Adding experimental flag for Metrics Labels String Interning (#6057)

* Metrics Labels String Interning

Signed-off-by: alanprot <[email protected]>

* Changelog

Signed-off-by: alanprot <[email protected]>

* v1 guarantees

Signed-off-by: alanprot <[email protected]>

---------

Signed-off-by: alanprot <[email protected]>

Author: alanprot

CHANGELOG.md

@@ -17,6 +17,7 @@
 * [ENHANCEMENT] Store Gateway: Log gRPC requests together with headers configured in `http_request_headers_to_log`. #5958
 * [ENHANCEMENT] Upgrade Alpine to 3.19. #6014
 * [ENHANCEMENT] Upgrade go to 1.21.11 #6014
+* [ENHANCEMENT] Ingester: Add a new experimental `-ingester.labels-string-interning-enabled` flag to enable string interning for metrics labels. #6057
 * [BUGFIX] Configsdb: Fix endline issue in db password. #5920
 * [BUGFIX] Ingester: Fix `user` and `type` labels for the `cortex_ingester_tsdb_head_samples_appended_total` TSDB metric. #5952
 * [BUGFIX] Querier: Enforce max query length check for `/api/v1/series` API even though `ignoreMaxQueryLength` is set to true. #6018

docs/configuration/config-file-reference.md

@@ -2971,6 +2971,10 @@ instance_limits:
 # Customize the message contained in limit errors
 # CLI flag: -ingester.admin-limit-message
 [admin_limit_message: <string> | default = "please contact administrator to raise it"]
+
+# Experimental: Enable string interning for metrics labels.
+# CLI flag: -ingester.labels-string-interning-enabled
+[labels_string_interning_enabled: <boolean> | default = false]
 ```
 
 ### `ingester_client_config`

docs/configuration/v1-guarantees.md

@@ -113,3 +113,5 @@ Currently experimental features are:
   - `-ruler.ring.tokens-file-path` (path) CLI flag
 - Native Histograms
   - Ingestion can be enabled by setting `-blocks-storage.tsdb.enable-native-histograms=true` on Ingester.
+- String interning for metrics labels
+  - Enable string interning for metrics labels by setting `-ingester.labels-string-interning-enabled` on Ingester.

pkg/ingester/ingester.go

@@ -134,6 +134,8 @@ type Config struct {
 
 	// For admin contact details
 	AdminLimitMessage string `yaml:"admin_limit_message"`
+
+	LabelsStringInterningEnabled bool `yaml:"labels_string_interning_enabled"`
 }
 
 // RegisterFlags adds the flags required to config this to the given FlagSet
@@ -158,13 +160,18 @@ func (cfg *Config) RegisterFlags(f *flag.FlagSet) {
 
 	f.StringVar(&cfg.AdminLimitMessage, "ingester.admin-limit-message", "please contact administrator to raise it", "Customize the message contained in limit errors")
 
+	f.BoolVar(&cfg.LabelsStringInterningEnabled, "ingester.labels-string-interning-enabled", false, "Experimental: Enable string interning for metrics labels.")
 }
 
 func (cfg *Config) Validate() error {
 	if err := cfg.LifecyclerConfig.Validate(); err != nil {
 		return err
 	}
 
+	if cfg.LabelsStringInterningEnabled {
+		logutil.WarnExperimentalUse("String interning for metrics labels Enabled")
+	}
+
 	return nil
 }
 
@@ -296,6 +303,10 @@ type userTSDB struct {
 	// Cached shipped blocks.
 	shippedBlocksMtx sync.Mutex
 	shippedBlocks    map[ulid.ULID]struct{}
+
+	// Used to dedup strings and keep a single reference in memory
+	labelsStringInterningEnabled bool
+	interner                     util.Interner
 }
 
 // Explicitly wrapping the tsdb.DB functions that we use.
