本篇主要讲的是 AOF 持久化，了解 AOF 的数据组织方式和运作机制。redis 主要在 aof.c 中实现 AOF 的操作。

数据结构 rio

redis AOF 持久化同样借助了 struct rio. 详细内容在《深入剖析 redis RDB 持久化策略》中有介绍。

AOF 数据组织方式

假设 redis 内存有「name:Jhon」的键值对，那么进行 AOF 持久化后，AOF 文件有如下内容：

*2     # 2个参数
$6     # 第一个参数长度为 6
SELECT     # 第一个参数
$1     # 第二参数长度为 1
8     # 第二参数
*3     # 3个参数
$3     # 第一个参数长度为 4
SET     # 第一个参数
$4     # 第二参数长度为 4
name     # 第二个参数
$4     # 第三个参数长度为 4
Jhon     # 第二参数长度为 4

所以对上面的内容进行恢复，能得到熟悉的一条 redis 命令：SELECT 8;SET name Jhon.
可以想象的是，redis 遍历内存数据集中的每个 key-value 对，依次写入磁盘中；redis 启动的时候，从 AOF 文件中读取数据，恢复数据。

AOF 持久化运作机制

和 redis RDB 持久化运作机制不同，redis AOF 有后台执行和边服务边备份两种方式。

1）AOF 后台执行的方式和 RDB 有类似的地方，fork 一个子进程，主进程仍进行服务，子进程执行 AOF 持久化，数据被 dump 到磁盘上。与 RDB 不同的是，后台子进程持久化过程中，主进程会记录期间的所有数据变更（主进程还在服务），并存储在 server.aof_rewrite_buf_blocks 中；后台子进程结束后，redis 更新缓存追加到 AOF 文件中，是 RDB 持久化所不具备的。

来说说更新缓存这个东西。redis 服务器产生数据变更的时候，譬如 set name Jhon，不仅仅会修改内存数据集，也会记录此更新（修改）操作，记录的方式就是上面所说的数据组织方式。

更新缓存可以存储在 server.aof_buf 中，你可以把它理解为一个小型临时中转站，所有累积的更新缓存都会先放入这里，它会在特定时机写入文件或者插入到 server.aof_rewrite_buf_blocks 下链表（下面会详述）；server.aof_buf 中的数据在 propagrate() 添加，在涉及数据更新的地方都会调用 propagrate() 以累积变更。更新缓存也可以存储在 server.aof_rewrite_buf_blocks，这是一个元素类型为 struct aofrwblock 的链表，你可以把它理解为一个仓库，当后台有 AOF 子进程的时候，会将累积的更新缓存（在 server.aof_buf 中）插入到链表中，而当 AOF 子进程结束，它会被整个写入到文件。两者是有关联的。

