redis lru实现策略

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1. server.lruclock = getLRUClock();
   
2. getLRUClock函数如下:
   
3. #define LRU_CLOCK_RESOLUTION 1000 /* LRU clock resolution in ms */
   
4. #define LRU_BITS 24
   
5. #define LRU_CLOCK_MAX ((1<lru */
   
6. /* Return the LRU clock, based on the clock resolution. This is a time
   
7.  * in a reduced-bits format that can be used to set and check the
   
8.  * object->lru field of redisObject structures. */
   
9. 
   
10.   unsigned int getLRUClock(void) {
    
11.         return (mstime()/LRU_CLOCK_RESOLUTION) & LRU_CLOCK_MAX;
    
12.   }

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1. typedef struct redisObject {
   
2.      unsigned type:4;
   
3.      unsigned encoding:4;
   
4.      unsigned lru:LRU_BITS; /* LRU time (relative to server.lruclock) or
   
5.                              * LFU data (least significant 8 bits frequency
   
6.                              * and most significant 16 bits decreas time). */
   
7.      int refcount;
   
8.      void *ptr;
   
9.      } robj

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1. /* Low level key lookup API, not actually called directly from commands
   
2. * implementations that should instead rely on lookupKeyRead(),
   
3. * lookupKeyWrite() and lookupKeyReadWithFlags(). */
   
4.   robj *lookupKey(redisDb *db, robj *key, int flags) {
   
5.   dictEntry *de = dictFind(db->dict,key->ptr);
   
6.   if (de) {
   
7.      robj *val = dictGetVal(de);
   
8. 
   
9. /* Update the access time for the ageing algorithm.
   
10. * Don't do it if we have a saving child, as this will trigger
    
11. * a copy on write madness. */
    
12. if (server.rdb_child_pid == -1 &&
    
13.     server.aof_child_pid == -1 &&
    
14.     !(flags & LOOKUP_NOTOUCH))
    
15.    {
    
16.    if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
    
17.    unsigned long ldt = val->lru >> 8;
    
18.    unsigned long counter = LFULogIncr(val->lru & 255);
    
19.    val->lru = (ldt << 8) | counter;
    
20.    } else {
    
21.    val->lru = LRU_CLOCK();
    
22.   }
    
23.   }
    
24.    return val;
    
25.   } else {
    
26.   return NULL;
    
27.  }
    
28.  }

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