Redis 源代码］7RDB Persistence-4 核心代码

rdbSave

/* Save the DB on disk. Return C_ERR on error, C_OK on success. */
int rdbSave(char *filename, rdbSaveInfo *rsi) {
    char tmpfile[256];
    char cwd[MAXPATHLEN]; /* Current working dir path for error messages. */
    FILE *fp = NULL;
    rio rdb;
    int error = 0;
	/*
	创建一个临时文件名 temp-<pid>.rdb，其中 <pid> 是当前进程的 PID。
	打开临时文件进行写操作。如果打开失败，记录错误日志并返回 C_ERR。
	*/
    snprintf(tmpfile,256,"temp-%d.rdb", (int) getpid());
    fp = fopen(tmpfile,"w");
    if (!fp) {
        char *cwdp = getcwd(cwd,MAXPATHLEN);
        serverLog(LL_WARNING,
            "Failed opening the RDB file %s (in server root dir %s) "
            "for saving: %s",
            filename,
            cwdp ? cwdp : "unknown",
            strerror(errno));
        return C_ERR;
    }
	/*
	初始化 RIO 结构体
	使用 rioInitWithFile 初始化 RIO（Redis I/O）结构体，使其与文件关联。
	调用 startSaving 函数开始保存过程，并传递标志 RDBFLAGS_NONE 表示没有特殊标志。
	*/
    rioInitWithFile(&rdb,fp);
    startSaving(RDBFLAGS_NONE);

    if (server.rdb_save_incremental_fsync)
        rioSetAutoSync(&rdb,REDIS_AUTOSYNC_BYTES);
	/*
	调用 rdbSaveRio 函数将数据写入 RIO 结构体。如果保存过程中出现错误，设置 errno 并跳转到 werr 标签。
	*/
    if (rdbSaveRio(&rdb,&error,RDBFLAGS_NONE,rsi) == C_ERR) {
        errno = error;
        goto werr;
    }

    /* Make sure data will not remain on the OS's output buffers */
    /*
    刷新文件缓冲区，确保所有数据都被写入文件。
	对文件描述符执行 fsync，确保数据被持久化到磁盘。
	关闭文件。如果任何一步失败，跳转到 werr 标签。
    
    */
    if (fflush(fp)) goto werr;
    if (fsync(fileno(fp))) goto werr;
    if (fclose(fp)) { fp = NULL; goto werr; }
    fp = NULL;
    
    /* Use RENAME to make sure the DB file is changed atomically only
     * if the generate DB file is ok. */
    //将临时文件重命名为最终的目标文件名。如果重命名失败，记录错误日志，删除临时文件，并返回 C_ERR。
    if (rename(tmpfile,filename) == -1) {
        char *cwdp = getcwd(cwd,MAXPATHLEN);
        serverLog(LL_WARNING,
            "Error moving temp DB file %s on the final "
            "destination %s (in server root dir %s): %s",
            tmpfile,
            filename,
            cwdp ? cwdp : "unknown",
            strerror(errno));
        unlink(tmpfile);
        stopSaving(0);
        return C_ERR;
    }

    serverLog(LL_NOTICE,"DB saved on disk");
    server.dirty = 0;
    server.lastsave = time(NULL);
    server.lastbgsave_status = C_OK;
    stopSaving(1);
    return C_OK;

werr:
    serverLog(LL_WARNING,"Write error saving DB on disk: %s", strerror(errno));
    if (fp) fclose(fp);
    unlink(tmpfile);
    stopSaving(0);
    return C_ERR;
}

