http://blog.csdn.net/acceptedxukai/article/details/18136903
http://blog.csdn.net/acceptedxukai/article/details/18181563
本文所引用的源碼全部來自Redis2.8.2版本。
Redis AOF數據持久化機制的實現相關代碼是redis.c, redis.h, aof.c, bio.c, rio.c, config.c
在閱讀本文之前請先閱讀Redis數據持久化機制AOF原理分析之配置詳解文章，了解AOF相關參數的解析，文章鏈接
http://blog.csdn.net/acceptedxukai/article/details/18135219
轉載請注明，文章出自http://blog.csdn.net/acceptedxukai/article/details/18136903
下面將介紹AOF數據持久化機制的實現
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Server啟動加載AOF文件數據
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Server啟動加載AOF文件數據的執行步驟為:main() -> initServerConfig() -> loadServerConfig() -> initServer() -> loadDataFromDisk()。initServerConfig()主要為初始化默認的AOF參數配置；loadServerConfig()加載配置文件redis.conf中AOF的參數配置，覆蓋Server的默認AOF參數配置，如果配置appendonly on，那么AOF數據持久化功能將被激活，server.aof_state參數被設置為REDIS_AOF_ON；loadDataFromDisk()判斷server.aof_state == REDIS_AOF_ON，結果為True就調用loadAppendOnlyFile函數加載AOF文件中的數據，加載的方法就是讀取AOF文件中數據，由于AOF文件中存儲的數據與客戶端發送的請求格式相同完全符合Redis的通信協議，因此Server創建偽客戶端fakeClient，將解析后的AOF文件數據像客戶端請求一樣調用各種指令，cmd->proc(fakeClient)，將AOF文件中的數據重現到Redis Server數據庫中。
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??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首先判斷加載AOF文件是因為AOF文件中的數據要比RDB文件中的數據要新。
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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;????????????????????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)?{??????????redisLog(REDIS_WARNING,"Fatal?error:?can't?open?the?append?log?file?for?reading:?%s",strerror(errno));??????????exit(1);??????}???????????????server.aof_state?=?REDIS_AOF_OFF;????????fakeClient?=?createFakeClient();???????startLoading(fp);?????????while(1)?{??????????int?argc,?j;??????????unsigned?long?len;??????????robj?**argv;??????????char?buf[128];??????????sds?argsds;??????????struct?redisCommand?*cmd;????????????????????????????????if?(!(loops++?%?1000))?{??????????????loadingProgress(ftello(fp));??????????????aeProcessEvents(server.el,?AE_FILE_EVENTS|AE_DONT_WAIT);??????????}????????????????????if?(fgets(buf,sizeof(buf),fp)?==?NULL)?{??????????????if?(feof(fp))??????????????????break;??????????????else??????????????????goto?readerr;??????????}????????????????????if?(buf[0]?!=?'*')?goto?fmterr;??????????argc?=?atoi(buf+1);??????????if?(argc?<?1)?goto?fmterr;????????????argv?=?zmalloc(sizeof(robj*)*argc);??????????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;???????????}??????????????????????cmd?=?lookupCommand(argv[0]->ptr);??????????if?(!cmd)?{??????????????redisLog(REDIS_WARNING,"Unknown?command?'%s'?reading?the?append?only?file",?(char*)argv[0]->ptr);??????????????exit(1);??????????}????????????????????fakeClient->argc?=?argc;??????????fakeClient->argv?=?argv;??????????cmd->proc(fakeClient);??????????????????????redisAssert(fakeClient->bufpos?==?0?&&?listLength(fakeClient->reply)?==?0);????????????????????redisAssert((fakeClient->flags?&?REDIS_BLOCKED)?==?0);???????????????????????for?(j?=?0;?j?<?fakeClient->argc;?j++)??????????????decrRefCount(fakeClient->argv[j]);??????????zfree(fakeClient->argv);??????}???????????????if?(fakeClient->flags?&?REDIS_MULTI)?goto?readerr;????????fclose(fp);??????freeFakeClient(fakeClient);??????server.aof_state?=?old_aof_state;??????stopLoading();??????aofUpdateCurrentSize();???????server.aof_rewrite_base_size?=?server.aof_current_size;??????return?REDIS_OK;??????…………??}?? 在前面一篇關于AOF參數配置的博客遺留了一個問題，server.aof_current_size參數的初始化，下面解決這個疑問。