下面是后台执行的主要代码：

// 启动后台子进程，执行 AOF 持久化操作。bgrewriteaofCommand()，startAppendOnly()，serverCron() 中会调用此函数
/* This is how rewriting of the append only file in background works:
*
* 1) The user calls BGREWRITEAOF
* 2) Redis calls this function, that forks():
*    2a) the child rewrite the append only file in a temp file.
*    2b) the parent accumulates differences in server.aof_rewrite_buf.
* 3) When the child finished '2a' exists.
* 4) The parent will trap the exit code, if it's OK, will append the
*    data accumulated into server.aof_rewrite_buf into the temp file, and
*    finally will rename(2) the temp file in the actual file name.
*    The the new file is reopened as the new append only file. Profit!
*/
int rewriteAppendOnlyFileBackground(void) {pid_t childpid;long long start;// 已经有正在执行备份的子进程if (server.aof_child_pid != -1) return REDIS_ERR;start = ustime();if ((childpid = fork()) == 0) {char tmpfile[256];// 子进程/* Child */// 关闭监听closeListeningSockets(0);// 设置进程 titleredisSetProcTitle("redis-aof-rewrite");// 临时文件名snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof", (int) getpid());// 脏数据，其实就是子进程所消耗的内存大小if (rewriteAppendOnlyFile(tmpfile) == REDIS_OK) {// 获取脏数据大小size_t private_dirty = zmalloc_get_private_dirty();// 记录脏数据if (private_dirty) {redisLog(REDIS_NOTICE,"AOF rewrite: %zu MB of memory used by copy-on-write",private_dirty/(1024*1024));}exitFromChild(0);} else {exitFromChild(1);}} else {/* Parent */server.stat_fork_time = ustime()-start;if (childpid == -1) {redisLog(REDIS_WARNING,"Can't rewrite append only file in background: fork: %s",strerror(errno));return REDIS_ERR;}redisLog(REDIS_NOTICE,"Background append only file rewriting started by pid %d",childpid);// AOF 已经开始执行，取消 AOF 计划server.aof_rewrite_scheduled = 0;// AOF 最近一次执行的起始时间server.aof_rewrite_time_start = time(NULL);// 子进程 IDserver.aof_child_pid = childpid;updateDictResizePolicy();// 因为更新缓存都将写入文件，要强制产生选择数据集的指令 SELECT ，以防出现数据合并错误。/* We set appendseldb to -1 in order to force the next call to the* feedAppendOnlyFile() to issue a SELECT command, so the differences* accumulated by the parent into server.aof_rewrite_buf will start* with a SELECT statement and it will be safe to merge. */server.aof_selected_db = -1;replicationScriptCacheFlush();return REDIS_OK;}return REDIS_OK; /* unreached */
}// AOF 持久化主函数。只在 rewriteAppendOnlyFileBackground() 中会调用此函数
/* Write a sequence of commands able to fully rebuild the dataset into
* "filename". Used both by REWRITEAOF and BGREWRITEAOF.
*
* In order to minimize the number of commands needed in the rewritten
* log Redis uses variadic commands when possible, such as RPUSH, SADD
* and ZADD. However at max REDIS_AOF_REWRITE_ITEMS_PER_CMD items per time
* are inserted using a single command. */
int rewriteAppendOnlyFile(char *filename) {dictIterator *di = NULL;dictEntry *de;rio aof;FILE *fp;char tmpfile[256];int j;long long now = mstime();/* Note that we have to use a different temp name here compared to the* one used by rewriteAppendOnlyFileBackground() function. */snprintf(tmpfile,256,"temp-rewriteaof-%d.aof", (int) getpid());// 打开文件fp = fopen(tmpfile,"w");if (!fp) {redisLog(REDIS_WARNING, "Opening the temp file for AOF rewrite in rewriteAppendOnlyFile(): %s", strerror(errno));return REDIS_ERR;}// 初始化 rio 结构体rioInitWithFile(&aof,fp);// 如果设置了自动备份参数，将进行设置if (server.aof_rewrite_incremental_fsync)rioSetAutoSync(&aof,REDIS_AOF_AUTOSYNC_BYTES);// 备份每一个数据集for (j = 0; j < server.dbnum; j++) {char selectcmd[] = "*2\r\n$6\r\nSELECT\r\n";redisDb *db = server.db+j;dict *d = db->dict;if (dictSize(d) == 0) continue;// 获取数据集的迭代器di = dictGetSafeIterator(d);if (!di) {fclose(fp);return REDIS_ERR;}// 写入 AOF 操作码/* SELECT the new DB */if (rioWrite(&aof,selectcmd,sizeof(selectcmd)-1) == 0) goto werr;// 写入数据集序号if (rioWriteBulkLongLong(&aof,j) == 0) goto werr;// 写入数据集中每一个数据项/* Iterate this DB writing every entry */while((de = dictNext(di)) != NULL) {sds keystr;robj key, *o;long long expiretime;keystr = dictGetKey(de);o = dictGetVal(de);// 将 keystr 封装在 robj 里initStaticStringObject(key,keystr);// 获取过期时间expiretime = getExpire(db,&key);// 如果已经过期，放弃存储/* If this key is already expired skip it */if (expiretime != -1 && expiretime < now) continue;// 写入键值对应的写操作/* Save the key and associated value */if (o->type == REDIS_STRING) {/* Emit a SET command */char cmd[]="*3\r\n$3\r\nSET\r\n";if (rioWrite(&aof,cmd,sizeof(cmd)-1) == 0) goto werr;/* Key and value */if (rioWriteBulkObject(&aof,&key) == 0) goto werr;if (rioWriteBulkObject(&aof,o) == 0) goto werr;} else if (o->type == REDIS_LIST) {if (rewriteListObject(&aof,&key,o) == 0) goto werr;} else if (o->type == REDIS_SET) {if (rewriteSetObject(&aof,&key,o) == 0) goto werr;} else if (o->type == REDIS_ZSET) {if (rewriteSortedSetObject(&aof,&key,o) == 0) goto werr;} else if (o->type == REDIS_HASH) {if (rewriteHashObject(&aof,&key,o) == 0) goto werr;} else {redisPanic("Unknown object type");}// 写入过期时间/* Save the expire time */if (expiretime != -1) {char cmd[]="*3\r\n$9\r\nPEXPIREAT\r\n";if (rioWrite(&aof,cmd,sizeof(cmd)-1) == 0) goto werr;if (rioWriteBulkObject(&aof,&key) == 0) goto werr;if (rioWriteBulkLongLong(&aof,expiretime) == 0) goto werr;}}// 释放迭代器dictReleaseIterator(di);}// 写入磁盘/* Make sure data will not remain on the OS's output buffers */fflush(fp);aof_fsync(fileno(fp));fclose(fp);// 重写文件名/* Use RENAME to make sure the DB file is changed atomically only* if the generate DB file is ok. */if (rename(tmpfile,filename) == -1) {redisLog(REDIS_WARNING,"Error moving temp append only file on the final destination: %s", strerror(errno));unlink(tmpfile);return REDIS_ERR;}redisLog(REDIS_NOTICE,"SYNC append only file rewrite performed");return REDIS_OK;werr:// 清理工作fclose(fp);unlink(tmpfile);redisLog(REDIS_WARNING,"Write error writing append only file on disk: %s", strerror(errno));if (di) dictReleaseIterator(di);return REDIS_ERR;
}// 后台子进程结束后，redis 更新缓存 server.aof_rewrite_buf_blocks 追加到 AOF 文件中
// 在 AOF 持久化结束后会执行这个函数， backgroundRewriteDoneHandler() 主要工作是将 server.aof_rewrite_buf_blocks，即 AOF 缓存写入文件
/* A background append only file rewriting (BGREWRITEAOF) terminated its work.* Handle this. */
void backgroundRewriteDoneHandler(int exitcode, int bysignal) {......// 将 AOF 缓存 server.aof_rewrite_buf_blocks 的 AOF 写入磁盘if (aofRewriteBufferWrite(newfd) == -1) {redisLog(REDIS_WARNING,"Error trying to flush the parent diff to the rewritten AOF: %s", strerror(errno));close(newfd);goto cleanup;}......
}// 将累积的更新缓存 server.aof_rewrite_buf_blocks 同步到磁盘
/* Write the buffer (possibly composed of multiple blocks) into the specified
* fd. If no short write or any other error happens -1 is returned,
* otherwise the number of bytes written is returned. */
ssize_t aofRewriteBufferWrite(int fd) {listNode *ln;listIter li;ssize_t count = 0;listRewind(server.aof_rewrite_buf_blocks,&li);while((ln = listNext(&li))) {aofrwblock *block = listNodeValue(ln);ssize_t nwritten;if (block->used) {nwritten = write(fd,block->buf,block->used);if (nwritten != block->used) {if (nwritten == 0) errno = EIO;return -1;}count += nwritten;}}return count;
}

