[BUG]: cost added always differ by 56

[toshinari123]

What version of Ristretto are you using?

the latest

What version of Go are you using?

go version go1.21.5 linux/amd64

Have you tried reproducing the issue with the latest release?

Yes

What is the hardware spec (RAM, CPU, OS)?

linux mint victoria xfce

CPU:
Info: quad core model: Intel Core i5-8265U bits: 64 type: MT MCP
smt: enabled arch: Comet/Whiskey Lake note: check rev: C cache: L1: 256 KiB
L2: 1024 KiB L3: 6 MiB
Speed (MHz): avg: 800 min/max: 400/3900 cores: 1: 800 2: 800 3: 800
4: 800 5: 800 6: 800 7: 800 8: 800 bogomips: 28800
Flags: avx avx2 ht lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx

RAM:
2 times the following
Total Width: 64 bits
Data Width: 64 bits
Size: 8 GB
Form Factor: SODIMM
Set: None
Locator: ChannelA-DIMM0
Bank Locator: BANK 0
Type: DDR4
Type Detail: Synchronous
Speed: 2667 MT/s
Manufacturer: Samsung
Serial Number: 00000000
Asset Tag: None
Part Number: M471A1K43BB1-CTD
Rank: 1
Configured Memory Speed: 2400 MT/s

What steps will reproduce the bug?

run go test with following test_test.go code:

package ristretto_test

import (
	"bytes"
	"time"
	"testing"

	"github.com/dgraph-io/ristretto"
	"github.com/stretchr/testify/assert"
)

func TestGetContent(t *testing.T) {
	cache, _ := ristretto.NewCache(&ristretto.Config{
		NumCounters: 1e7,
		MaxCost:     128,
		BufferItems: 64,
		Metrics:     true,
	})

	added := cache.Set("id1", bytes.NewBuffer([]byte("a")), 1)
	time.Sleep(100 * time.Millisecond) //https://github.com/dgraph-io/ristretto/issues/161
	assert.Equal(t, true, added)
	assert.Equal(t, uint64(1), cache.Metrics.CostAdded())

	added = cache.Set("id1", bytes.NewBuffer([]byte("b")), 2)
	time.Sleep(100 * time.Millisecond) 
	assert.Equal(t, true, added)
	assert.Equal(t, uint64(2), cache.Metrics.CostAdded())

	added = cache.Set("id1", bytes.NewBuffer([]byte("c")), 100)
	time.Sleep(100 * time.Millisecond) 
	assert.Equal(t, true, added)
	assert.Equal(t, uint64(100), cache.Metrics.CostAdded())	//will be 0x9c which is 156

	added = cache.Set("id2", bytes.NewBuffer([]byte("b")), 10)
	time.Sleep(100 * time.Millisecond) 
	assert.Equal(t, true, added)
	assert.Equal(t, uint64(110), cache.Metrics.CostAdded()) //will be 0xde which is 222 = 110 + 56 + 56
}

Expected behavior and actual result.

expected behaviour: cost added matches the cost i put in the Set calls

actual result: somehow added by 56 everytime

Additional information

please point me to correct resource if i missed anything on this

[darkn3rd]

This is interesting, anyone know where the extra 56 comes from.

[matthewmcneely]

If you add:

IgnoreInternalCost: true,

to your ristretto.Config, I think your test will pass. This is an indication that you are controlling cost calculation upon .Set. Not sure why internal cost for entries is 56.