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void?aofUpdateCurrentSize(void)?{??????struct?redis_stat?sb;????????if?(redis_fstat(server.aof_fd,&sb)?==?-1)?{??????????redisLog(REDIS_WARNING,"Unable?to?obtain?the?AOF?file?length.?stat:?%s",??????????????strerror(errno));??????}?else?{??????????server.aof_current_size?=?sb.st_size;??????}??}?? redis_fstat是作者對Linux中fstat64函數的重命名，該還是就是獲取文件相關的參數信息，具體可以Google之，sb.st_size就是當前AOF文件的大小。這里需要知道server.aof_fd即AOF文件描述符，該參數的初始化在initServer()函數中
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??????if?(server.aof_state?==?REDIS_AOF_ON)?{??????????server.aof_fd?=?open(server.aof_filename,O_WRONLY|O_APPEND|O_CREAT,0644);??????????if?(server.aof_fd?==?-1)?{??????????????redisLog(REDIS_WARNING,?"Can't?open?the?append-only?file:?%s",strerror(errno));??????????????exit(1);??????????}??????}?? ?
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至此，Redis Server啟動加載硬盤中AOF文件數據的操作就成功結束了。
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Server數據庫產生新數據如何持久化到硬盤
當客戶端執行Set等修改數據庫中字段的指令時就會造成Server數據庫中數據被修改，這些修改的數據應該被實時更新到AOF文件中，并且也要按照一定的fsync機制刷新到硬盤中，保證數據不會丟失。
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在上一篇博客中，提到了三種fsync方式:appendfsync always,?appendfsync everysec,?appendfsync no. 具體體現在server.aof_fsync參數中。
首先看當客戶端請求的指令造成數據被修改，Redis是如何將修改數據的指令添加到server.aof_buf中的。
call() ->?propagate() ->?feedAppendOnlyFile()，call()函數判斷執行指令后是否造成數據被修改。
feedAppendOnlyFile函數首先會判斷Server是否開啟了AOF，如果開啟AOF，那么根據Redis通訊協議將修改數據的指令重現成請求的字符串，注意在超時設置的處理方式，接著將字符串append到server.aof_buf中即可。該函數最后兩行代碼需要注意，這才是重點，如果server.aof_child_pid != -1那么表明此時Server正在重寫rewrite AOF文件，需要將被修改的數據追加到server.aof_rewrite_buf_blocks鏈表中，等待rewrite結束后，追加到AOF文件中。具體見下面代碼的注釋。
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?????????void?propagate(struct?redisCommand?*cmd,?int?dbid,?robj?**argv,?int?argc,?????????????????int?flags)??{????????????if?(server.aof_state?!=?REDIS_AOF_OFF?&&?flags?&?REDIS_PROPAGATE_AOF)??????????feedAppendOnlyFile(cmd,dbid,argv,argc);??????if?(flags?&?REDIS_PROPAGATE_REPL)??????????replicationFeedSlaves(server.slaves,dbid,argv,argc);??}?? [cpp]?view plaincopyprint?
??void?feedAppendOnlyFile(struct?redisCommand?*cmd,?int?dictid,?robj?**argv,?int?argc)?{??????sds?buf?=?sdsempty();??????robj?*tmpargv[3];?????????????????????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)?{????????????????????buf?=?catAppendOnlyExpireAtCommand(buf,cmd,argv[1],argv[2]);??????}??????else?if?(cmd->proc?==?setexCommand?||?cmd->proc?==?psetexCommand)?{????????????????????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?{??????????????????????buf?=?catAppendOnlyGenericCommand(buf,argc,argv);??????}??????????????????????if?(server.aof_state?==?REDIS_AOF_ON)??????????server.aof_buf?=?sdscatlen(server.aof_buf,buf,sdslen(buf));???????????????????????????????????????????????if?(server.aof_child_pid?!=?-1)??????????aofRewriteBufferAppend((unsigned?char*)buf,sdslen(buf));??????????????????????sdsfree(buf);??}?? ?
