Hot reload to override individual metrics

collector/cache.go

@@ -8,7 +8,7 @@ import (
 	"time"
 )
 
-func NewMetricsCache(metrics []*Metric) *MetricsCache {
+func NewMetricsCache(metrics map[string]*Metric) *MetricsCache {
 	c := map[*Metric]*MetricCacheRecord{}
 
 	for _, metric := range metrics {

collector/collector.go

@@ -252,7 +252,7 @@ func (e *Exporter) scrapeDatabase(ch chan<- prometheus.Metric, errChan chan<- er
 	e.logger.Debug("Successfully pinged Oracle database: "+maskDsn(d.Config.URL), "database", d.Name)
 
 	metricsToScrape := 0
-	for _, metric := range e.metricsToScrape.Metric {
+	for _, metric := range e.metricsToScrape {
 		metric := metric //https://golang.org/doc/faq#closures_and_goroutines
 		isScrapeMetric := e.isScrapeMetric(tick, metric, d)
 		metricsToScrape++
@@ -324,7 +324,7 @@ func (e *Exporter) scrapeDatabase(ch chan<- prometheus.Metric, errChan chan<- er
 
 func (e *Exporter) scrape(ch chan<- prometheus.Metric, tick *time.Time) {
 	e.totalScrapes.Inc()
-	errChan := make(chan error, len(e.metricsToScrape.Metric)*len(e.databases))
+	errChan := make(chan error, len(e.metricsToScrape)*len(e.databases))
 	begun := time.Now()
 	if e.checkIfMetricsChanged() {
 		e.reloadMetrics()
@@ -529,7 +529,7 @@ func (e *Exporter) generatePrometheusMetrics(d *Database, parse func(row map[str
 
 func (e *Exporter) initCache() {
 	for _, d := range e.databases {
-		d.initCache(e.metricsToScrape.Metric)
+		d.initCache(e.metricsToScrape)
 	}
 }
 

collector/data_loader.go

@@ -14,12 +14,8 @@ import (
 )
 
 func (e *Exporter) reloadMetrics() {
-	// Truncate metricsToScrape
-	e.metricsToScrape.Metric = []*Metric{}
-
-	// Load default metrics
-	defaultMetrics := e.DefaultMetrics()
-	e.metricsToScrape.Metric = defaultMetrics.Metric
+	// reload default metrics
+	e.metricsToScrape = e.DefaultMetrics()
 
 	// If custom metrics, load it
 	if len(e.CustomMetricsFiles()) > 0 {
@@ -32,15 +28,22 @@ func (e *Exporter) reloadMetrics() {
 			} else {
 				e.logger.Info("Successfully loaded custom metrics from " + _customMetrics)
 			}
-
-			e.metricsToScrape.Metric = append(e.metricsToScrape.Metric, metrics.Metric...)
+			// Merge custom metrics into default metrics.
+			// Any collisions (by ID) will overwrite the old metric value.
+			e.merge(metrics)
 		}
 	} else {
 		e.logger.Debug("No custom metrics defined.")
 	}
 	e.initCache()
 }
 
+func (e *Exporter) merge(metrics *Metrics) {
+	for _, metric := range metrics.Metric {
+		e.metricsToScrape[metric.ID()] = metric
+	}
+}
+
 func loadYamlMetricsConfig(_metricsFileName string, metrics *Metrics) error {
 	yamlBytes, err := os.ReadFile(_metricsFileName)
 	if err != nil {

collector/database.go

@@ -98,7 +98,7 @@ func NewDatabase(logger *slog.Logger, dbname string, dbconfig DatabaseConfig) *D
 }
 
 // initCache resets the metrics cached. Used on startup and when metrics are reloaded.
-func (d *Database) initCache(metrics []*Metric) {
+func (d *Database) initCache(metrics map[string]*Metric) {
 	d.MetricsCache = NewMetricsCache(metrics)
 }
 

collector/default_metrics.go

@@ -17,19 +17,19 @@ import (
 var defaultMetricsToml string
 
 // DefaultMetrics is a somewhat hacky way to load the default metrics
-func (e *Exporter) DefaultMetrics() Metrics {
+func (e *Exporter) DefaultMetrics() map[string]*Metric {
 	var metricsToScrape Metrics
 	if e.Metrics.Default != "" {
 		if err := loadMetricsConfig(filepath.Clean(e.Metrics.Default), &metricsToScrape); err != nil {
 			e.logger.Error(fmt.Sprintf("there was an issue while loading specified default metrics file at: "+e.Metrics.Default+", proceeding to run with default metrics."),
 				"error", err)
 		}
-		return metricsToScrape
+		return metricsToScrape.toMap()
 	}
 
