Lay Bare Redis VMS

The original article is freas_1990. Reprint Please specify source: http://blog.csdn.net/freas_1990/article/details/42052813

The value of the only key that Redis has is the swap file, and the key's value points to the redisobject that will change to Vmpointer. Vmpointer holds the value's information on the disk file, including the offset of the starting 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 was only allocated if VM is active, otherwise the     * Object allocation function would just allocate     * sizeof (REDISOBJCT) minus sizeof (REDISOBJECTVM), so using     * Redis without VM active is not having any overhead. */} RO bj

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 was stored on disk */    off_t usedpages;    /* Number of pages used on disk */} Vmpointer;

The logic for importing the key's value into 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;}

Here, the Redis VM has pointed out the essence, understand it?

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Lay bare redis VMS