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Server在每次事件循環之前會調用一次beforeSleep函數，下面看看這個函數做了什么工作？
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????void?beforeSleep(struct?aeEventLoop?*eventLoop)?{??????REDIS_NOTUSED(eventLoop);??????listNode?*ln;??????redisClient?*c;???????????????if?(server.active_expire_enabled?&&?server.masterhost?==?NULL)??????????activeExpireCycle(ACTIVE_EXPIRE_CYCLE_FAST);??????????????while?(listLength(server.unblocked_clients))?{??????????ln?=?listFirst(server.unblocked_clients);??????????redisAssert(ln?!=?NULL);??????????c?=?ln->value;??????????listDelNode(server.unblocked_clients,ln);??????????c->flags?&=?~REDIS_UNBLOCKED;????????????????????????????????if?(c->querybuf?&&?sdslen(c->querybuf)?>?0)?{??????????????server.current_client?=?c;??????????????processInputBuffer(c);??????????????server.current_client?=?NULL;??????????}??????}????????????????????flushAppendOnlyFile(0);??}?? 通過上面的代碼及注釋可以發現，beforeSleep函數做了三件事：1、處理過期鍵，2、處理阻塞期間的客戶端請求，3、將server.aof_buf中的數據追加到AOF文件中并fsync刷新到硬盤上，flushAppendOnlyFile函數給定了一個參數force，表示是否強制寫入AOF文件，0表示非強制即支持延遲寫，1表示強制寫入。
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void?flushAppendOnlyFile(int?force)?{??????ssize_t?nwritten;??????int?sync_in_progress?=?0;??????if?(sdslen(server.aof_buf)?==?0)?return;????????????if?(server.aof_fsync?==?AOF_FSYNC_EVERYSEC)??????????sync_in_progress?=?bioPendingJobsOfType(REDIS_BIO_AOF_FSYNC)?!=?0;??????????????if?(server.aof_fsync?==?AOF_FSYNC_EVERYSEC?&&?!force)?{????????????????????????????????if?(sync_in_progress)?{????????????????????????????if?(server.aof_flush_postponed_start?==?0)?{?????????????????????????????????????server.aof_flush_postponed_start?=?server.unixtime;??????????????????return;??????????????}?else?if?(server.unixtime?-?server.aof_flush_postponed_start?<?2)?{???????????????????????????????????????????????????????return;??????????????}?????????????????????????????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.");??????????}??????}?????????????server.aof_flush_postponed_start?=?0;????????????????????????nwritten?=?write(server.aof_fd,server.aof_buf,sdslen(server.aof_buf));??????if?(nwritten?!=?(signed)sdslen(server.aof_buf))?{??????????????????????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);??????}??????server.aof_current_size?+=?nwritten;?????????????????????if?