2）边服务边备份的方式，即 redis 服务器会把所有的数据变更存储在 server.aof_buf 中，并在特定时机将更新缓存写入预设定的文件（server.aof_filename）。特定时机有三种：

1. 进入事件循环之前
2. redis 服务器定时程序 serverCron() 中
3. 停止 AOF 策略的 stopAppendOnly() 中

redis 无非是不想服务器突然崩溃终止，导致过多的数据丢失。redis 默认是每两秒钟进行一次边服务边备份，即隔两秒将累积的写入文件。

redis 为什么取消直接在本进程进行 AOF 持久化的方法？原因可能是产生一个 AOF 文件要比 RDB 文件消耗更多的时间；如果在当前进程执行 AOF 持久化，会占用服务进程（主进程）较多的时间，停止服务的时间也更长（？）

下面是边服务边备份的主要代码：

// 同步磁盘；将所有累积的更新 server.aof_buf 写入磁盘
/* Write the append only file buffer on disk.
*
* Since we are required to write the AOF before replying to the client,
* and the only way the client socket can get a write is entering when the
* the event loop, we accumulate all the AOF writes in a memory
* buffer and write it on disk using this function just before entering
* the event loop again.
*
* About the 'force' argument:
*
* When the fsync policy is set to 'everysec' we may delay the flush if there
* is still an fsync() going on in the background thread, since for instance
* on Linux write(2) will be blocked by the background fsync anyway.
* When this happens we remember that there is some aof buffer to be
* flushed ASAP, and will try to do that in the serverCron() function.
*
* However if force is set to 1 we'll write regardless of the background
* fsync. */
void flushAppendOnlyFile(int force) {ssize_t nwritten;int sync_in_progress = 0;// 无数据，无需同步到磁盘if (sdslen(server.aof_buf) == 0) return;// 创建线程任务，主要调用 fsync()if (server.aof_fsync == AOF_FSYNC_EVERYSEC)sync_in_progress = bioPendingJobsOfType(REDIS_BIO_AOF_FSYNC) != 0;// 如果没有设置强制同步的选项，可能不会立即进行同步if (server.aof_fsync == AOF_FSYNC_EVERYSEC && !force) {// 推迟执行 AOF/* With this append fsync policy we do background fsyncing.* If the fsync is still in progress we can try to delay* the write for a couple of seconds. */if (sync_in_progress) {if (server.aof_flush_postponed_start == 0) {// 设置延迟冲洗时间选项/* No previous write postponinig, remember that we are* postponing the flush and return. */server.aof_flush_postponed_start = server.unixtime; // /* Unix time sampled every cron cycle. */return;// 没有超过 2s，直接结束} else if (server.unixtime - server.aof_flush_postponed_start < 2) {/* We were already waiting for fsync to finish, but for less* than two seconds this is still ok. Postpone again. */return;}// 否则，要强制写入磁盘/* Otherwise fall trough, and go write since we can't wait* over two seconds. */server.aof_delayed_fsync++;redisLog(REDIS_NOTICE,"Asynchronous AOF fsync is taking too long (disk is busy?). Writing the AOF buffer without waiting for fsync to complete, this may slow down Redis.");}}// 取消延迟冲洗时间设置/* If you are following this code path, then we are going to write so* set reset the postponed flush sentinel to zero. */server.aof_flush_postponed_start = 0;/* We want to perform a single write. This should be guaranteed atomic* at least if the filesystem we are writing is a real physical one.* While this will save us against the server being killed I don't think* there is much to do about the whole server stopping for power problems* or alike */// AOF 文件已经打开了。将 server.aof_buf 中的所有缓存数据写入文件nwritten = write(server.aof_fd,server.aof_buf,sdslen(server.aof_buf));if (nwritten != (signed)sdslen(server.aof_buf)) {/* Ooops, we are in troubles. The best thing to do for now is* aborting instead of giving the illusion that everything is* working as expected. */if (nwritten == -1) {redisLog(REDIS_WARNING,"Exiting on error writing to the append-only file: %s",strerror(errno));} else {redisLog(REDIS_WARNING,"Exiting on short write while writing to ""the append-only file: %s (nwritten=%ld, ""expected=%ld)",strerror(errno),(long)nwritten,(long)sdslen(server.aof_buf));if (ftruncate(server.aof_fd, server.aof_current_size) == -1) {redisLog(REDIS_WARNING, "Could not remove short write ""from the append-only file.  Redis may refuse ""to load the AOF the next time it starts.  ""ftruncate: %s", strerror(errno));}}exit(1);}// 更新 AOF 文件的大小server.aof_current_size += nwritten;/*当 server.aof_buf 足够小,重新利用空间，防止频繁的内存分配。相反，当 server.aof_buf 占据大量的空间，采取的策略是释放空间，可见 redis 对内存很敏感。*//* Re-use AOF buffer when it is small enough. The maximum comes from the* arena size of 4k minus some overhead (but is otherwise arbitrary). */if ((sdslen(server.aof_buf)+sdsavail(server.aof_buf)) < 4000) {sdsclear(server.aof_buf);} else {sdsfree(server.aof_buf);server.aof_buf = sdsempty();}/* Don't fsync if no-appendfsync-on-rewrite is set to yes and there are* children doing I/O in the background. */if (server.aof_no_fsync_on_rewrite &&(server.aof_child_pid != -1 || server.rdb_child_pid != -1))return;// sync,写入磁盘/* Perform the fsync if needed. */if (server.aof_fsync == AOF_FSYNC_ALWAYS) {/* aof_fsync is defined as fdatasync() for Linux in order to avoid* flushing metadata. */aof_fsync(server.aof_fd); /* Let's try to get this data on the disk */server.aof_last_fsync = server.unixtime;} else if ((server.aof_fsync == AOF_FSYNC_EVERYSEC &&server.unixtime > server.aof_last_fsync)) {if (!sync_in_progress) aof_background_fsync(server.aof_fd);server.aof_last_fsync = server.unixtime;}
}

