mem: Avoid clearing new buffers and clear buffers from simpleBufferPools (#8670)

RELEASE NOTES:
* mem:
  * Avoid clearing buffers which newly allocated.
  * Clear large buffers (> 1MB) before re-using.

Author: arjan-bal

mem/buffer_pool.go

@@ -118,7 +118,11 @@ type sizedBufferPool struct {
 }
 
 func (p *sizedBufferPool) Get(size int) *[]byte {
-	buf := p.pool.Get().(*[]byte)
+	buf, ok := p.pool.Get().(*[]byte)
+	if !ok {
+		buf := make([]byte, size, p.defaultSize)
+		return &buf
+	}
 	b := *buf
 	clear(b[:cap(b)])
 	*buf = b[:size]
@@ -137,12 +141,6 @@ func (p *sizedBufferPool) Put(buf *[]byte) {
 
 func newSizedBufferPool(size int) *sizedBufferPool {
 	return &sizedBufferPool{
-		pool: sync.Pool{
-			New: func() any {
-				buf := make([]byte, size)
-				return &buf
-			},
-		},
 		defaultSize: size,
 	}
 }
@@ -160,6 +158,7 @@ type simpleBufferPool struct {
 func (p *simpleBufferPool) Get(size int) *[]byte {
 	bs, ok := p.pool.Get().(*[]byte)
 	if ok && cap(*bs) >= size {
+		clear((*bs)[:cap(*bs)])
 		*bs = (*bs)[:size]
 		return bs
 	}

mem/buffer_pool_test.go

@@ -49,26 +49,44 @@ func (s) TestBufferPool(t *testing.T) {
 }
 
 func (s) TestBufferPoolClears(t *testing.T) {
-	pool := mem.NewTieredBufferPool(4)
+	const poolSize = 4
+	pool := mem.NewTieredBufferPool(poolSize)
+	tests := []struct {
+		name       string
+		bufferSize int
+	}{
+		{
+			name:       "sized_buffer_pool",
+			bufferSize: poolSize,
+		},
+		{
+			name:       "simple_buffer_pool",
+			bufferSize: poolSize + 1,
+		},
+	}
 
-	for {
-		buf1 := pool.Get(4)
-		copy(*buf1, "1234")
-		pool.Put(buf1)
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			for {
+				buf1 := pool.Get(tc.bufferSize)
+				copy(*buf1, "1234")
+				pool.Put(buf1)
 
-		buf2 := pool.Get(4)
-		if unsafe.SliceData(*buf1) != unsafe.SliceData(*buf2) {
-			pool.Put(buf2)
-			// This test is only relevant if a buffer is reused, otherwise try again. This
-			// can happen if a GC pause happens between putting the buffer back in the pool
-			// and getting a new one.
-			continue
-		}
+				buf2 := pool.Get(tc.bufferSize)
+				if unsafe.SliceData(*buf1) != unsafe.SliceData(*buf2) {
+					pool.Put(buf2)
+					// This test is only relevant if a buffer is reused, otherwise try again. This
+					// can happen if a GC pause happens between putting the buffer back in the pool
+					// and getting a new one.
+					continue
+				}
 
-		if !bytes.Equal(*buf1, make([]byte, 4)) {
-			t.Fatalf("buffer not cleared")
-		}
-		break
+				if !bytes.Equal(*buf1, make([]byte, tc.bufferSize)) {
+					t.Fatalf("buffer not cleared")
+				}
+				break
+			}
+		})
 	}
 }