fix Postgresql replication stat metrics to include replication prefix (#20316)

* fix Postgresql replication stat metrics to include replication prefix

* added changelog

* fix postgres replication lag metrics

* fix postgres replication lag metrics

* remove 20316.fixed.1 changelog entry

Author: shreesampath

postgres/changelog.d/20316.fixed

@@ -0,0 +1 @@
+fix Postgresql replication stat metrics to include `replication.` prefix

postgres/datadog_checks/postgres/util.py

@@ -391,9 +391,10 @@ def get_list_chunks(lst, n):
     pg_stat_replication.client_addr,
     pg_stat_replication_slot.slot_name,
     pg_stat_replication_slot.slot_type,
+    GREATEST (0, age(pg_stat_replication.backend_xmin)) as backend_xmin_age,
     GREATEST (0, EXTRACT(epoch from pg_stat_replication.write_lag)) as write_lag,
-    GREATEST (0, EXTRACT(epoch from pg_stat_replication.replay_lag)) AS replay_lag,
-    GREATEST (0, age(pg_stat_replication.backend_xmin)) AS backend_xmin_age
+    GREATEST (0, EXTRACT(epoch from pg_stat_replication.flush_lag)) as flush_lag,
+    GREATEST (0, EXTRACT(epoch from pg_stat_replication.replay_lag)) AS replay_lag
 FROM pg_stat_replication as pg_stat_replication
 LEFT JOIN pg_replication_slots as pg_stat_replication_slot
 ON pg_stat_replication.pid = pg_stat_replication_slot.active_pid;
@@ -405,9 +406,10 @@ def get_list_chunks(lst, n):
         {'name': 'wal_client_addr', 'type': 'tag'},
         {'name': 'slot_name', 'type': 'tag_not_null'},
         {'name': 'slot_type', 'type': 'tag_not_null'},
-        {'name': 'wal_write_lag', 'type': 'gauge'},
-        {'name': 'wal_flush_lag', 'type': 'gauge'},
-        {'name': 'wal_replay_lag', 'type': 'gauge'},
+        {'name': 'replication.backend_xmin_age', 'type': 'gauge'},
+        {'name': 'replication.wal_write_lag', 'type': 'gauge'},
+        {'name': 'replication.wal_flush_lag', 'type': 'gauge'},
+        {'name': 'replication.wal_replay_lag', 'type': 'gauge'},
     ],
 }