FIFO cache to support eviction based on memory usage

CHANGELOG.md

@@ -92,9 +92,9 @@
 * [ENHANCEMENT] Output all config fields to /config API, including those with empty value. #2209
 * [ENHANCEMENT] Add "missing_metric_name" and "metric_name_invalid" reasons to cortex_discarded_samples_total metric. #2346
 * [ENHANCEMENT] Experimental TSDB: sample ingestion errors are now reported via existing `cortex_discarded_samples_total` metric. #2370
+* [ENHANCEMENT] FIFO cache to support eviction based on memory usage. The `-<prefix>.fifocache.size` CLI flag has been renamed to `-<prefix>.fifocache.max-size-items` as well as its YAML config option `size` renamed to `max_size_items`. Added `-<prefix>.fifocache.max-size-bytes` CLI flag and YAML config option `max_size_bytes` to specify memory limit of the cache. #2319
 * [BUGFIX] Ensure user state metrics are updated if a transfer fails. #2338
 * [BUGFIX] Fixed etcd client keepalive settings. #2278
-* [BUGFIX] Fixed bug in updating last element of FIFO cache. #2270
 * [BUGFIX] Register the metrics of the WAL. #2295
 
 ### config file breaking changes

docs/configuration/config-file-reference.md

@@ -2271,13 +2271,22 @@ The `fifo_cache_config` configures the local in-memory cache. The supported CLI
  
 
 ```yaml
-# The number of entries to cache.
-# CLI flag: -<prefix>.fifocache.size
-[size: <int> | default = 0]
+# Maximum memory size of the cache.
+# CLI flag: -<prefix>.fifocache.max-size-bytes
+[max_size_bytes: <int> | default = 0]
+
+# Maximum number of entries in the cache.
+# CLI flag: -<prefix>.fifocache.max-size-items
+[max_size_items: <int> | default = 0]
 
 # The expiry duration for the cache.
 # CLI flag: -<prefix>.fifocache.duration
 [validity: <duration> | default = 0s]
+
+# Deprecated (use max-size-items or max-size-bytes instead): The number of
+# entries to cache.
+# CLI flag: -<prefix>.fifocache.size
+[size: <int> | default = 0]
 ```
 
 ### `configs_config`

docs/production/caching.md

@@ -81,8 +81,10 @@ To enable the FIFO cache, use the following flags:
     Enable in-memory cache.
 -<prefix>.fifocache.duration duration
     The expiry duration for the cache.
--<prefix>.fifocache.size int
-    The number of entries to cache.
+-<prefix>.fifocache.max-size-bytes int
+    Maximum memory size of the cache.
+-<prefix>.fifocache.max-size-items int
+    Maximum number of entries in the cache.
 ```
 
 See [`fifo_cache_config` documentation](../configuration/config-file-reference.md#fifo-cache-config) if you use a config file with Cortex.

pkg/chunk/cache/cache.go

@@ -68,8 +68,9 @@ func New(cfg Config) (Cache, error) {
 			cfg.Fifocache.Validity = cfg.DefaultValidity
 		}
 
-		cache := NewFifoCache(cfg.Prefix+"fifocache", cfg.Fifocache)
-		caches = append(caches, Instrument(cfg.Prefix+"fifocache", cache))
+		if cache := NewFifoCache(cfg.Prefix+"fifocache", cfg.Fifocache); cache != nil {
+			caches = append(caches, Instrument(cfg.Prefix+"fifocache", cache))
+		}
 	}
 
 	if (cfg.MemcacheClient.Host != "" || cfg.MemcacheClient.Addresses != "") && cfg.Redis.Endpoint != "" {

pkg/chunk/cache/cache_test.go

@@ -172,7 +172,7 @@ func TestMemcache(t *testing.T) {
 }
 
 func TestFifoCache(t *testing.T) {
-	cache := cache.NewFifoCache("test", cache.FifoCacheConfig{Size: 1e3, Validity: 1 * time.Hour})
+	cache := cache.NewFifoCache("test", cache.FifoCacheConfig{MaxSizeItems: 1e3, Validity: 1 * time.Hour})
 	testCache(t, cache)
 }