Function dbRandomKey

src/db.cpp:429–468

Return a random key, in form of a Redis object. * If there are no keys, NULL is returned. * * The function makes sure to return keys not already expired. */

 *
 * The function makes sure to return keys not already expired. */
robj *dbRandomKey(redisDb *db) {
    int maxtries = 100;
    bool allvolatile = db->expireSize() == db->size();

    while(1) {
        sds key;
        robj *keyobj;

        auto itr = db->random();
        if (itr == nullptr) return NULL;

        key = itr.key();
        keyobj = createStringObject(key,sdslen(key));

        if (itr.val()->FExpires())
        {
            if (allvolatile && listLength(g_pserver->masters) && --maxtries == 0) {
                /* If the DB is composed only of keys with an expire set,
                    * it could happen that all the keys are already logically
                    * expired in the replica, so the function cannot stop because
                    * expireIfNeeded() is false, nor it can stop because
                    * dictGetRandomKey() returns NULL (there are keys to return).
                    * To prevent the infinite loop we do some tries, but if there
                    * are the conditions for an infinite loop, eventually we
                    * return a key name that may be already expired. */
                return keyobj;
            }
        }
            
        if (itr.val()->FExpires())
        {
             if (expireIfNeeded(db,keyobj)) {
                decrRefCount(keyobj);
                continue; /* search for another key. This expired. */
             }
        }
        
        return keyobj;
    }
}

bool redisDbPersistentData::syncDelete(robj *key)
{