Run the query for specific database version if provided from yml file.

By default query will run on all the databases if "runonserver" is not provided.

If user want the query to be run on multiple database versions, use below string.
  runonserver: "9.5, 9.6"

Example yml file as below. ( e.g. below query will run only on database version 9.5 )

pg_replication:
  query: "SELECT EXTRACT(EPOCH FROM (now() - pg_last_xact_replay_timestamp())) as lag"
  master: true
  runonserver: "9.5"
  metrics:
    - lag:
        usage: "GAUGE"
        description: "Replication lag behind master in seconds"

Author: neel5481

cmd/postgres_exporter/postgres_exporter.go

@@ -115,6 +115,7 @@ type UserQuery struct {
 	Metrics      []Mapping `yaml:"metrics"`
 	Master       bool      `yaml:"master"`        // Querying only for master database
 	CacheSeconds uint64    `yaml:"cache_seconds"` // Number of seconds to cache the namespace result metrics for.
+	RunOnServer  string    `yaml:"runonserver"`   // Querying to run on which server version
 }
 
 // nolint: golint
@@ -155,6 +156,7 @@ type intermediateMetricMap struct {
 	columnMappings map[string]ColumnMapping
 	master         bool
 	cacheSeconds   uint64
+	runonserver    string
 }
 
 // MetricMapNamespace groups metric maps under a shared set of labels.
@@ -163,6 +165,7 @@ type MetricMapNamespace struct {
 	columnMappings map[string]MetricMap // Column mappings in this namespace
 	master         bool                 // Call query only for master database
 	cacheSeconds   uint64               // Number of seconds this metric namespace can be cached. 0 disables.
+	runonserver    string               // Run the query on which server version
 }
 
 // MetricMap stores the prometheus metric description which a given column will
@@ -221,6 +224,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
+		"all",
 	},
 	"pg_stat_database": {
 		map[string]ColumnMapping{
@@ -246,6 +250,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
+		"all",
 	},
 	"pg_stat_database_conflicts": {
 		map[string]ColumnMapping{
@@ -259,6 +264,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
+		"all",
 	},
 	"pg_locks": {
 		map[string]ColumnMapping{
@@ -268,6 +274,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
+		"all",
 	},
 	"pg_stat_replication": {
 		map[string]ColumnMapping{
@@ -314,6 +321,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
+		"all",
 	},
 	"pg_stat_archiver": {
 		map[string]ColumnMapping{
@@ -328,6 +336,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
+		"all",
 	},
 	"pg_stat_activity": {
 		map[string]ColumnMapping{
@@ -338,6 +347,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
+		"all",
 	},
 }
 
@@ -494,6 +504,7 @@ func parseUserQueries(content []byte) (map[string]intermediateMetricMap, map[str
 		return nil, nil, err
 	}
 
+
 	// Stores the loaded map representation
 	metricMaps := make(map[string]intermediateMetricMap)
 	newQueryOverrides := make(map[string]string)
@@ -509,6 +520,7 @@ func parseUserQueries(content []byte) (map[string]intermediateMetricMap, map[str
 				columnMappings: newMetricMap,
 				master:         specs.Master,
 				cacheSeconds:   specs.CacheSeconds,
+				runonserver:    specs.RunOnServer,
 			}
 			metricMaps[metric] = metricMap
 		}
@@ -678,7 +690,7 @@ func makeDescMap(pgVersion semver.Version, serverLabels prometheus.Labels, metri
 			}
 		}
 
-		metricMap[namespace] = MetricMapNamespace{variableLabels, thisMap, intermediateMappings.master, intermediateMappings.cacheSeconds}
+		metricMap[namespace] = MetricMapNamespace{variableLabels, thisMap, intermediateMappings.master, intermediateMappings.cacheSeconds, intermediateMappings.runonserver}
 	}
 
 	return metricMap
@@ -835,6 +847,8 @@ type Server struct {
 	db     *sql.DB
 	labels prometheus.Labels
 	master bool
+	runonserver string
+	serverversion string
 
 	// Last version used to calculate metric map. If mismatch on scrape,
 	// then maps are recalculated.
@@ -880,6 +894,7 @@ func NewServer(dsn string, opts ...ServerOpt) (*Server, error) {
 	s := &Server{
 		db:     db,
 		master: false,
+		runonserver: "all",
 		labels: prometheus.Labels{
 			serverLabelName: fingerprint,
 		},
@@ -1327,6 +1342,12 @@ func queryNamespaceMappings(ch chan<- prometheus.Metric, server *Server) map[str
 			continue
 		}
 
+		// check if the query is to be run on specific server version or not
+		if len(mapping.runonserver) > 0 && !strings.Contains(mapping.runonserver, "all") && !strings.Contains(server.serverversion, mapping.runonserver) {
+			log.Debugln("Query skipped for database version: [%s] as it should be run on database server version: [%s]", server.serverversion, mapping.runonserver)
+			continue
+		}
+
 		scrapeMetric := false
 		// Check if the metric is cached
 		server.cacheMtx.Lock()
@@ -1415,6 +1436,7 @@ func (e *Exporter) checkMapVersions(ch chan<- prometheus.Metric, server *Server)
 		}
 
 		server.lastMapVersion = semanticVersion
+		server.serverversion = semanticVersion.String()
 
 		if e.userQueriesPath != "" {
 			// Clear the metric while a reload is happening