原创文章是freas_1990。转载请注明出处:http://blog.csdn.net/freas_1990/article/details/42052813
Redis唯一的那个key的value是swap文件上的时候,该key的value指向的RedisObject将会改变成VMPointer。VMPointer保存了该value在磁盘文件上的信息,包含起始页面的偏移和连续的页面数等。
typedef struct redisObject { unsigned type:4; unsigned storage:2; /* REDIS_VM_MEMORY or REDIS_VM_SWAPPING */ unsigned encoding:4; unsigned lru:22; /* lru time (relative to server.lruclock) */ int refcount; void *ptr; /* VM fields are only allocated if VM is active, otherwise the * object allocation function will just allocate * sizeof(redisObjct) minus sizeof(redisObjectVM), so using * Redis without VM active will not have any overhead. */ } robj;
typedef struct vmPointer { unsigned type:4; unsigned storage:2; /* REDIS_VM_SWAPPED or REDIS_VM_LOADING */ unsigned notused:26; unsigned int vtype; /* type of the object stored in the swap file */ off_t page; /* the page at witch the object is stored on disk */ off_t usedpages; /* number of pages used on disk */ } vmpointer;
将该key的value导入内存的逻辑例如以下:
robj *vmReadObjectFromSwap(off_t page, int type) { robj *o; if (server.vm_enabled) pthread_mutex_lock(&server.io_swapfile_mutex); if (fseeko(server.vm_fp,page*server.vm_page_size,SEEK_SET) == -1) { redisLog(REDIS_WARNING, "Unrecoverable VM problem in vmReadObjectFromSwap(): can't seek: %s", strerror(errno)); _exit(1); } o = rdbLoadObject(type,server.vm_fp); if (o == NULL) { redisLog(REDIS_WARNING, "Unrecoverable VM problem in vmReadObjectFromSwap(): can't load object from swap file: %s", strerror(errno)); _exit(1); } if (server.vm_enabled) pthread_mutex_unlock(&server.io_swapfile_mutex); return o; }
到这里,redis VM已经指出的精髓,明白了吧?
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时间: 2024-10-13 19:31:57