rdb文件是redis實(shí)現(xiàn)持久化方式的一種，即通過save或bgsave操作，執(zhí)行數(shù)據(jù)備份，生成的.rdb后綴的數(shù)據(jù)文件。
save和bgsave都是調(diào)用rdbSave實(shí)現(xiàn)備份的，只不過save是阻塞式，bgsave是非阻塞式，通過fork子進(jìn)程執(zhí)行備份，主進(jìn)程可以繼續(xù)接收外部請(qǐng)求。源碼如下：
一、save方法
直接調(diào)用rdbsave()方法
void saveCommand(client *c) {
if (server.rdb_child_pid != -1) {
addReplyError(c,"Background save already in progress");
return;
}
rdbSaveInfo rsi, *rsiptr;
rsiptr = rdbPopulateSaveInfo(&rsi);
if (rdbSave(server.rdb_filename,rsiptr) == C_OK) {
addReply(c,shared.ok);
} else {
addReply(c,shared.err);
}
}
二、bgsave方法
調(diào)用的是rdbSaveBackground()方法
/* BGSAVE [SCHEDULE] */
void bgsaveCommand(client *c) {
int schedule = 0;
/* The SCHEDULE option changes the behavior of BGSAVE when an AOF rewrite
* is in progress. Instead of returning an error a BGSAVE gets scheduled. */
if (c->argc > 1) {
if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"schedule")) {
schedule = 1;
} else {
addReply(c,shared.syntaxerr);
return;
}
}
rdbSaveInfo rsi, *rsiptr;
rsiptr = rdbPopulateSaveInfo(&rsi);
if (server.rdb_child_pid != -1) {
addReplyError(c,"Background save already in progress");
} else if (server.aof_child_pid != -1) {
if (schedule) {
server.rdb_bgsave_scheduled = 1;
addReplyStatus(c,"Background saving scheduled");
} else {
addReplyError(c,
"An AOF log rewriting in progress: can't BGSAVE right now. "
"Use BGSAVE SCHEDULE in order to schedule a BGSAVE whenever "
"possible.");
}
} else if (rdbSaveBackground(server.rdb_filename,rsiptr) == C_OK) { #實(shí)際上調(diào)用的是rdbSaveBackground方法
addReplyStatus(c,"Background saving started");
} else {
addReply(c,shared.err);
}
}
三、rdbSaveBackground方法
int rdbSaveBackground(char *filename, rdbSaveInfo *rsi) {
pid_t childpid;
long long start;
if (server.aof_child_pid != -1 || server.rdb_child_pid != -1) return C_ERR;
server.dirty_before_bgsave = server.dirty;
server.lastbgsave_try = time(NULL);
openChildInfoPipe();
start = ustime();
if ((childpid = fork()) == 0) {
int retval;
/* Child */
closeListeningSockets(0);
redisSetProcTitle("redis-rdb-bgsave");
retval = rdbSave(filename,rsi); # 最終調(diào)用的還是rdbsave()方法，但是是在子進(jìn)程中調(diào)用的
if (retval == C_OK) {
size_t private_dirty = zmalloc_get_private_dirty(-1);
if (private_dirty) {
serverLog(LL_NOTICE,
"RDB: %zu MB of memory used by copy-on-write",
private_dirty/(1024*1024));
}
server.child_info_data.cow_size = private_dirty;
sendChildInfo(CHILD_INFO_TYPE_RDB);
}
exitFromChild((retval == C_OK) ? 0 : 1);
} else {
/* Parent */
server.stat_fork_time = ustime()-start;
server.stat_fork_rate = (double) zmalloc_used_memory() * 1000000 / server.stat_fork_time / (1024*1024*1024); /* GB per second. */
latencyAddSampleIfNeeded("fork",server.stat_fork_time/1000);
if (childpid == -1) {
closeChildInfoPipe();
server.lastbgsave_status = C_ERR;
serverLog(LL_WARNING,"Can't save in background: fork: %s",
strerror(errno));
return C_ERR;
}
serverLog(LL_NOTICE,"Background saving started by pid %d",childpid);
server.rdb_save_time_start = time(NULL);
server.rdb_child_pid = childpid;
server.rdb_child_type = RDB_CHILD_TYPE_DISK;
updateDictResizePolicy();
return C_OK;
}
return C_OK; /* unreached */
}
在了解rdb文件是怎么生成后，接下來就看看rdb文件內(nèi)容，rdb文件是二進(jìn)制格式的，直接打開是亂碼，可以使用命令 od -c xxx.rdb 查看
四、RDB文件內(nèi)容解析
本地先安裝redis吧（此處省略）
由于是之前安裝好的，此處執(zhí)行flushall命令情況redis數(shù)據(jù)庫