((sdslen(server.aof_buf)+sdsavail(server.aof_buf))?<?4000)?{??????????sdsclear(server.aof_buf);??????}?else?{??????????sdsfree(server.aof_buf);??????????server.aof_buf?=?sdsempty();??????}???????????????????????????if?(server.aof_no_fsync_on_rewrite?&&??????????(server.aof_child_pid?!=?-1?||?server.rdb_child_pid?!=?-1))??????????????return;??????????????if?(server.aof_fsync?==?AOF_FSYNC_ALWAYS)?{?????????????????????aof_fsync(server.aof_fd);???????????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;??????}??}?? 上述代碼中請關注server.aof_fsync參數，即設置Redis fsync AOF文件到硬盤的策略，如果設置為AOF_FSYNC_ALWAYS，那么直接在主進程中fsync，如果設置為AOF_FSYNC_EVERYSEC，那么放入后臺線程中fsync，后臺線程的代碼在bio.c中。
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小結
文章寫到這，已經解決的了Redis Server啟動加載AOF文件和如何將客戶端請求產生的新的數據追加到AOF文件中，對于追加數據到AOF文件中，根據fsync的配置策略如何將寫入到AOF文件中的新數據刷新到硬盤中，直接在主進程中fsync或是在后臺線程fsync。
至此，AOF數據持久化還剩下如何rewrite AOF，接受客戶端發送的BGREWRITEAOF請求，此部分內容待下篇博客中解析。
感謝此篇博客給我在理解Redis AOF數據持久化方面的巨大幫助，http://chenzhenianqing.cn/articles/786.html
本人Redis-2.8.2的源碼注釋已經放到Github中，有需要的讀者可以下載，我也會在后續的時間中更新，https://github.com/xkeyideal/annotated-redis-2.8.2
本人不怎么會使用Git，望有人能教我一下。
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本文所引用的源碼全部來自Redis2.8.2版本。
Redis AOF數據持久化機制的實現相關代碼是redis.c, redis.h, aof.c, bio.c, rio.c, config.c
在閱讀本文之前請先閱讀Redis數據持久化機制AOF原理分析之配置詳解文章，了解AOF相關參數的解析，文章鏈接
http://blog.csdn.net/acceptedxukai/article/details/18135219
接著上一篇文章，本文將介紹Redis是如何實現AOF rewrite的。
轉載請注明，文章出自http://blog.csdn.net/acceptedxukai/article/details/18181563
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AOF rewrite的觸發機制
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如果Redis只是將客戶端修改數據庫的指令重現存儲在AOF文件中，那么AOF文件的大小會不斷的增加，因為AOF文件只是簡單的重現存儲了客戶端的指令，而并沒有進行合并。對于該問題最簡單的處理方式，即當AOF文件滿足一定條件時就對AOF進行rewrite，rewrite是根據當前內存數據庫中的數據進行遍歷寫到一個臨時的AOF文件，待寫完后替換掉原來的AOF文件即可。
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Redis觸發AOF rewrite機制有三種：
1、Redis Server接收到客戶端發送的BGREWRITEAOF指令請求，如果當前AOF/RDB數據持久化沒有在執行，那么執行，反之，等當前AOF/RDB數據持久化結束后執行AOF rewrite
2、在Redis配置文件redis.conf中，用戶設置了auto-aof-rewrite-percentage和auto-aof-rewrite-min-size參數，并且當前AOF文件大小server.aof_current_size大于auto-aof-rewrite-min-size(server.aof_rewrite_min_size)，同時AOF文件大小的增長率大于auto-aof-rewrite-percentage(server.aof_rewrite_perc)時，會自動觸發AOF rewrite
3、用戶設置“config set appendonly yes”開啟AOF的時，調用startAppendOnly函數會觸發rewrite
下面分別介紹上述三種機制的處理.
