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点破Redis的VM
Redis的某一个key的value被swap到文件上的时候,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,包括起始页面的偏移和连续的页面数等。
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- 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;
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- 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导入内存的逻辑如下:
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- 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;
- }
点破Redis的VM
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