Redis VM and RedisVM

Redis VM and RedisVM

This article is original freas_1990, reprint please indicate the source: http://blog.csdn.net/freas_1990/article/details/42052813

When the value of a key of Redis is swap to a file, the RedisObject to which the value of the key points will be changed to VMPointer, which stores the information of the value on the disk file, including the offset of the start page and the number of consecutive pages.

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;

The logic for importing the value of this key into the memory is as follows:

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;}

By now, the essence of redis VM has been broken. Do you understand?