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接收到BGREWRITEAOF指令
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<span?style="font-size:12px;">void?bgrewriteaofCommand(redisClient?*c)?{????????????if?(server.aof_child_pid?!=?-1)?{??????????addReplyError(c,"Background?append?only?file?rewriting?already?in?progress");??????}?else?if?(server.rdb_child_pid?!=?-1)?{??????????????????????????????server.aof_rewrite_scheduled?=?1;??????????addReplyStatus(c,"Background?append?only?file?rewriting?scheduled");??????}?else?if?(rewriteAppendOnlyFileBackground()?==?REDIS_OK)?{????????????????????addReplyStatus(c,"Background?append?only?file?rewriting?started");??????}?else?{??????????addReply(c,shared.err);??????}??}</span>?? 當AOF rewrite請求被掛起時，在serverCron函數中，會處理。
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?????????????????????????if?(server.rdb_child_pid?==?-1?&&?server.aof_child_pid?==?-1?&&??????????server.aof_rewrite_scheduled)??????{??????????rewriteAppendOnlyFileBackground();??????}?? Server自動對AOF進行rewrite
在serverCron函數中會周期性判斷
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??????????????????????if?(server.rdb_child_pid?==?-1?&&???????????????server.aof_child_pid?==?-1?&&???????????????server.aof_rewrite_perc?&&???????????????server.aof_current_size?>?server.aof_rewrite_min_size)???????????{??????????????long?long?base?=?server.aof_rewrite_base_size????????????????????????????????server.aof_rewrite_base_size?:?1;??????????????long?long?growth?=?(server.aof_current_size*100/base)?-?100;??????????????if?(growth?>=?server.aof_rewrite_perc)?{??????????????????redisLog(REDIS_NOTICE,"Starting?automatic?rewriting?of?AOF?on?%lld%%?growth",growth);??????????????????rewriteAppendOnlyFileBackground();??????????????}???????????}?? config set appendonly yes
當客戶端發送該指令時，config.c中的configSetCommand函數會做出響應，startAppendOnly函數會執行AOF rewrite
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if?(!strcasecmp(c->argv[2]->ptr,"appendonly"))?{??????int?enable?=?yesnotoi(o->ptr);????????if?(enable?==?-1)?goto?badfmt;??????if?(enable?==?0?&&?server.aof_state?!=?REDIS_AOF_OFF)?{??????????stopAppendOnly();??????}?else?if?(enable?&&?server.aof_state?==?REDIS_AOF_OFF)?{??????????if?(startAppendOnly()?==?REDIS_ERR)?{??????????????addReplyError(c,??????????????????"Unable?to?turn?on?AOF.?Check?server?logs.");??????????????return;??????????}??????}??}?? [cpp]?view plaincopyprint?
int?startAppendOnly(void)?{??????server.aof_last_fsync?=?server.unixtime;??????server.aof_fd?=?open(server.aof_filename,O_WRONLY|O_APPEND|O_CREAT,0644);??????redisAssert(server.aof_state?==?REDIS_AOF_OFF);??????if?(server.aof_fd?==?-1)?{??????????redisLog(REDIS_WARNING,"Redis?needs?to?enable?the?AOF?but?can't?open?the?append?only?file:?%s",strerror(errno));??????????return?REDIS_ERR;??????}??????if?(rewriteAppendOnlyFileBackground()?==?REDIS_ERR)?{??????????close(server.aof_fd);??????????redisLog(REDIS_WARNING,"Redis?needs?to?enable?the?AOF?but?can't?trigger?a?background?AOF?rewrite?operation.?Check?the?above?logs?for?more?info?about?the?error.");??????????return?REDIS_ERR;??????}?????????????server.aof_state?=?REDIS_AOF_WAIT_REWRITE;??????return?REDIS_OK;??}?? Redis AOF rewrite機制的實現
從上述分析可以看出rewrite的實現全部依靠rewriteAppendOnlyFileBackground函數，下面分析該函數，通過下面的代碼可以看出，Redis是fork出一個子進程來操作AOF rewrite，然后子進程調用rewriteAppendOnlyFile函數，將數據寫到一個臨時文件temp-rewriteaof-bg-%d.aof中。如果子進程完成會通過exit(0)函數通知父進程rewrite結束，在serverCron函數中使用wait3函數接收子進程退出狀態，然后執行后續的AOF rewrite的收尾工作，后面將會分析。 父進程的工作主要包括清楚server.aof_rewrite_scheduled標志，記錄子進程IDserver.aof_child_pid = childpid，記錄rewrite的開始時間server.aof_rewrite_time_start = time(NULL)等。
[cpp]?view plaincopyprint?
