How to expose and monitor cache hit/miss rates with expvar in Go?

To expose and monitor cache hit/miss rates with expvar in Go, you can follow these steps:

Step 1: Create a struct to represent your cache and store hit/miss counts. For example:

type Cache struct {
    hits  int
    misses int
    // other cache fields
}

Step 2: Implement methods to get and set values in the cache. Update the hit/miss counts accordingly. For example:

func (c *Cache) Get(key string) (interface{}, bool) {
    // check if key exists
    // if found, increment the hits count
    // otherwise, increment the misses count
    // return the value and a flag indicating if the key was found
}

func (c *Cache) Set(key string, value interface{}) {
    // set the value in the cache
}

Step 3: Define expvar variables to expose the hit/miss counts. For example:

var (
    hitsVar   = expvar.NewInt("cache.hits")
    missesVar = expvar.NewInt("cache.misses")
)

Step 4: Implement the expvar.Var interface for the hit/miss counts. For example:

func (c *Cache) String() string {
    return fmt.Sprintf(`{"hits": %d, "misses": %d}`, c.hits, c.misses)
}

Step 5: Register the hit/miss counts with expvar. For example:

expvar.Publish("cache", expvar.Func(func() interface{} {
    return cache.String()
}))

Step 6: Use the cache in your application, making sure to call the appropriate methods (e.g., Get and Set) and update the hit/miss counts.

Step 7: You can then access the hit/miss counts by running your Go program and visiting the /debug/vars endpoint, or by using the expvar package to extract the values programmatically. For example:

cacheHits := expvar.Get("cache.hits").(*expvar.Int).Value()
cacheMisses := expvar.Get("cache.misses").(*expvar.Int).Value()

By following these steps, you can expose and monitor cache hit/miss rates using expvar in Go.