pre allocate cache key for the block cache and the bloom filter cache (…

…#1371)

Signed-off-by: Tiger <[email protected]>

table/table.go

@@ -596,11 +596,13 @@ func (t *Table) block(idx int) (*block, error) {
 // bfCacheKey returns the cache key for bloom filter.
 func (t *Table) bfCacheKey() []byte {
 	y.AssertTrue(t.id < math.MaxUint32)
-	buf := make([]byte, 4)
-	binary.BigEndian.PutUint32(buf, uint32(t.id))
-
+	buf := make([]byte, 6)
 	// Without the "bf" prefix, we will have conflict with the blockCacheKey.
-	return append([]byte("bf"), buf...)
+	buf[0] = 'b'
+	buf[1] = 'f'
+
+	binary.BigEndian.PutUint32(buf[2:], uint32(t.id))
+	return buf
 }
 
 func (t *Table) blockCacheKey(idx int) []byte {
@@ -617,10 +619,12 @@ func (t *Table) blockCacheKey(idx int) []byte {
 // blockOffsetsCacheKey returns the cache key for block offsets.
 func (t *Table) blockOffsetsCacheKey() []byte {
 	y.AssertTrue(t.id < math.MaxUint32)
-	buf := make([]byte, 4, 6)
-	binary.BigEndian.PutUint32(buf, uint32(t.id))
+	buf := make([]byte, 6)
+	buf[0] = 'b'
+	buf[1] = 'o'
 
-	return append([]byte("bo"), buf...)
+	binary.BigEndian.PutUint32(buf[2:], uint32(t.id))
+	return buf
 }
 
 // EstimatedSize returns the total size of key-values stored in this table (including the