int?rewriteAppendOnlyFileBackground(void)?{??????pid_t?childpid;??????long?long?start;??????????????if?(server.aof_child_pid?!=?-1)?return?REDIS_ERR;??????start?=?ustime();??????if?((childpid?=?fork())?==?0)?{??????????char?tmpfile[256];??????????????????????closeListeningSockets(0);??????????redisSetProcTitle("redis-aof-rewrite");??????????snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof",?(int)?getpid());??????????if?(rewriteAppendOnlyFile(tmpfile)?==?REDIS_OK)?{??????????????size_t?private_dirty?=?zmalloc_get_private_dirty();????????????????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?{????????????????????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);??????????server.aof_rewrite_scheduled?=?0;??????????server.aof_rewrite_time_start?=?time(NULL);??????????server.aof_child_pid?=?childpid;??????????updateDictResizePolicy();???????????????????????server.aof_selected_db?=?-1;??????????replicationScriptCacheFlush();??????????return?REDIS_OK;??????}??????return?REDIS_OK;???}?? 接下來介紹rewriteAppendOnlyFile函數，該函數的主要工作為：遍歷所有數據庫中的數據，將其寫入到臨時文件temp-rewriteaof-%d.aof中，寫入函數定義在rio.c中，比較簡單，然后將數據刷新到硬盤中，然后將文件名rename為其調用者給定的臨時文件名，注意仔細看代碼，這里并沒有修改為正式的AOF文件名。 在寫入文件時如果設置server.aof_rewrite_incremental_fsync參數，那么在rioWrite函數中fwrite部分數據就會將數據fsync到硬盤中，來保證數據的正確性。
[cpp]?view plaincopyprint?
int?rewriteAppendOnlyFile(char?*filename)?{??????dictIterator?*di?=?NULL;??????dictEntry?*de;??????rio?aof;??????FILE?*fp;??????char?tmpfile[256];??????int?j;??????long?long?now?=?mstime();???????????????snprintf(tmpfile,256,"temp-rewriteaof-%d.aof",?(int)?getpid());??????fp?=?fopen(tmpfile,"w");??????if?(!fp)?{??????????redisLog(REDIS_WARNING,?"Opening?the?temp?file?for?AOF?rewrite?in?rewriteAppendOnlyFile():?%s",?strerror(errno));??????????return?REDIS_ERR;??????}????????rioInitWithFile(&aof,fp);?????????????if?(server.aof_rewrite_incremental_fsync)??????????rioSetAutoSync(&aof,REDIS_AOF_AUTOSYNC_BYTES);??????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;??????????di?=?dictGetSafeIterator(d);??????????if?(!di)?{??????????????fclose(fp);??????????????return?REDIS_ERR;??????????}??????????????????????if?(rioWrite(&aof,selectcmd,sizeof(selectcmd)-1)?==?0)?goto?werr;??????????if?(rioWriteBulkLongLong(&aof,j)?==?0)?goto?werr;??????????????????????while((de?=?dictNext(di))?!=?NULL)?{??????????????sds?keystr;??????????????robj?key,?*o;??????????????long?long?expiretime;????????????????keystr?=?dictGetKey(de);??????????????o?=?dictGetVal(de);??????????????initStaticStringObject(key,keystr);????????????????expiretime?=?getExpire(db,&key);??????????????????????????????if?(expiretime?!=?-1?&&?expiretime?<?now)?continue;??????????????????????????????if?(o->type?==?REDIS_STRING)?{????????????????????????????????????char?cmd[]="*3\r\n$3\r\nSET\r\n";??????????????????if?(rioWrite(&aof,cmd,sizeof(cmd)-1)?==?0)?goto?werr;????????????????????????????????????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");??????????????}????????????????????????????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;??????????????}??????????}??????????dictReleaseIterator(di);??????}??????????????fflush(fp);??????aof_fsync(fileno(fp));??????fclose(fp);???????????????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:??????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;??}?? AOF rewrite工作到這里已經結束一半，上一篇文章提到如果server.aof_state != REDIS_AOF_OFF，那么就會將客戶端請求指令修改的數據通過feedAppendOnlyFile函數追加到AOF文件中，那么此時AOF已經rewrite了，必須要處理此時出現的差異數據，記得在feedAppendOnlyFile函數中有這么一段代碼
[cpp]?view plaincopyprint?
if?(server.aof_child_pid?!=?-1)??????????aofRewriteBufferAppend((unsigned?char*)buf,sdslen(buf));?? 如果AOF rewrite正在進行，那么就將修改數據的指令字符串存儲到server.aof_rewrite_buf_blocks鏈表中，等待AOF rewrite子進程結束后處理，處理此部分數據的代碼在serverCron函數中。需要指出的是wait3函數我不了解，可能下面注釋會有點問題。
[cpp]?view plaincopyprint?
