tsdb: use float64 for retention percentage

The retention.percentage config field was typed as uint, which silently
truncated fractional values. Setting percentage: 1.5 in prometheus.yml
resulted in a retention of 1%, with no warning or error.

Remove the redundant MaxPercentage > 100 clamp in main.go; the config
UnmarshalYAML already returns an error for out-of-range values before
this code is reached.

Signed-off-by: Julien Pivotto <291750+roidelapluie@users.noreply.github.com>

cmd/prometheus/main.go

@@ -797,16 +797,12 @@ func main() {
 			logger.Warn("Time retention value is too high. Limiting to: " + y.String())
 		}
 
-		if cfg.tsdb.MaxPercentage > 100 {
-			cfg.tsdb.MaxPercentage = 100
-			logger.Warn("Percentage retention value is too high. Limiting to: 100%")
-		}
 		if cfg.tsdb.MaxPercentage > 0 {
 			if cfg.tsdb.MaxBytes > 0 {
 				logger.Warn("storage.tsdb.retention.size is ignored, because storage.tsdb.retention.percentage is specified")
 			}
 			if prom_runtime.FsSize(localStoragePath) == 0 {
-				fmt.Fprintln(os.Stderr, fmt.Errorf("unable to detect total capacity of metric storage at %s, please disable retention percentage (%d%%)", localStoragePath, cfg.tsdb.MaxPercentage))
+				fmt.Fprintln(os.Stderr, fmt.Errorf("unable to detect total capacity of metric storage at %s, please disable retention percentage (%g%%)", localStoragePath, cfg.tsdb.MaxPercentage))
 				os.Exit(2)
 			}
 		}
@@ -2014,7 +2010,7 @@ type tsdbOptions struct {
 	MaxBlockChunkSegmentSize       units.Base2Bytes
 	RetentionDuration              model.Duration
 	MaxBytes                       units.Base2Bytes
-	MaxPercentage                  uint
+	MaxPercentage                  float64
 	NoLockfile                     bool
 	WALCompressionType             compression.Type
 	HeadChunksWriteQueueSize       int

config/config.go

@@ -1111,7 +1111,7 @@ type TSDBRetentionConfig struct {
 	Size units.Base2Bytes `yaml:"size,omitempty"`
 
 	// Maximum percentage of disk used for TSDB storage.
-	Percentage uint `yaml:"percentage,omitempty"`
+	Percentage float64 `yaml:"percentage,omitempty"`
 }
 
 // UnmarshalYAML implements the yaml.Unmarshaler interface.
@@ -1124,7 +1124,7 @@ func (t *TSDBRetentionConfig) UnmarshalYAML(unmarshal func(any) error) error {
 	if t.Size < 0 {
 		return fmt.Errorf("'storage.tsdb.retention.size' must be greater than or equal to 0, got %v", t.Size)
 	}
-	if t.Percentage > 100 {
+	if t.Percentage < 0 || t.Percentage > 100 {
 		return fmt.Errorf("'storage.tsdb.retention.percentage' must be in the range [0, 100], got %v", t.Percentage)
 	}
 	return nil

config/config_test.go

@@ -2640,7 +2640,7 @@ var expectedErrors = []struct {
 	},
 	{
 		filename: "tsdb_retention_percentage_negative.bad.yml",
-		errMsg:   "cannot unmarshal !!int `-1` into uint",
+		errMsg:   "'storage.tsdb.retention.percentage' must be in the range [0, 100]",
 	},
 }
 
@@ -2652,6 +2652,12 @@ func TestBadConfigs(t *testing.T) {
 	}
 }
 
+func TestTSDBRetentionPercentageFloat(t *testing.T) {
+	c, err := LoadFile("testdata/tsdb_retention_percentage_float.good.yml", false, promslog.NewNopLogger())
+	require.NoError(t, err)
+	require.Equal(t, 0.5, c.StorageConfig.TSDBConfig.Retention.Percentage)
+}
+
 func TestBadStaticConfigsYML(t *testing.T) {
 	content, err := os.ReadFile("testdata/static_config.bad.yml")
 	require.NoError(t, err)

config/testdata/tsdb_retention_percentage_float.good.yml

@@ -0,0 +1,4 @@
+storage:
+  tsdb:
+    retention:
+      percentage: 0.5

tsdb/db.go

@@ -130,7 +130,7 @@ type Options struct {
 	// Maximum % of disk space to use for blocks to be retained.
 	// 0 or less means disabled.
 	// If both MaxBytes and MaxPercentage are set, percentage prevails.
-	MaxPercentage uint
+	MaxPercentage float64
 
