Remove validity from FIFO cache

We can remove the validity setting of 1h in 2.4 for the
chunks cache because it doesn't reduce memory usage and instead leads to
valid chunks being ignore when querying the cache. Chunks are immutable
so it doesn't make sense to not return them if they are present in the
cache.

Closes #4922

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

pkg/canary/reader/reader.go

@@ -129,6 +129,7 @@ func NewReader(writer io.Writer,
 			fmt.Fprintf(rd.w, "shutting down reader\n")
 			rd.shuttingDown = true
 			_ = rd.conn.Close()
+			rd.conn = nil
 		}
 	}()
 

pkg/storage/chunk/cache/fifo_cache.go

@@ -69,7 +69,6 @@ type FifoCache struct {
 	maxSizeItems  int
 	maxSizeBytes  uint64
 	currSizeBytes uint64
-	validity      time.Duration
 
 	entries map[string]*list.Element
 	lru     *list.List
@@ -80,7 +79,6 @@ type FifoCache struct {
 	entriesCurrent  prometheus.Gauge
 	totalGets       prometheus.Counter
 	totalMisses     prometheus.Counter
-	staleGets       prometheus.Counter
 	memoryBytes     prometheus.Gauge
 }
 
@@ -109,7 +107,6 @@ func NewFifoCache(name string, cfg FifoCacheConfig, reg prometheus.Registerer, l
 	return &FifoCache{
 		maxSizeItems: cfg.MaxSizeItems,
 		maxSizeBytes: maxSizeBytes,
-		validity:     cfg.Validity,
 		entries:      make(map[string]*list.Element),
 		lru:          list.New(),
 
@@ -161,14 +158,6 @@ func NewFifoCache(name string, cfg FifoCacheConfig, reg prometheus.Registerer, l
 			ConstLabels: prometheus.Labels{"cache": name},
 		}),
 
-		staleGets: promauto.With(reg).NewCounter(prometheus.CounterOpts{
-			Namespace:   "querier",
-			Subsystem:   "cache",
-			Name:        "stale_gets_total",
-			Help:        "The total number of Get calls that had an entry which expired",
-			ConstLabels: prometheus.Labels{"cache": name},
-		}),
-
 		memoryBytes: promauto.With(reg).NewGauge(prometheus.GaugeOpts{
 			Namespace:   "querier",
 			Subsystem:   "cache",
@@ -284,13 +273,7 @@ func (c *FifoCache) Get(ctx context.Context, key string) ([]byte, bool) {
 	element, ok := c.entries[key]
 	if ok {
 		entry := element.Value.(*cacheEntry)
-		if c.validity == 0 || time.Since(entry.updated) < c.validity {
-			return entry.value, true
-		}
-
-		c.totalMisses.Inc()
-		c.staleGets.Inc()
-		return nil, false
+		return entry.value, true
 	}
 
 	c.totalMisses.Inc()