FlatBuffers与protobuf性能比较
FlatBuffers发布时，顺便也公布了它的性能数据，具体数据请见Benchmark。
它的测试用例由以下数据构成"a set of about 10 objects containing an array, 4 strings, and a large variety of int/float scalar values of all sizes, meant to be representative of game data, e.g. a scene format."
我感觉这样测试如同儿戏，便自己设计了一个测试用例，主要关注CPU计算时间和内存空间占用两个指标，参考对象是protobuf。
测试用例为：序列化一个通讯录personal_info_list（table），通讯录可以认为是有每个人的信息(personal_info)的集合。每个人信息personal_info(table)有：个人id(uint)、名字(string)、年龄(byte)、性别(enum, byte)和电话号码(ulong)。本来我想用struct表示personal_info(table)，但是struct不允许有数组或string成员，无奈我用table描述它了。相应的idl文件如下：
//
FILE : tellist.fbs
DESC : basic message for msg-center
AUTHOR : v 0.1 written by Alex Stocks on June 22, 2014
LICENCE :
MOD :
namespace as.tellist;
enum GENDER_TYPE : byte
{
MALE = 0,
FEMALE = 1,
OTHER = 2
}
table personal_info
{
id : uint;
name : string;
age : byte;
gender : GENDER_TYPE;
phone_num : ulong;
}
table personal_info_list
{
info : [personal_info];
}
root_type personal_info_list;
因为要以protobuf做性能参考，列出protobuf的idl文件如下：
//
FILE : tellist.proto
DESC : basic message for msg-center
AUTHOR : v 0.1 written by Alex Stocks on June 22, 2014
LICENCE :
MOD :
package as.tellist;
enum gender_type
{
MALE = 0;
FEMALE = 1;
OTHER = 2;
}
message personal_info
{
optional uint32 id = 1;
optional string name = 2;
optional uint32 age = 3;
optional gender_type gender = 4;
optional uint64 phone_num = 5;
}
message personal_info_list
{
repeated personal_info info = 1;
}若用C的struct描述对应的头文件(其对应的程序称之为“二进制”)，如下：
/**
* FILE : tellist.h
* DESC : to test tellist
* AUTHOR : v1.0 written by Alex Stocks
* DATE : on June 28, 2014
* LICENCE : GPL 2.0
* MOD :
**/
#ifndef __TELLIST_H__
#define __TELLIST_H__
enum
{
GENDER_TYPE_MALE = 0,
GENDER_TYPE_FEMALE = 1,
GENDER_TYPE_OTHER = 2,
};
inline const char **EnumNamesGENDER_TYPE()
{
static const char *names[] = { "MALE", "FEMALE", "OTHER"};
return names;
}
inline const char *EnumNameGENDER_TYPE(int e)
{
return EnumNamesGENDER_TYPE()[e];
}
typedef struct personal_info_tag
{
unsigned id;
unsigned char age;
char gender;
unsigned long long phone_num;
char name[32];
} personal_info;
typedef struct personal_info_list_tag
{
int size;
personal_info info[0];
} personal_info_list;
#endif
// the end of the header file tellist.h
测试时，在内存中构造37个personal_info对象，并序列化之，重复这个过程100万次，然后再进行反序列化，再重复100万次。
测试结果如下(补充：tellist_pb是protobuf测试程序，tellist_fb是FlatBuffers测试程序，tellist_fb是二进制测试程序，)：
测试环境：12Core Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz
free
total used free shared buffers cached
Mem: 66081944 62222028 3859916 0 196448 43690828
-/+ buffers/cache: 18334752 47747192
Swap: 975864 855380 120484
protobuf三次测试结果：
bin/tellist_pb
encode: loop = 1000000, time diff = 14210ms
decode: loop = 1000000, time diff = 11185ms
buf size:841
bin/tellist_pb
encode: loop = 1000000, time diff = 14100ms
decode: loop = 1000000, time diff = 11234ms
buf size:841
bin/tellist_pb
encode: loop = 1000000, time diff = 14145ms
decode: loop = 1000000, time diff = 11237ms
buf size:841
