Request Get Expiration With Get

[MrSametBurgazoglu]

Clarification and motivation

I have a script that updating some variables and users get them from cache. But I want to get expiration for showing them last update time.

Acceptance criteria

Get expiration time with get function or new function with expiration time

[maypok86]

Hi, thanks for the issue.

I was going to rework the API a bit later. For now you can use something like this.

package main

import (
	"time"

	"github.com/maypok86/otter"
)

type WithTime[V any] struct {
	Value     V
	UpdatedAt time.Time // or in seconds
}

type Cache[K comparable, V any] struct {
	cache otter.Cache[K, WithTime[V]]
}

func NewCache[K comparable, V any](capacity int) (*Cache[K, V], error) {
	b, err := otter.NewBuilder[K, WithTime[V]](capacity)
	if err != nil {
		return nil, err
	}

	c, err := b.WithTTL(time.Hour).Build()
	if err != nil {
		return nil, err
	}

	return &Cache[K, V]{
		cache: c,
	}, nil
}

func (c *Cache[K, V]) Get(key K) (WithTime[V], bool) {
	return c.cache.Get(key)
}

func (c *Cache[K, V]) Set(key K, value V) bool {
	updatedAt := time.Now()
	return c.cache.Set(key, WithTime[V]{
		Value:     value,
		UpdatedAt: updatedAt,
	})
}

[maypok86]

@MrSametBurgazoglu @proost

What do you think of this solution to this problem? It's a bit non-standard for Go, but allows otter to hide a lot of future features.

c, err := MustBuilder[int, int](256).
	WithTTL(time.Hour).
	Build()

...

// if you want to get the value without updating the eviction policy
value, ok := c.Advanced().GetQuietly(1)

...

// if you want to get an entry
entry, ok := c.Advanced().GetEntry(1)

...

// if you want to get an entry without updating the eviction policy
entry, ok := c.Advanced().GetEntryQuietly(1)

...

key := entry.Key()
value := entry.Value()
cost := entry.Cost()
expiration := entry.Expiration()
ttl := entry.TTL()
hasExpired := entry.HasExpired()

[proost]

@maypok86
First, I want this feature because i plan to apply PER

your proposed API can hide underneath a lot of features. what do you expect to user if user get cost, ttl?

GetEntryQuietly is good to mitigate cache miss storm. what is meaning of parameter?

And I think Advanced() is not intuitive name for accessing additional cache functionality. how about Details() or WithMetadata()?

[maypok86]

your proposed API can hide underneath a lot of features. what do you expect to user if user get cost, ttl?

I assumed something like this

key := 1

...

func (c *Cache[K, V]) GetCost(key K) (uint32, error) {
    entry, ok := c.Advanced().GetEntryQuietly(key)
    if !ok {
        return 0, errors.New("a cache entry was not found")
    }
    return entry.Cost(), nil
}

what is meaning of parameter?

In all cases, 1 is just a key.

Advanced() is not intuitive name for accessing additional cache functionality.

This is a difficult moment. It is unclear which name is better to give. I was also thinking about something like Features or Details, but I'm very likely to add more than just functions to get values there, and then Details will become strange.

[proost]

This is a difficult moment. It is unclear which name is better to give. I was also thinking about something like Features or Details, but I'm very likely to add more than just functions to get values there, and then Details will become strange.

how about Extended()? Advanced() is unfamiliar name.

your proposed API can hide underneath a lot of features. what do you expect to user if user get cost, ttl?

I mean what is use case if user can get cost or ttl?

[maypok86]

how about Extended()?

Hmm, it looks interesting. But probably just Extension will be clearer.

[maypok86]

@proost So, I think we've come to an agreement, right?

[MrSametBurgazoglu]

@maypok86 I apologize for not being able to answer. Speaking for myself, this is a good solution. But I didn't understand the meaning of updating eviction policy.

[maypok86]

@MrSametBurgazoglu During a Get operation, caches usually additionally update the eviction policy to better predict eviction when the maximum size is reached based on recency (lru) and frequency (lfu). And more effective eviction policies use both of these metrics. But sometimes there are situations when you need to complete several requests that are not related to the main workload and you do not want them to damage the eviction policy. That is, if you want the cache on these requests to work simply as a hash table, you can use the GetQuietly or GetEntryQuietly methods.

[proost]

@maypok86 I agree. Thank you for a new feature!