Use debug severity for messages related when collector unable collect…

… metrics due to Postgres version; Add related changes to docs.

doc/collectors.md

@@ -22,20 +22,20 @@ Index of content:
 
 ### PostgreSQL collectors
 - postgres/activity: activity stats from `pg_stat_activity`
-- postgres/archiver: WAL archiver stats from `pg_stat_archiver`
+- postgres/archiver: WAL archiver stats from `pg_stat_archiver`; **required Postgres 12 or newer**
 - postgres/bgwriter: background writer and checkpointer stats from `pg_stat_bgwriter`
 - postgres/conflicts: recovery conflicts during replication, from `pg_stat_database_conflicts`
 - postgres/databases: databases stats from `pg_stat_databases`
 - postgres/indexes: indexes stats from `pg_stat_user_indexes`, `pg_statio_user_indexes`
 - postgres/functions: functions stats from `pg_stat_user_functions`
 - postgres/locks: activity locks from `pg_locks`
-- postgres/logs: log messages from Postgres log files
+- postgres/logs: log messages from Postgres log files; **required Postgres 10 or newer**
 - postgres/replication: replication stats from `pg_stat_replication`
 - postgres/replication_slots: stats about replication slots from `pg_replication_slots`
 - postgres/statements: statements stats from `pg_stat_statements`
-- postgres/schemas: databases' schemas stats from system catalog
+- postgres/schemas: databases' schemas stats from system catalog; **required Postgres 9.5 or newer**
 - postgres/settings: Postgres settings based on `pg_show_all_settings()`
-- postgres/storage: data files/directories stats 
+- postgres/storage: data files/directories stats; **required Postgres 10 or newer**
 - postgres/tables: tables stats from `pg_stat_user_tables`, `pg_statio_user_tables`
 
 ### Pgbouncer collectors

doc/usage-en.md

@@ -112,12 +112,12 @@ defaults:
     pgbouncer_username: "monitoring"
     pgbouncer_password: "supersecret"
 filters:
-    - diskstats/device:
-      exclude: "^(ram|loop|fd|sr|(h|s|v|xv)d[a-z]|nvme\d+n\d+p)\d+$"
-    - netdev/device:
-      exclude: "docker|virbr"
-    - filesystem/fstype:
-      include: "^(ext3|ext4|xfs|btrfs)$"
+  - diskstats/device:
+    exclude: "^(ram|loop|fd|sr|(h|s|v|xv)d[a-z]|nvme\d+n\d+p)\d+$"
+  - netdev/device:
+    exclude: "docker|virbr"
+  - filesystem/fstype:
+    include: "^(ext3|ext4|xfs|btrfs)$"
 ```
 
 ### Bootstrap and Uninstall modes

internal/collector/config.go

@@ -95,7 +95,7 @@ func NewPostgresServiceConfig(connStr string) (PostgresServiceConfig, error) {
 	}
 
 	if version < PostgresVMinNum {
-		log.Warnf("Postgres version is too old, some collectors functions won't work. Minimum required version is %s.", PostgresVMinStr)
+		log.Warnf("Postgres version is too old, some collectors functions won't work. Minimal required version is %s.", PostgresVMinStr)
 	}
 
 	config.ServerVersionNum = version

internal/collector/postgres_archiver.go

@@ -64,7 +64,7 @@ func (c *postgresWalArchivingCollector) Update(config Config, ch chan<- promethe
 	defer conn.Close()
 
 	if config.ServerVersionNum < PostgresV12 {
-		log.Warnln("[postgres WAL archiver collector]: some system functions are not available, required Postgres 12 or newer")
+		log.Debugln("[postgres WAL archiver collector]: some system functions are not available, required Postgres 12 or newer")
 		return nil
 	}
 

internal/collector/postgres_logs.go

@@ -115,7 +115,7 @@ func (c *postgresLogsCollector) Update(config Config, ch chan<- prometheus.Metri
 	}
 
 	if config.ServerVersionNum < PostgresV10 {
-		log.Infof("[postgres log collector]: some system functions are not available, required Postgres 10 or newer")
+		log.Debugln("[postgres log collector]: some system functions are not available, required Postgres 10 or newer")
 		return nil
 	}
 

internal/collector/postgres_schema.go

@@ -118,7 +118,7 @@ func (c *postgresSchemaCollector) Update(config Config, ch chan<- prometheus.Met
 
 		// Functions below uses queries with casting to regnamespace data type, which is introduced in Postgres 9.5.
 		if config.ServerVersionNum < PostgresV95 {
-			log.Warnln("[postgres schema collector]: some system data types are not available, required Postgres 9.5 or newer")
+			log.Debugln("[postgres schema collector]: some system data types are not available, required Postgres 9.5 or newer")
 			conn.Close()
 			continue
 		}