+
+	// Continue while there are elements in the lead.
+	for len(lead) > 0 {
+		// Merge largest prefix of lead that is ahead of follow[0].
+		n := sort.Search(len(lead), func(i int) bool { return lead[i] > follow[0] })
+		merged = append(merged, lead[:n]...)
+		if n >= len(lead) {
+			break
+		}
+
+		// Swap lead and follow.
+		lead, follow = follow, lead[n:]
+	}
+
+	// Append what's left in follow.
+	merged = append(merged, follow...)
+
+	return merged
+}

page_test.go

@@ -1,7 +1,10 @@
 package bolt
 
 import (
+	"reflect"
+	"sort"
 	"testing"
+	"testing/quick"
 )
 
 // Ensure that the page type can be returned in human readable format.
@@ -27,3 +30,43 @@ func TestPage_typ(t *testing.T) {
 func TestPage_dump(t *testing.T) {
 	(&page{id: 256}).hexdump(16)
 }
+
+func TestPgids_merge(t *testing.T) {
+	a := pgids{4, 5, 6, 10, 11, 12, 13, 27}
+	b := pgids{1, 3, 8, 9, 25, 30}
+	c := a.merge(b)
+	if !reflect.DeepEqual(c, pgids{1, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 25, 27, 30}) {
+		t.Errorf("mismatch: %v", c)
+	}
+
+	a = pgids{4, 5, 6, 10, 11, 12, 13, 27, 35, 36}
+	b = pgids{8, 9, 25, 30}
+	c = a.merge(b)
+	if !reflect.DeepEqual(c, pgids{4, 5, 6, 8, 9, 10, 11, 12, 13, 25, 27, 30, 35, 36}) {
+		t.Errorf("mismatch: %v", c)
+	}
+}
+
+func TestPgids_merge_quick(t *testing.T) {
+	if err := quick.Check(func(a, b pgids) bool {
+		// Sort incoming lists.
+		sort.Sort(a)
+		sort.Sort(b)
+
+		// Merge the two lists together.
+		got := a.merge(b)
+
+		// The expected value should be the two lists combined and sorted.
+		exp := append(a, b...)
+		sort.Sort(exp)
+
+		if !reflect.DeepEqual(exp, got) {
+			t.Errorf("\nexp=%+v\ngot=%+v\n", exp, got)
+			return false
+		}
+
+		return true
+	}, nil); err != nil {
+		t.Fatal(err)
+	}
+}