细说更新缓存

上面两次提到了「更新缓存」，它即是 redis 累积的数据变更。

更新缓存可以存储在 server.aof_buf 中，可以存储在 server.server.aof_rewrite_buf_blocks 连表中。他们的关系是：每一次数据变更记录都会写入 server.aof_buf 中，同时如果后台子进程在持久化，变更记录还会被写入 server.server.aof_rewrite_buf_blocks 中。server.aof_buf 会在特定时期写入指定文件，server.server.aof_rewrite_buf_blocks 会在后台持久化结束后追加到文件。

redis 源码中是这么实现的：propagrate()->feedAppendOnlyFile()->aofRewriteBufferAppend()

注释：feedAppendOnlyFile() 会把更新添加到 server.aof_buf；接下来会有一个判断，如果存在 AOF 子进程，则调用 aofRewriteBufferAppend() 将 server.aof_buf 中的所有数据插入到 server.aof_rewrite_buf_blocks 链表。

一副可以缓解视力疲劳的图片——AOF 持久化运作机制：

下面是主要的代码：

// 向 AOF 和从机发布数据更新
/* Propagate the specified command (in the context of the specified database id)
* to AOF and Slaves.
*
* flags are an xor between:
* + REDIS_PROPAGATE_NONE (no propagation of command at all)
* + REDIS_PROPAGATE_AOF (propagate into the AOF file if is enabled)
* + REDIS_PROPAGATE_REPL (propagate into the replication link)
*/
void propagate(struct redisCommand *cmd, int dbid, robj **argv, int argc,int flags)
{// AOF 策略需要打开，且设置 AOF 传播标记，将更新发布给本地文件if (server.aof_state != REDIS_AOF_OFF && flags & REDIS_PROPAGATE_AOF)feedAppendOnlyFile(cmd,dbid,argv,argc);// 设置了从机传播标记，将更新发布给从机if (flags & REDIS_PROPAGATE_REPL)replicationFeedSlaves(server.slaves,dbid,argv,argc);
}// 将数据更新记录到 AOF 缓存中
void feedAppendOnlyFile(struct redisCommand *cmd, int dictid, robj **argv, int argc) {sds buf = sdsempty();robj *tmpargv[3];/* The DB this command was targeting is not the same as the last command* we appendend. To issue a SELECT command is needed. */if (dictid != server.aof_selected_db) {char seldb[64];snprintf(seldb,sizeof(seldb),"%d",dictid);buf = sdscatprintf(buf,"*2\r\n$6\r\nSELECT\r\n$%lu\r\n%s\r\n",(unsigned long)strlen(seldb),seldb);server.aof_selected_db = dictid;}if (cmd->proc == expireCommand || cmd->proc == pexpireCommand ||cmd->proc == expireatCommand) {/* Translate EXPIRE/PEXPIRE/EXPIREAT into PEXPIREAT */buf = catAppendOnlyExpireAtCommand(buf,cmd,argv[1],argv[2]);} else if (cmd->proc == setexCommand || cmd->proc == psetexCommand) {/* Translate SETEX/PSETEX to SET and PEXPIREAT */tmpargv[0] = createStringObject("SET",3);tmpargv[1] = argv[1];tmpargv[2] = argv[3];buf = catAppendOnlyGenericCommand(buf,3,tmpargv);decrRefCount(tmpargv[0]);buf = catAppendOnlyExpireAtCommand(buf,cmd,argv[1],argv[2]);} else {/* All the other commands don't need translation or need the* same translation already operated in the command vector* for the replication itself. */buf = catAppendOnlyGenericCommand(buf,argc,argv);}// 将生成的 AOF 追加到 server.aof_buf 中。