 	if _, err := toml.Decode(defaultMetricsToml, &metricsToScrape); err != nil {
 		e.logger.Error("failed to load default metrics", "error", err)
 		panic(errors.New("Error while loading " + defaultMetricsToml))
 	}
-	return metricsToScrape
+	return metricsToScrape.toMap()
 }

collector/metrics.go

@@ -112,3 +112,11 @@ func (m *Metric) IsEnabledForDatabase(d *Database) bool {
 	}
 	return false
 }
+
+func (metrics Metrics) toMap() map[string]*Metric {
+	m := map[string]*Metric{}
+	for _, metric := range metrics.Metric {
+		m[metric.ID()] = metric
+	}
+	return m
+}

collector/types.go

@@ -15,7 +15,7 @@ import (
 type Exporter struct {
 	*MetricsConfiguration
 	mu              *sync.Mutex
-	metricsToScrape Metrics
+	metricsToScrape map[string]*Metric
 	duration, error prometheus.Gauge
 	totalScrapes    prometheus.Counter
 	scrapeErrors    *prometheus.CounterVec

site/docs/configuration/custom-metrics.md

@@ -23,6 +23,10 @@ metrics:
 
 You may also use `--custom.metrics` flag followed by a comma separated list of TOML or YAML files, or export `CUSTOM_METRICS` variable environment (`export CUSTOM_METRICS=my-custom-metrics.toml,my-other-custom-metrics.toml`)
 
+### Metric Hot Reload
+
+The exporter watches for changes in custom metrics. When these files change, the exporter hot reloads the metrics definition, and serves the new metrics on the next scrape.
+
 ### Metric Schema
 
 Metrics files must contain a series of `[[metric]]` definitions, in TOML, or the equivalent definition in a YAML file. Each metric definition must follow the exporter's metric schema:
@@ -123,6 +127,40 @@ oracledb_test_value_2 2
 You can find [working examples](https://github.com/oracle/oracle-db-appdev-monitoring/blob/main/custom-metrics-example/custom-metrics.toml) of custom metrics for slow queries, big queries and top 100 tables.
 An example of [custom metrics for Transacational Event Queues](https://github.com/oracle/oracle-db-appdev-monitoring/blob/main/custom-metrics-example/txeventq-metrics.toml) is also provided.
 
+#### Override Existing, Individual Metrics
+
+You may override properties for existing metrics by supplying a new, custom metric definition with the same `context` and `metricsdesc` values. For example, if you have an existing metric like so:
+
+```toml
+[[metric]]
+context = "my_default_metric"
+metricsdesc = { value_1 = "Simple example returning always 1.", value_2 = "Same but returning always 2." }
+request = "SELECT 1 as value_1, 2 as value_2 FROM DUAL"
+```
+
+You can redefine this metric in a custom metrics file to change any properties other than `context` or `metricsdesc`. For example, overriding the previous metric with `labels`, `scrapeinterval`, and `querytimeout` properties:
+
+```toml
+[[metric]]
+context = "my_default_metric"
+metricsdesc = { value_1 = "Simple example returning always 1.", value_2 = "Same but returning always 2." }
+labels = [ "label_1", "label_2" ]
+request = "SELECT 1 as value_1, 2 as value_2 FROM DUAL"
+scrapeinterval = "30s"
+querytimeout = "10s"
+```
+
+Then, provide any metrics overrides as custom metrics files in the [exporter configuration file](config-file.md):
+
+```yaml
+metrics:
+  ## Paths to any custom metrics files
+  custom:
+    - my-custom-metrics.toml
+```
+
+If any metric appears more than once in the custom metrics file list, the metric definition in the last file provided takes precedence.
+
 ### YAML Metrics
 
 Metrics may be defined with YAML instead of TOML. YAML metric field names correspond to TOML metric field names.

site/docs/releases/changelog.md

@@ -13,6 +13,7 @@ Our current priorities to support metrics for advanced database features and use
 
 - Updated project dependencies.
 - Standardize multi-arch builds and document supported database versions.
+- The metrics override capability is extended, allowing users to redefine individual existing metrics in custom metrics files. This allows users to modify individual default metrics without wholly replacing the default metrics file. 
 - If the exporter fails to connect to a database due to invalid or locked credentials (ORA-01017 or ORA-28000 errors), that database configuration will be invalidated and the exporter will not attempt to re-establish the database connection. Other databases will continue to be scraped.
 - Metrics with an empty databases array (`databases = []`) are now considered disabled, and will not be scraped.
 - Increased the default query timeout for the `top_sql` metric to 10 seconds (previously 5 seconds).