/* Redis database representation. There are multiple databases identified * by integers from 0 (the default database) up to the max configured * database. The database number is the 'id' field in the structure. */typedef struct redisDb { dict *dict;     /* The keyspace for this DB */ dict *expires;    /* 過期字典*/ dict *blocking_keys;  /* Keys with clients waiting for data (BLPOP) */ dict *ready_keys;   /* Blocked keys that received a PUSH */ dict *watched_keys;   /* WATCHED keys for MULTI/EXEC CAS */ struct evictionPoolEntry *eviction_pool; /* Eviction pool of keys */ int id;      /* Database ID */ long long avg_ttl;   /* Average TTL, just for stats */} redisDb;

void setExpire(redisDb *db, robj *key, long long when) { dictEntry *kde, *de; /* Reuse the sds from the main dict in the expire dict */ kde = dictFind(db->dict,key->ptr); redisAssertWithInfo(NULL,key,kde != NULL); de = dictReplaceRaw(db->expires,dictGetKey(kde)); dictSetSignedIntegerVal(de,when);}

robj *lookupKeyRead(redisDb *db, robj *key) { robj *val; expireIfNeeded(db,key); // 切入點(diǎn) val = lookupKey(db,key); if (val == NULL)  server.stat_keyspace_misses++; else  server.stat_keyspace_hits++; return val;}

for (j = 0; j < dbs_per_call; j++) { int expired; redisDb *db = server.db+(current_db % server.dbnum); /* Increment the DB now so we are sure if we run out of time  * in the current DB we'll restart from the next. This allows to  * distribute the time evenly across DBs. */ current_db++; /* Continue to expire if at the end of the cycle more than 25%  * of the keys were expired. */ do {  unsigned long num, slots;  long long now, ttl_sum;  int ttl_samples;  /* 如果該db沒有設(shè)置過期key，則繼續(xù)看下個(gè)db*/  if ((num = dictSize(db->expires)) == 0) {   db->avg_ttl = 0;   break;  }  slots = dictSlots(db->expires);  now = mstime();  /* When there are less than 1% filled slots getting random   * keys is expensive, so stop here waiting for better times...   * The dictionary will be resized asap. */  if (num && slots > DICT_HT_INITIAL_SIZE &&   (num*100/slots < 1)) break;  /* The main collection cycle. Sample random keys among keys   * with an expire set, checking for expired ones. */  expired = 0;  ttl_sum = 0;  ttl_samples = 0;  if (num > ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP)   num = ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP;// 20  while (num--) {   dictEntry *de;   long long ttl;   if ((de = dictGetRandomKey(db->expires)) == NULL) break;   ttl = dictGetSignedIntegerVal(de)-now;   if (activeExpireCycleTryExpire(db,de,now)) expired++;   if (ttl > 0) {    /* We want the average TTL of keys yet not expired. */    ttl_sum += ttl;    ttl_samples++;   }  }  /* Update the average TTL stats for this database. */  if (ttl_samples) {   long long avg_ttl = ttl_sum/ttl_samples;   /* Do a simple running average with a few samples.    * We just use the current estimate with a weight of 2%    * and the previous estimate with a weight of 98%. */   if (db->avg_ttl == 0) db->avg_ttl = avg_ttl;   db->avg_ttl = (db->avg_ttl/50)*49 + (avg_ttl/50);  }  /* We can't block forever here even if there are many keys to   * expire. So after a given amount of milliseconds return to the   * caller waiting for the other active expire cycle. */  iteration++;  if ((iteration & 0xf) == 0) { /* 每迭代16次檢查一次 */   long long elapsed = ustime()-start;   latencyAddSampleIfNeeded("expire-cycle",elapsed/1000);   if (elapsed > timelimit) timelimit_exit = 1;  } // 超過時(shí)間限制則退出  if (timelimit_exit) return;  /* 在當(dāng)前db中，如果少于25%的key過期，則停止繼續(xù)刪除過期key */ } while (expired > ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP/4);}