server.在下一次进入事件循环之前，aof_buf 中的内容将会写到磁盘上/* Append to the AOF buffer. This will be flushed on disk just before* of re-entering the event loop, so before the client will get a* positive reply about the operation performed. */if (server.aof_state == REDIS_AOF_ON)server.aof_buf = sdscatlen(server.aof_buf,buf,sdslen(buf));// 如果已经有 AOF 子进程运行，redis 采取的策略是累积子进程 AOF 备份的数据和内存中数据集的差异。 aofRewriteBufferAppend() 把 buf 的内容追加到 server.aof_rewrite_buf_blocks 数组中/* If a background append only file rewriting is in progress we want to* accumulate the differences between the child DB and the current one* in a buffer, so that when the child process will do its work we* can append the differences to the new append only file. */if (server.aof_child_pid != -1)aofRewriteBufferAppend((unsigned char*)buf,sdslen(buf));sdsfree(buf);
}// 将数据更新记录写入 server.aof_rewrite_buf_blocks，此函数只由 feedAppendOnlyFile() 调用
/* Append data to the AOF rewrite buffer, allocating new blocks if needed. */
void aofRewriteBufferAppend(unsigned char *s, unsigned long len) {// 尾插法listNode *ln = listLast(server.aof_rewrite_buf_blocks);aofrwblock *block = ln ? ln->value : NULL;while(len) {/* If we already got at least an allocated block, try appending* at least some piece into it. */if (block) {unsigned long thislen = (block->free < len) ? block->free : len;if (thislen) {  /* The current block is not already full. */memcpy(block->buf+block->used, s, thislen);block->used += thislen;block->free -= thislen;s += thislen;len -= thislen;}}if (len) { /* First block to allocate, or need another block. */int numblocks;// 创建新的节点，插到尾部block = zmalloc(sizeof(*block));block->free = AOF_RW_BUF_BLOCK_SIZE;block->used = 0;// 尾插法listAddNodeTail(server.aof_rewrite_buf_blocks,block);/* Log every time we cross more 10 or 100 blocks, respectively* as a notice or warning. */numblocks = listLength(server.aof_rewrite_buf_blocks);if (((numblocks+1) % 10) == 0) {int level = ((numblocks+1) % 100) == 0 ? REDIS_WARNING :REDIS_NOTICE;redisLog(level,"Background AOF buffer size: %lu MB",aofRewriteBufferSize()/(1024*1024));}}}
}

两种数据落地的方式，就是 AOF 的两个主线。因此，redis AOF 持久化机制有两条主线：后台执行和边服务边备份，抓住这两点就能理解 redis AOF 了。

这里有一个疑问，两条主线都会涉及文件的写：后台执行会写一个 AOF 文件，边服务边备份也会写一个，以哪个为准？

后台持久化的数据首先会被写入「temp-rewriteaof-bg-%d.aof」，其中「%d」是 AOF 子进程 id；待 AOF 子进程结束后，「temp-rewriteaof-bg-%d.aof」会被以追加的方式打开，继而写入 server.aof_rewrite_buf_blocks 中的更新缓存，最后「temp-rewriteaof-bg-%d.aof」文件被命名为 server.aof_filename，所以之前的名为 server.aof_filename 的文件会被删除，也就是说边服务边备份写入的文件会被删除。边服务边备份的数据会被一直写入到 server.aof_filename 文件中。