序列化后占用内存空间841Byte，encode平均运算时间42455ms / 3 = 14151.7ms，decode平均计算时间33656ms / 3 = 11218.7ms
flatbuffers三次测试结果：
bin/tellist_fb
encode: loop = 1000000, time diff = 11666ms
decode: loop = 1000000, time diff = 1141ms
buf size:1712
bin/tellist_fb
encode: loop = 1000000, time diff = 11539ms
decode: loop = 1000000, time diff = 1200ms
buf size:1712
bin/tellist_fb
encode: loop = 1000000, time diff = 11737ms
decode: loop = 1000000, time diff = 1141ms
buf size:1712
序列化后占用内存空间1712Byte，encode平均运算时间34942ms / 3 = 11647.3ms，decode平均计算时间3482ms / 3 = 1160.7ms
二进制三次测试结果：
bin/tellist
encode: loop = 1000000, time diff = 4967ms
decode: loop = 1000000, time diff = 688ms
buf size:304
bin/tellist
encode: loop = 1000000, time diff = 4971ms
decode: loop = 1000000, time diff = 687ms
buf size:304
bin/tellist
encode: loop = 1000000, time diff = 4966ms
decode: loop = 1000000, time diff = 686ms
buf size:304
序列化后占用内存空间304Byte，encode平均运算时间14904ms / 3 = 4968ms，decode平均计算时间2061ms / 3 = 687ms
测试环境：1 Core Intel(R) Core(TM) i5-3210M CPU @ 2.50GHz
free
total used free shared buffers cached
Mem: 753932 356036 397896 0 50484 224848
-/+ buffers/cache: 80704 673228
Swap: 1324028 344 1323684
protobuf三次测试结果：
./bin/tellist_pb
encode: loop = 1000000, time diff = 12451ms
decode: loop = 1000000, time diff = 9662ms
buf size:841
./bin/tellist_pb
encode: loop = 1000000, time diff = 12545ms
decode: loop = 1000000, time diff = 9840ms
buf size:841
./bin/tellist_pb
encode: loop = 1000000, time diff = 12554ms
decode: loop = 1000000, time diff = 10460ms
buf size:841
序列化后占用内存空间841Byte，encode平均运算时间37550ms / 3 = 12516.7ms，decode平均计算时间29962ms / 3 = 9987.3ms
flatbuffers三次测试结果：
bin/tellist_fb
encode: loop = 1000000, time diff = 9640ms
decode: loop = 1000000, time diff = 1164ms
buf size:1712
bin/tellist_fb
encode: loop = 1000000, time diff = 9595ms
decode: loop = 1000000, time diff = 1170ms
buf size:1712
bin/tellist_fb
encode: loop = 1000000, time diff = 9570ms
decode: loop = 1000000, time diff = 1172ms
buf size:1712
序列化后占用内存空间1712Byte，encode平均运算时间28805ms / 3 = 9345ms，decode平均计算时间3506ms / 3 = 1168.7ms
二进制三次测试结果：
bin/tellist
encode: loop = 1000000, time diff = 4194ms
decode: loop = 1000000, time diff = 538ms
buf size:304
bin/tellist
encode: loop = 1000000, time diff = 4387ms
decode: loop = 1000000, time diff = 544ms
buf size:304
bin/tellist
encode: loop = 1000000, time diff = 4181ms
decode: loop = 1000000, time diff = 533ms
buf size:304
序列化后占用内存空间304Byte，encode平均运算时间12762ms / 3 = 4254ms，decode平均计算时间1615ms / 3 = 538.3ms
上面的二进制程序的结果无论在内存空间占用还是cpu计算时间这两个指标上都是最快的。但本文只讨论FlatBuffers和protobuf，所以不让它的结果参与比较。
从以上数据看出，在内存空间占用这个指标上，FlatBuffers占用的内存空间比protobuf多了两倍。序列化时二者的cpu计算时间FB比PB快了3000ms左右，反序列化时二者的cpu计算时间FB比PB快了9000ms左右。FB在计算时间上占优势，而PB则在内存空间上占优（相比FB，这也正是它计算时间比较慢的原因）。
上面的测试环境是在公司的linux server端和我自己的mac pro分别进行的。请手机端开发者自己也在手机端进行下测试， 应该能得到类似的结果。Google宣称FB适合游戏开发是有道理的，如果在乎计算时间我想它也适用于后台开发。
另外，FB大量使用了C++11的语法，其从idl生成的代码接口不如protubuf友好。不过相比使用protobuf时的一堆头文件和占18M之多的lib库，FlatBuffers仅仅一个"flatbuffers/flatbuffers.h"就足够了。
测试程序已经上传到百度网盘，点击这个链接即可下载。欢迎各位的批评意见。