????if?(server.rdb_child_pid?!=?-1?||?server.aof_child_pid?!=?-1)?{??????int?statloc;??????pid_t?pid;????????if?((pid?=?wait3(&statloc,WNOHANG,NULL))?!=?0)?{??????????int?exitcode?=?WEXITSTATUS(statloc);??????????int?bysignal?=?0;????????????if?(WIFSIGNALED(statloc))?bysignal?=?WTERMSIG(statloc);????????????if?(pid?==?server.rdb_child_pid)?{??????????????backgroundSaveDoneHandler(exitcode,bysignal);??????????}?else?if?(pid?==?server.aof_child_pid)?{??????????????backgroundRewriteDoneHandler(exitcode,bysignal);??????????}?else?{??????????????redisLog(REDIS_WARNING,??????????????????"Warning,?detected?child?with?unmatched?pid:?%ld",??????????????????(long)pid);??????????}????????????????????updateDictResizePolicy();??????}??}?? 對于AOF rewrite期間出現的差異數據，Server通過backgroundSaveDoneHandler函數將server.aof_rewrite_buf_blocks鏈表中數據追加到新的AOF文件中。 backgroundSaveDoneHandler函數執行步驟：
1、通過判斷子進程的退出狀態，正確的退出狀態為exit(0)，即exitcode為0，bysignal我不清楚具體意義，如果退出狀態正確，backgroundSaveDoneHandler函數才會開始處理 2、通過對rewriteAppendOnlyFileBackground函數的分析，可以知道rewrite后的AOF臨時文件名為temp-rewriteaof-bg-%d.aof(%d=server.aof_child_pid)中，接著需要打開此臨時文件 3、調用aofRewriteBufferWrite函數將server.aof_rewrite_buf_blocks中差異數據寫到該臨時文件中 4、如果舊的AOF文件未打開，那么打開舊的AOF文件，將文件描述符賦值給臨時變量oldfd 5、將臨時的AOF文件名rename為正常的AOF文件名 6、如果舊的AOF文件未打開，那么此時只需要關閉新的AOF文件，此時的server.aof_rewrite_buf_blocks數據應該為空；如果舊的AOF是打開的，那么將server.aof_fd指向newfd,然后根據相應的fsync策略將數據刷新到硬盤上 7、調用aofUpdateCurrentSize函數統計AOF文件的大小，更新server.aof_rewrite_base_size，為serverCron中自動AOF rewrite做相應判斷 8、如果之前是REDIS_AOF_WAIT_REWRITE狀態，則設置server.aof_state為REDIS_AOF_ON，因為只有“config set appendonly yes”指令才會設置這個狀態，也就是需要寫完快照后，立即打開AOF；而BGREWRITEAOF不需要打開AOF 9、調用后臺線程去關閉舊的AOF文件 下面是backgroundSaveDoneHandler函數的注釋代碼
[cpp]?view plaincopyprint?