@@ -425,6 +436,9 @@ func (u *userTSDB) PostCreation(metric labels.Labels) {
 	}
 	u.seriesInMetric.increaseSeriesForMetric(metricName)
 	u.labelSetCounter.increaseSeriesLabelSet(u, metric)
+	if u.labelsStringInterningEnabled {
+		metric.InternStrings(u.interner.Intern)
+	}
 }
 
 // PostDeletion implements SeriesLifecycleCallback interface.
@@ -439,6 +453,9 @@ func (u *userTSDB) PostDeletion(metrics map[chunks.HeadSeriesRef]labels.Labels)
 		}
 		u.seriesInMetric.decreaseSeriesForMetric(metricName)
 		u.labelSetCounter.decreaseSeriesLabelSet(u, metric)
+		if u.labelsStringInterningEnabled {
+			metric.ReleaseStrings(u.interner.Release)
+		}
 	}
 }
 
@@ -2047,8 +2064,10 @@ func (i *Ingester) createTSDB(userID string) (*userTSDB, error) {
 		ingestedAPISamples:  util_math.NewEWMARate(0.2, i.cfg.RateUpdatePeriod),
 		ingestedRuleSamples: util_math.NewEWMARate(0.2, i.cfg.RateUpdatePeriod),
 
-		instanceLimitsFn:    i.getInstanceLimits,
-		instanceSeriesCount: &i.TSDBState.seriesCount,
+		instanceLimitsFn:             i.getInstanceLimits,
+		instanceSeriesCount:          &i.TSDBState.seriesCount,
+		interner:                     util.NewInterner(),
+		labelsStringInterningEnabled: i.cfg.LabelsStringInterningEnabled,
 	}
 
 	enableExemplars := false

pkg/ingester/lifecycle_test.go

@@ -42,6 +42,7 @@ func defaultIngesterTestConfig(t testing.TB) Config {
 	cfg.LifecyclerConfig.ID = "localhost"
 	cfg.LifecyclerConfig.FinalSleep = 0
 	cfg.ActiveSeriesMetricsEnabled = true
+	cfg.LabelsStringInterningEnabled = true
 	return cfg
 }
 

pkg/util/strings.go

@@ -6,6 +6,7 @@ import (
 	"unsafe"
 
 	"github.com/bboreham/go-loser"
+	"go.uber.org/atomic"
 )
 
 // StringsContain returns true if the search value is within the list of input values.
@@ -139,3 +140,80 @@ func MergeSortedSlices(ctx context.Context, a ...[]string) ([]string, error) {
 	}
 	return r, nil
 }
+
+type Interner interface {
+	Intern(s string) string
+	Release(s string)
+}
+
+// NewInterner returns a new Interner to be used to intern strings.
+// Based on https://github.com/prometheus/prometheus/blob/726ed124e4468d0274ba89b0934a6cc8c975532d/storage/remote/intern.go#L51
+func NewInterner() Interner {
+	return &pool{
+		pool: map[string]*entry{},
+	}
+}
+
+type pool struct {
+	mtx  sync.RWMutex
+	pool map[string]*entry
+}
+
+type entry struct {
+	refs atomic.Int64
+
+	s string
+}
+
+func newEntry(s string) *entry {
+	return &entry{s: s}
+}
+
+// Intern returns the interned string. It returns the canonical representation of string.
+func (p *pool) Intern(s string) string {
+	if s == "" {
+		return ""
+	}
+
+	p.mtx.RLock()
+	interned, ok := p.pool[s]
+	p.mtx.RUnlock()
+	if ok {
+		interned.refs.Inc()
+		return interned.s
+	}
+	p.mtx.Lock()
+	defer p.mtx.Unlock()
+	if interned, ok := p.pool[s]; ok {
+		interned.refs.Inc()
+		return interned.s
+	}
+
+	p.pool[s] = newEntry(s)
+	p.pool[s].refs.Store(1)
+	return s
+}
+
+// Release releases a reference of the string `s`.
+// If the reference count become 0, the string `s` is removed from the memory
+func (p *pool) Release(s string) {
+	p.mtx.RLock()
+	interned, ok := p.pool[s]
+	p.mtx.RUnlock()
+
+	if !ok {
+		return
+	}
+
+	refs := interned.refs.Dec()
+	if refs > 0 {
+		return
+	}
+
+	p.mtx.Lock()
+	defer p.mtx.Unlock()
+	if interned.refs.Load() != 0 {
+		return
+	}
+	delete(p.pool, s)
+}