/*
rdb：指向 rio 结构体的指针，用于写入数据。
error：指向整数的指针，用于存储错误代码。
rdbflags：标志位，包含一些额外的信息（如是否为 AOF 重写前言）。
rsi：指向 rdbSaveInfo 结构体的指针，包含一些额外的信息（如复制偏移量等）。
*/
int rdbSaveRio(rio *rdb, int *error, int rdbflags, rdbSaveInfo *rsi) {
    dictIterator *di = NULL;
    dictEntry *de;
    char magic[10];
    uint64_t cksum;
    size_t processed = 0;
    int j;
    long key_count = 0;
    long long info_updated_time = 0;
    char *pname = (rdbflags & RDBFLAGS_AOF_PREAMBLE) ? "AOF rewrite" :  "RDB";

    if (server.rdb_checksum)
        rdb->update_cksum = rioGenericUpdateChecksum;
    snprintf(magic,sizeof(magic),"REDIS%04d",RDB_VERSION);
    if (rdbWriteRaw(rdb,magic,9) == -1) goto werr;
    if (rdbSaveInfoAuxFields(rdb,rdbflags,rsi) == -1) goto werr;
    if (rdbSaveModulesAux(rdb, REDISMODULE_AUX_BEFORE_RDB) == -1) goto werr;

    for (j = 0; j < server.dbnum; j++) {
        redisDb *db = server.db+j;
        dict *d = db->dict;
        if (dictSize(d) == 0) continue;
        di = dictGetSafeIterator(d);

        /* Write the SELECT DB opcode */
        if (rdbSaveType(rdb,RDB_OPCODE_SELECTDB) == -1) goto werr;
        if (rdbSaveLen(rdb,j) == -1) goto werr;

        /* Write the RESIZE DB opcode. */
        uint64_t db_size, expires_size;
        db_size = dictSize(db->dict);
        expires_size = dictSize(db->expires);
        if (rdbSaveType(rdb,RDB_OPCODE_RESIZEDB) == -1) goto werr;
        if (rdbSaveLen(rdb,db_size) == -1) goto werr;
        if (rdbSaveLen(rdb,expires_size) == -1) goto werr;

        /* Iterate this DB writing every entry */
        while((de = dictNext(di)) != NULL) {
            sds keystr = dictGetKey(de);
            robj key, *o = dictGetVal(de);
            long long expire;

            initStaticStringObject(key,keystr);
            expire = getExpire(db,&key);
            if (rdbSaveKeyValuePair(rdb,&key,o,expire) == -1) goto werr;

            /* When this RDB is produced as part of an AOF rewrite, move
             * accumulated diff from parent to child while rewriting in
             * order to have a smaller final write. */
            if (rdbflags & RDBFLAGS_AOF_PREAMBLE &&
                rdb->processed_bytes > processed+AOF_READ_DIFF_INTERVAL_BYTES)
            {
                processed = rdb->processed_bytes;
                aofReadDiffFromParent();
            }

            /* Update child info every 1 second (approximately).
             * in order to avoid calling mstime() on each iteration, we will
             * check the diff every 1024 keys */
            if ((key_count++ & 1023) == 0) {
                long long now = mstime();
                if (now - info_updated_time >= 1000) {
                    sendChildInfo(CHILD_INFO_TYPE_CURRENT_INFO, key_count, pname);
                    info_updated_time = now;
                }
            }
        }
        dictReleaseIterator(di);
        di = NULL; /* So that we don't release it again on error. */
    }

    /* If we are storing the replication information on disk, persist
     * the script cache as well: on successful PSYNC after a restart, we need
     * to be able to process any EVALSHA inside the replication backlog the
     * master will send us. */
    if (rsi && dictSize(server.lua_scripts)) {
        di = dictGetIterator(server.lua_scripts);
        while((de = dictNext(di)) != NULL) {
            robj *body = dictGetVal(de);
            if (rdbSaveAuxField(rdb,"lua",3,body->ptr,sdslen(body->ptr)) == -1)
                goto werr;
        }
        dictReleaseIterator(di);
        di = NULL; /* So that we don't release it again on error. */
    }

    if (rdbSaveModulesAux(rdb, REDISMODULE_AUX_AFTER_RDB) == -1) goto werr;

    /* EOF opcode */
    if (rdbSaveType(rdb,RDB_OPCODE_EOF) == -1) goto werr;

    /* CRC64 checksum. It will be zero if checksum computation is disabled, the
     * loading code skips the check in this case. */
    cksum = rdb->cksum;
    memrev64ifbe(&cksum);
    if (rioWrite(rdb,&cksum,8) == 0) goto werr;
    return C_OK;

werr:
    if (error) *error = errno;
    if (di) dictReleaseIterator(di);
    return C_ERR;
}