因此，确实会产生两个文件，但是最后都会变成 server.aof_filename 文件。

这里还有一个疑问，既然有了后台持久化，为什么还要边服务边备份？边服务边备份时间长了会产生数据冗余甚至备份过旧的数据，而后台持久化可以消除这些东西。看，这里是 redis 的双保险。

AOF 恢复过程

AOF 的数据恢复过程设计实在是棒极了，它模拟一个服务过程。redis 首先虚拟一个客户端，读取 AOF 文件恢复 redis 命令和参数；然后就像服务客户端一样执行命令相应的函数，从而恢复数据。这些过程主要在loadAppendOnlyFile() 中实现。

// 加载 AOF 文件，恢复数据
/* Replay the append log file. On error REDIS_OK is returned. On non fatal
* error (the append only file is zero-length) REDIS_ERR is returned. On
* fatal error an error message is logged and the program exists. */
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;// 文件大小不能为 0if (fp && redis_fstat(fileno(fp),&sb) != -1 && sb.st_size == 0) {server.aof_current_size = 0;fclose(fp);return REDIS_ERR;}if (fp == NULL) {redisLog(REDIS_WARNING,"Fatal error: can't open the append log file for reading: %s",strerror(errno));exit(1);}// 正在执行 AOF 加载操作，于是暂时禁止 AOF 的所有操作，以免混淆/* 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;// 虚拟出一个客户端，即 redisClientfakeClient = createFakeClient();startLoading(fp);while(1) {int argc, j;unsigned long len;robj **argv;char buf[128];sds argsds;struct redisCommand *cmd;// 每循环 1000 次，在恢复数据的同时，服务器也为客户端服务。aeProcessEvents() 会进入事件循环/* Serve the clients from time to time */if (!(loops++ % 1000)) {loadingProgress(ftello(fp));aeProcessEvents(server.el, AE_FILE_EVENTS|AE_DONT_WAIT);}// 可能 aof 文件到了结尾if (fgets(buf,sizeof(buf),fp) == NULL) {if (feof(fp))break;elsegoto readerr;}// 必须以“*”开头，格式不对，退出if (buf[0] != '*') goto fmterr;// 参数的个数argc = atoi(buf+1);// 参数个数错误if (argc < 1) goto fmterr;// 为参数分配空间argv = zmalloc(sizeof(robj*)*argc);// 依次读取参数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);argsds = sdsnewlen(NULL,len);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 */}// 找到相应的命令/* 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);}// 执行命令，模拟服务客户端请求的过程，从而写入数据/* Run the command in the context of a fake client */fakeClient->argc = argc;fakeClient->argv = argv;cmd->proc(fakeClient);/* The fake client should not have a reply */redisAssert(fakeClient->bufpos == 0 && listLength(fakeClient->reply) == 0);/* The fake client should never get blocked */redisAssert((fakeClient->flags & REDIS_BLOCKED) == 0);// 释放虚拟客户端空间/* Clean up. Command code may have changed argv/argc so we use the* argv/argc of the client instead of the local variables. */for (j = 0; j < fakeClient->argc; j++)decrRefCount(fakeClient->argv[j]);zfree(fakeClient->argv);}/* This point can only be reached when EOF is reached without errors.* If the client is in the middle of a MULTI/EXEC, log error and quit. */if (fakeClient->flags & REDIS_MULTI) goto readerr;// 清理工作fclose(fp);freeFakeClient(fakeClient);// 恢复旧的 AOF 状态server.aof_state = old_aof_state;stopLoading();// 记录最近 AOF 操作的文件大小aofUpdateCurrentSize();server.aof_rewrite_base_size = server.aof_current_size;return REDIS_OK;readerr:// 错误，清理工作if (feof(fp)) {redisLog(REDIS_WARNING,"Unexpected end of file reading the append only file");} else {redisLog(REDIS_WARNING,"Unrecoverable error reading the append only file: %s", strerror(errno));}exit(1);
fmterr:redisLog(REDIS_WARNING,"Bad file format reading the append only file: make a backup of your AOF file, then use ./redis-check-aof --fix <filename>");exit(1);
}

AOF 的适用场景

如果对数据比较关心，分秒必争，可以用 AOF 持久化，而且 AOF 文件很容易进行分析。

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捣乱 2014-3-26

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