本文所引用的源码全部来自Redis2.8.2版本。
Redis AOF数据持久化机制的实现相关代码是redis.c, redis.h, aof.c, bio.c, rio.c, config.c
在阅读本文之前请先阅读Redis数据持久化机制AOF原理分析之配置详解文章，了解AOF相关参数的解析，文章链接
http://blog.csdn.net/acceptedxukai/article/details/18135219
转载请注明，文章出自http://blog.csdn.net/acceptedxukai/article/details/18136903
下面将介绍AOF数据持久化机制的实现
Server启动加载AOF文件数据
Server启动加载AOF文件数据的执行步骤为:main() -> initServerConfig() -> loadServerConfig() -> initServer() -> loadDataFromDisk()。initServerConfig()主要为初始化默认的AOF参数配置；loadServerConfig()加载配置文件redis.conf中AOF的参数配置，覆盖Server的默认AOF参数配置，如果配置appendonly on，那么AOF数据持久化功能将被激活，server.aof_state参数被设置为REDIS_AOF_ON；loadDataFromDisk()判断server.aof_state == REDIS_AOF_ON，结果为True就调用loadAppendOnlyFile函数加载AOF文件中的数据，加载的方法就是读取AOF文件中数据，由于AOF文件中存储的数据与客户端发送的请求格式相同完全符合Redis的通信协议，因此Server创建伪客户端fakeClient，将解析后的AOF文件数据像客户端请求一样调用各种指令，cmd->proc(fakeClient)，将AOF文件中的数据重现到Redis Server数据库中。
/* Function called at startup to load RDB or AOF file in memory. */
void loadDataFromDisk(void) {
long long start = ustime();
if (server.aof_state == REDIS_AOF_ON) {
if (loadAppendOnlyFile(server.aof_filename) == REDIS_OK)
redisLog(REDIS_NOTICE,"DB loaded from append only file: %.3f seconds",(float)(ustime()-start)/1000000);
} else {
if (rdbLoad(server.rdb_filename) == REDIS_OK) {
redisLog(REDIS_NOTICE,"DB loaded from disk: %.3f seconds",
(float)(ustime()-start)/1000000);
} else if (errno != ENOENT) {
redisLog(REDIS_WARNING,"Fatal error loading the DB: %s. Exiting.",strerror(errno));
exit(1);
}
}
}
Server首先判断加载AOF文件是因为AOF文件中的数据要比RDB文件中的数据要新。
int loadAppendOnlyFile(char *filename) {
struct redisClient *fakeClient;
FILE *fp = fopen(filename,"r");
struct redis_stat sb;
int old_aof_state = server.aof_state;
long loops = 0;
//redis_fstat就是fstat64函数，通过fileno(fp)得到文件描述符，获取文件的状态存储于sb中，
//具体可以参考stat函数，st_size就是文件的字节数
if (fp && redis_fstat(fileno(fp),&sb) != -1 && sb.st_size == 0) {
server.aof_current_size = 0;
fclose(fp);
return REDIS_ERR;
}
if (fp == NULL) {//打开文件失败
redisLog(REDIS_WARNING,"Fatal error: can't open the append log file for reading: %s",strerror(errno));
exit(1);
}
/* Temporarily disable AOF, to prevent EXEC from feeding a MULTI
* to the same file we're about to read. */
server.aof_state = REDIS_AOF_OFF;
fakeClient = createFakeClient(); //建立伪终端
startLoading(fp); // 定义于 rdb.c ，更新服务器的载入状态
while(1) {
int argc, j;
unsigned long len;
robj **argv;
char buf[128];
sds argsds;
struct redisCommand *cmd;
/* Serve the clients from time to time */
// 有间隔地处理外部请求，ftello()函数得到文件的当前位置，返回值为long
if (!(loops++ % 1000)) {
loadingProgress(ftello(fp));//保存aof文件读取的位置，ftellno(fp)获取文件当前位置
aeProcessEvents(server.el, AE_FILE_EVENTS|AE_DONT_WAIT);//处理事件
}
//按行读取AOF数据
if (fgets(buf,sizeof(buf),fp) == NULL) {
if (feof(fp))//达到文件尾EOF
break;
else
goto readerr;
}
//读取AOF文件中的命令，依照Redis的协议处理
if (buf[0] != '*') goto fmterr;
argc = atoi(buf+1);//参数个数
if (argc < 1) goto fmterr;
argv = zmalloc(sizeof(robj*)*argc);//参数值
for (j = 0; j < argc; j++) {
if (fgets(buf,sizeof(buf),fp) == NULL) goto readerr;
if (buf[0] != '$') goto fmterr;
len = strtol(buf+1,NULL,10);//每个bulk的长度
argsds = sdsnewlen(NULL,len);//新建一个空sds
//按照bulk的长度读取
if (len && fread(argsds,len,1,fp) == 0) goto fmterr;
argv[j] = createObject(REDIS_STRING,argsds);
if (fread(buf,2,1,fp) == 0) goto fmterr; /* discard CRLF 跳过\r\n*/
}
/* Command lookup */
cmd = lookupCommand(argv[0]->ptr);
if (!cmd) {
redisLog(REDIS_WARNING,"Unknown command '%s' reading the append only file", (char*)argv[0]->ptr);
exit(1);
}
/* Run the command in the context of a fake client */
fakeClient->argc = argc;
fakeClient->argv = argv;
cmd->proc(fakeClient);//执行命令
/* The fake client should not have a reply */