 	// NoLockfile disables creation and consideration of a lock file.
 	NoLockfile bool
@@ -1105,7 +1105,7 @@ func open(dir string, l *slog.Logger, r prometheus.Registerer, opts *Options, rn
 	db.metrics = newDBMetrics(db, r)
 	maxBytes := max(opts.MaxBytes, 0)
 	db.metrics.maxBytes.Set(float64(maxBytes))
-	db.metrics.maxPercentage.Set(float64(max(opts.MaxPercentage, 0)))
+	db.metrics.maxPercentage.Set(max(opts.MaxPercentage, 0))
 	db.metrics.retentionDuration.Set((time.Duration(opts.RetentionDuration) * time.Millisecond).Seconds())
 
 	// Calling db.reload() calls db.reloadBlocks() which requires cmtx to be locked.
@@ -1295,7 +1295,7 @@ func (db *DB) ApplyConfig(conf *config.Config) error {
 			db.opts.MaxBytes = int64(conf.StorageConfig.TSDBConfig.Retention.Size)
 			db.metrics.maxBytes.Set(float64(db.opts.MaxBytes))
 			db.opts.MaxPercentage = conf.StorageConfig.TSDBConfig.Retention.Percentage
-			db.metrics.maxPercentage.Set(float64(db.opts.MaxPercentage))
+			db.metrics.maxPercentage.Set(db.opts.MaxPercentage)
 			db.retentionMtx.Unlock()
 		}
 	} else {
@@ -1342,7 +1342,7 @@ func (db *DB) getRetentionDuration() int64 {
 }
 
 // getRetentionSettings returns max bytes and max percentage settings in a thread-safe manner.
-func (db *DB) getRetentionSettings() (int64, uint) {
+func (db *DB) getRetentionSettings() (int64, float64) {
 	db.retentionMtx.RLock()
 	defer db.retentionMtx.RUnlock()
 	return db.opts.MaxBytes, db.opts.MaxPercentage
@@ -2018,7 +2018,7 @@ func BeyondSizeRetention(db *DB, blocks []*Block) (deletable map[ulid.ULID]struc
 		if diskSize <= 0 {
 			db.logger.Warn("Unable to retrieve filesystem size of database directory, skip percentage limitation and default to fixed size limitation", "dir", db.dir)
 		} else {
-			maxBytes = int64(uint64(maxPercentage) * diskSize / 100)
+			maxBytes = int64(float64(diskSize) * maxPercentage / 100)
 		}
 	}
 

tsdb/db_test.go

@@ -9663,8 +9663,8 @@ func TestBeyondSizeRetentionWithPercentage(t *testing.T) {
 	db := newTestDB(t, withOpts(opts))
 	require.Zero(t, db.Head().Size())
 
-	blocks := make([]*Block, 0, opts.MaxPercentage+1)
-	for range opts.MaxPercentage {
+	blocks := make([]*Block, 0, int(opts.MaxPercentage)+1)
+	for range int(opts.MaxPercentage) {
 		blocks = append(blocks, &Block{
 			numBytesChunks: numBytesChunks,
 			meta:           BlockMeta{ULID: ulid.Make()},

web/web.go

@@ -268,7 +268,7 @@ type Options struct {
 	TSDBRetentionDuration model.Duration
 	TSDBDir               string
 	TSDBMaxBytes          units.Base2Bytes
-	TSDBMaxPercentage     uint
+	TSDBMaxPercentage     float64
 	LocalStorage          LocalStorage
 	Storage               storage.Storage
 	ExemplarStorage       storage.ExemplarQueryable
@@ -889,7 +889,7 @@ func (h *Handler) runtimeInfo() (api_v1.RuntimeInfo, error) {
 		if status.StorageRetention != "" {
 			status.StorageRetention += " or "
 		}
-		status.StorageRetention = status.StorageRetention + strconv.FormatUint(uint64(tsdbMaxPercentage), 10) + "%"
+		status.StorageRetention = status.StorageRetention + strconv.FormatFloat(tsdbMaxPercentage, 'g', -1, 64) + "%"
 	}
 
 	metrics, err := h.gatherer.Gather()