Enable fifo cache by default

pkg/storage/chunk/cache/cache.go

@@ -25,6 +25,7 @@ type Cache interface {
 
 // Config for building Caches.
 type Config struct {
+	autoEnableFifo  bool
 	EnableFifoCache bool `yaml:"enable_fifocache"`
 
 	DefaultValidity time.Duration `yaml:"default_validity"`
@@ -43,15 +44,21 @@ type Config struct {
 }
 
 // RegisterFlagsWithPrefix adds the flags required to config this to the given FlagSet
-func (cfg *Config) RegisterFlagsWithPrefix(prefix string, description string, f *flag.FlagSet) {
+func (cfg *Config) RegisterFlagsWithPrefix(prefix string, description string, f *flag.FlagSet, autoEnableFifo bool) {
+	cfg.autoEnableFifo = autoEnableFifo
 	cfg.Background.RegisterFlagsWithPrefix(prefix, description, f)
 	cfg.Memcache.RegisterFlagsWithPrefix(prefix, description, f)
 	cfg.MemcacheClient.RegisterFlagsWithPrefix(prefix, description, f)
 	cfg.Redis.RegisterFlagsWithPrefix(prefix, description, f)
 	cfg.Fifocache.RegisterFlagsWithPrefix(prefix, description, f)
+	f.DurationVar(&cfg.DefaultValidity, prefix+"default-validity", time.Hour, description+"The default validity of entries for caches unless overridden.")
 
-	f.BoolVar(&cfg.EnableFifoCache, prefix+"cache.enable-fifocache", false, description+"Enable in-memory cache.")
-	f.DurationVar(&cfg.DefaultValidity, prefix+"default-validity", 0, description+"The default validity of entries for caches unless overridden.")
+	enableFifoDescription := "Enable in-memory cache"
+	if cfg.autoEnableFifo {
+		enableFifoDescription += " (auto-enabled if no other cache is configured)"
+	}
+	enableFifoDescription += "."
+	f.BoolVar(&cfg.EnableFifoCache, prefix+"cache.enable-fifocache", false, description+enableFifoDescription)
 
 	cfg.Prefix = prefix
 }
@@ -68,16 +75,6 @@ func New(cfg Config, reg prometheus.Registerer, logger log.Logger) (Cache, error
 
 	caches := []Cache{}
 
-	if cfg.EnableFifoCache {
-		if cfg.Fifocache.Validity == 0 && cfg.DefaultValidity != 0 {
-			cfg.Fifocache.Validity = cfg.DefaultValidity
-		}
-
-		if cache := NewFifoCache(cfg.Prefix+"fifocache", cfg.Fifocache, reg, logger); cache != nil {
-			caches = append(caches, Instrument(cfg.Prefix+"fifocache", cache, reg))
-		}
-	}
-
 	if (cfg.MemcacheClient.Host != "" || cfg.MemcacheClient.Addresses != "") && cfg.Redis.Endpoint != "" {
 		return nil, errors.New("use of multiple cache storage systems is not supported")
 	}
@@ -103,6 +100,16 @@ func New(cfg Config, reg prometheus.Registerer, logger log.Logger) (Cache, error
 		caches = append(caches, NewBackground(cacheName, cfg.Background, Instrument(cacheName, cache, reg), reg))
 	}
 
+	if cfg.EnableFifoCache || (cfg.autoEnableFifo && len(caches) == 0) {
+		if cfg.Fifocache.Validity == 0 && cfg.DefaultValidity != 0 {
+			cfg.Fifocache.Validity = cfg.DefaultValidity
+		}
+
+		if cache := NewFifoCache(cfg.Prefix+"fifocache", cfg.Fifocache, reg, logger); cache != nil {
+			caches = append(caches, Instrument(cfg.Prefix+"fifocache", cache, reg))
+		}
+	}
+
 	cache := NewTiered(caches)
 	if len(caches) > 1 {
 		cache = Instrument(cfg.Prefix+"tiered", cache, reg)

pkg/storage/chunk/cache/fifo_cache.go

@@ -39,7 +39,7 @@ type FifoCacheConfig struct {
 
 // RegisterFlagsWithPrefix adds the flags required to config this to the given FlagSet
 func (cfg *FifoCacheConfig) RegisterFlagsWithPrefix(prefix, description string, f *flag.FlagSet) {
-	f.StringVar(&cfg.MaxSizeBytes, prefix+"fifocache.max-size-bytes", "", description+"Maximum memory size of the cache in bytes. A unit suffix (KB, MB, GB) may be applied.")
+	f.StringVar(&cfg.MaxSizeBytes, prefix+"fifocache.max-size-bytes", "1GB", description+"Maximum memory size of the cache in bytes. A unit suffix (KB, MB, GB) may be applied.")
 	f.IntVar(&cfg.MaxSizeItems, prefix+"fifocache.max-size-items", 0, description+"Maximum number of entries in the cache.")
 	f.DurationVar(&cfg.Validity, prefix+"fifocache.duration", 0, description+"The expiry duration for the cache.")
 

pkg/storage/chunk/chunk_store.go

@@ -70,9 +70,9 @@ type StoreConfig struct {
 
 // RegisterFlags adds the flags required to config this to the given FlagSet
 func (cfg *StoreConfig) RegisterFlags(f *flag.FlagSet) {
-	cfg.ChunkCacheConfig.RegisterFlagsWithPrefix("store.chunks-cache.", "Cache config for chunks. ", f)
+	cfg.ChunkCacheConfig.RegisterFlagsWithPrefix("store.chunks-cache.", "Cache config for chunks. ", f, true)
 	f.BoolVar(&cfg.chunkCacheStubs, "store.chunks-cache.cache-stubs", false, "If true, don't write the full chunk to cache, just a stub entry.")
-	cfg.WriteDedupeCacheConfig.RegisterFlagsWithPrefix("store.index-cache-write.", "Cache config for index entry writing. ", f)
+	cfg.WriteDedupeCacheConfig.RegisterFlagsWithPrefix("store.index-cache-write.", "Cache config for index entry writing. ", f, false)
 
 	f.Var(&cfg.CacheLookupsOlderThan, "store.cache-lookups-older-than", "Cache index entries older than this period. 0 to disable.")
 }

pkg/storage/chunk/storage/factory.go

@@ -114,7 +114,7 @@ func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
 	cfg.GrpcConfig.RegisterFlags(f)
 
 	f.StringVar(&cfg.Engine, "store.engine", "chunks", "The storage engine to use: chunks or blocks.")
-	cfg.IndexQueriesCacheConfig.RegisterFlagsWithPrefix("store.index-cache-read.", "Cache config for index entry reading. ", f)
+	cfg.IndexQueriesCacheConfig.RegisterFlagsWithPrefix("store.index-cache-read.", "Cache config for index entry reading. ", f, false)
 	f.DurationVar(&cfg.IndexCacheValidity, "store.index-cache-validity", 5*time.Minute, "Cache validity for active index entries. Should be no higher than -ingester.max-chunk-idle.")
 	f.BoolVar(&cfg.DisableBroadIndexQueries, "store.disable-broad-index-queries", false, "Disable broad index queries which results in reduced cache usage and faster query performance at the expense of somewhat higher QPS on the index store.")
 }