codec: improve buffer reuse (#10801)

store/mockstore/mocktikv/executor.go

@@ -396,7 +396,7 @@ func (e *indexScanExec) decodeIndexKV(pair Pair) ([][]byte, error) {
 		} else {
 			handleDatum = types.NewIntDatum(handle)
 		}
-		handleBytes, err := codec.EncodeValue(nil, b, handleDatum)
+		handleBytes, err := codec.EncodeValue(nil, nil, handleDatum)
 		if err != nil {
 			return nil, errors.Trace(err)
 		}

tablecodec/tablecodec.go

@@ -235,12 +235,12 @@ func EncodeRow(sc *stmtctx.StatementContext, row []types.Datum, colIDs []int64,
 		values[2*i].SetInt64(id)
 		err := flatten(sc, c, &values[2*i+1])
 		if err != nil {
-			return nil, errors.Trace(err)
+			return valBuf, errors.Trace(err)
 		}
 	}
 	if len(values) == 0 {
 		// We could not set nil value into kv.
-		return []byte{codec.NilFlag}, nil
+		return append(valBuf, codec.NilFlag), nil
 	}
 	return codec.EncodeValue(sc, valBuf, values...)
 }

util/codec/codec.go

@@ -93,7 +93,7 @@ func encode(sc *stmtctx.StatementContext, b []byte, vals []types.Datum, comparab
 			b = append(b, uintFlag)
 			b, err = EncodeMySQLTime(sc, vals[i], mysql.TypeUnspecified, b)
 			if err != nil {
-				return nil, err
+				return b, err
 			}
 		case types.KindMysqlDuration:
 			// duration may have negative value, so we cannot use String to encode directly.
@@ -107,7 +107,7 @@ func encode(sc *stmtctx.StatementContext, b []byte, vals []types.Datum, comparab
 				var bin []byte
 				bin, err = dec.ToHashKey()
 				if err != nil {
-					return nil, errors.Trace(err)
+					return b, errors.Trace(err)
 				}
 				b = append(b, bin...)
 			} else {
@@ -140,7 +140,7 @@ func encode(sc *stmtctx.StatementContext, b []byte, vals []types.Datum, comparab
 		case types.KindMaxValue:
 			b = append(b, maxFlag)
 		default:
-			return nil, errors.Errorf("unsupport encode type %d", vals[i].Kind())
+			return b, errors.Errorf("unsupport encode type %d", vals[i].Kind())
 		}
 	}