???void?backgroundRewriteDoneHandler(int?exitcode,?int?bysignal)?{??????if?(!bysignal?&&?exitcode?==?0)?{??????????int?newfd,?oldfd;??????????char?tmpfile[256];??????????long?long?now?=?ustime();????????????redisLog(REDIS_NOTICE,??????????????"Background?AOF?rewrite?terminated?with?success");???????????????????????snprintf(tmpfile,256,"temp-rewriteaof-bg-%d.aof",??????????????(int)server.aof_child_pid);??????????newfd?=?open(tmpfile,O_WRONLY|O_APPEND);??????????if?(newfd?==?-1)?{??????????????redisLog(REDIS_WARNING,??????????????????"Unable?to?open?the?temporary?AOF?produced?by?the?child:?%s",?strerror(errno));??????????????goto?cleanup;??????????}????????????????????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;??????????}????????????redisLog(REDIS_NOTICE,??????????????"Parent?diff?successfully?flushed?to?the?rewritten?AOF?(%lu?bytes)",?aofRewriteBufferSize());????????????????????????????????????????????????if?(server.aof_fd?==?-1)?{????????????????????????????????????????????????oldfd?=?open(server.aof_filename,O_RDONLY|O_NONBLOCK);??????????}?else?{????????????????????????????oldfd?=?-1;???????????}???????????????????????????????????????????if?(rename(tmpfile,server.aof_filename)?==?-1)?{??????????????redisLog(REDIS_WARNING,??????????????????"Error?trying?to?rename?the?temporary?AOF?file:?%s",?strerror(errno));??????????????close(newfd);??????????????if?(oldfd?!=?-1)?close(oldfd);??????????????goto?cleanup;??????????}????????????????????????????????????????if?(server.aof_fd?==?-1)?{?????????????????????????????close(newfd);??????????}?else?{????????????????????????????oldfd?=?server.aof_fd;????????????????????????????server.aof_fd?=?newfd;????????????????????????????if?(server.aof_fsync?==?AOF_FSYNC_ALWAYS)??????????????????aof_fsync(newfd);??????????????else?if?(server.aof_fsync?==?AOF_FSYNC_EVERYSEC)??????????????????aof_background_fsync(newfd);??????????????server.aof_selected_db?=?-1;???????????????aofUpdateCurrentSize();??????????????server.aof_rewrite_base_size?=?server.aof_current_size;?????????????????????????????????????????????sdsfree(server.aof_buf);??????????????server.aof_buf?=?sdsempty();??????????}????????????server.aof_lastbgrewrite_status?=?REDIS_OK;????????????redisLog(REDIS_NOTICE,?"Background?AOF?rewrite?finished?successfully");??????????????????????????????if?(server.aof_state?==?REDIS_AOF_WAIT_REWRITE)??????????????server.aof_state?=?REDIS_AOF_ON;????????????????????????????????if?(oldfd?!=?-1)?bioCreateBackgroundJob(REDIS_BIO_CLOSE_FILE,(void*)(long)oldfd,NULL,NULL);????????????redisLog(REDIS_VERBOSE,??????????????"Background?AOF?rewrite?signal?handler?took?%lldus",?ustime()-now);??????}?else?if?(!bysignal?&&?exitcode?!=?0)?{??????????server.aof_lastbgrewrite_status?=?REDIS_ERR;????????????redisLog(REDIS_WARNING,??????????????"Background?AOF?rewrite?terminated?with?error");??????}?else?{??????????server.aof_lastbgrewrite_status?=?REDIS_ERR;????????????redisLog(REDIS_WARNING,??????????????"Background?AOF?rewrite?terminated?by?signal?%d",?bysignal);??????}????cleanup:??????aofRewriteBufferReset();??????aofRemoveTempFile(server.aof_child_pid);??????server.aof_child_pid?=?-1;??????server.aof_rewrite_time_last?=?time(NULL)-server.aof_rewrite_time_start;??????server.aof_rewrite_time_start?=?-1;????????????if?(server.aof_state?==?REDIS_AOF_WAIT_REWRITE)??????????server.aof_rewrite_scheduled?=?1;??}?? 至此，AOF數據持久化已經全部結束了，剩下的就是一些細節的處理，以及一些Linux庫函數的理解，對于rename、unlink、wait3等庫函數的深入認識就去問Google吧。
小結
Redis AOF數據持久化的實現機制通過三篇文章基本上比較詳細的分析了，但這只是從代碼層面去看AOF，對于AOF持久化的優缺點網上有很多分析，Redis的官方網站也有英文介紹，Redis的數據持久化還有一種方法叫RDB，更多RDB的內容等下次再分析。 感謝此篇博客給我在理解Redis AOF數據持久化方面的巨大幫助，http://chenzhenianqing.cn/articles/786.html，此篇博客對AOF的分析十分的詳細。
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轉載于:https://www.cnblogs.com/davidwang456/p/3521182.html
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