create a key succeed by INCR command,but it's LFU is not initial value 5.

[FNST-zhoush]

127.0.0.1:4001> incr key
(integer) 1
127.0.0.1:4001> object freq key
(integer) 0
127.0.0.1:4001> incr key
(integer) 2
127.0.0.1:4001> object freq key
(integer) 1
127.0.0.1:4001> set key2 1
OK
127.0.0.1:4001> object freq key2
(integer) 5

[youjiali1995]

Redis creates shared objects including integer 0-9999.

[soloestoy]

Redis creates shared objects including integer 0-9999.

Yes, and if you wanna use accurate LFU, please config set maxmemory-policy *-lfu.

[FNST-zhoush]

i have already configed maxmemory-policy allkes-lfu and maxmemory 1G.

127.0.0.1:4001> config get maxmemory-policy

1. "maxmemory-policy"
2. "allkeys-lfu"
   127.0.0.1:4001> config get maxmemory
3. "maxmemory"
4. "1000000000"
   127.0.0.1:4001> flushall
   OK
   127.0.0.1:4001> incr key
   (integer) 1
   127.0.0.1:4001> object freq key
   (integer) 0
   127.0.0.1:4001> incr key
   (integer) 2
   127.0.0.1:4001> object freq key
   (integer) 1
   127.0.0.1:4001> set key2 1
   OK
   127.0.0.1:4001> object freq key2
   (integer) 5

In my point, there is not LFU(on/off) check in createStringObjectFromLongLong.

[ccqy66]

@FNST-zhoush

Redis creates shared objects including integer 0-9999.

so we can see redis how to create the shared integer objects from redis-4.0.2

void createSharedObjects(void) {
...
 for (j = 0; j < OBJ_SHARED_INTEGERS; j++) {
        shared.integers[j] =
            makeObjectShared(createObject(OBJ_STRING,(void*)(long)j));
        shared.integers[j]->encoding = OBJ_ENCODING_INT;
  }
...
}
robj *createObject(int type, void *ptr) {
    ...
    if (server.maxmemory_policy & MAXMEMORY_FLAG_LFU) {
        o->lru = (LFUGetTimeInMinutes()<<8) | LFU_INIT_VAL;
    } else {
        o->lru = LRU_CLOCK();
    }
    return o;
}

so,I think if you set maxmemory_policy=allkeys-lfu,lfu counter should be LFU_INIT_VAL.something else,you can provide some extra infomation.for example redis version. or read source code

[FNST-zhoush]

void incrDecrCommand(client *c, long long incr) {
	...
    if (o && o->refcount == 1 && o->encoding == OBJ_ENCODING_INT &&
        (value < 0 || value >= OBJ_SHARED_INTEGERS) &&
        value >= LONG_MIN && value <= LONG_MAX)
    {
        new = o;
        o->ptr = (void*)((long)value);
    } else {
        new = createStringObjectFromLongLong(value);
        if (o) {
            dbOverwrite(c->db,c->argv[1],new);
        } else {
            dbAdd(c->db,c->argv[1],new);
        }
    }
}

robj *createStringObjectFromLongLong(long long value) {
    robj *o;
    if (value >= 0 && value < OBJ_SHARED_INTEGERS) {
        incrRefCount(shared.integers[value]);
        o = shared.integers[value];
	}else 
	    ...
}

if o doesn't exist,INCR command can create a key by createStringObjectFromLongLong.
but it is a shard object evenif maxmemory-policy configured allkes-lfu and maxmemory=1G.
i think we should avoid using shared integers when maxmemory & maxmemory-policy is used because every object needs to have a private LFU field for the LFU algorithm to work well.

[shenlongxing]

It is a bug, and i open a PR to fix this problem.#5011

[ccqy66]

@shenlongxing I think the purpose of algorithm of evicting is eliminating extra memory, the pr will create more object,and run algorithm to evict it.so I think it's waste of memory,if it's share object,it should exist all the time.

[shenlongxing]

@ccqy66 I do not agree.
The key point is the newly created object can not be a shared one once maxmemory-policy is set to *-lfu.

[FNST-zhoush]

@antirez It's a bug in my point. What do you think?