[!] add Grafana v12 dashboards for Prometheus data source (#933)

* [!] add Grafana v12 dashboards for Prometheus data source

Add Prometheus dashboard equivalents for PostgreSQL monitoring

Created a comprehensive set of 12 Grafana dashboards that use Prometheus as
the data source, providing equivalent functionality to the existing PostgreSQL
dashboards. The new dashboards translate SQL queries to PromQL while maintaining
all monitoring capabilities.

New dashboards include:
- Global database overview with connections, QPS, TPS, and query runtime
- Query performance analysis with top queries by time and calls
- Table activity monitoring with scans, modifications, and sizes
- Replication monitoring with WAL activity and status tracking
- Performance recommendations for indexes, queries, and configuration
- Stored procedures monitoring with call statistics and performance
- Statement analysis dashboards for calls and execution time
- System resource monitoring for CPU, memory, and disk usage

All dashboards feature:
- Proper PromQL translations using rate() functions for counters
- Consistent template variables for database selection and time intervals
- Table transformations to join metrics by common identifiers
- Appropriate units and thresholds for monitoring PostgreSQL systems

This enables users who prefer Prometheus as their metrics backend to have
the same comprehensive PostgreSQL monitoring capabilities that were previously
only available with direct PostgreSQL connections.

* [-] fix "Connections Overview" panel in "Global Overview dashboard"

* [+] enable both dashboard sets Postgres and Prometheus in docker compose

* [-] fix Connections Overview promql

Author: pashagolub

docker/compose.grafana.yml

@@ -6,7 +6,7 @@ services:
     user: "0:0"
     environment:
       GF_AUTH_ANONYMOUS_ENABLED: true
-      GF_DASHBOARDS_DEFAULT_HOME_DASHBOARD_PATH: /var/lib/grafana/dashboards/1-global-db-overview.json
+      GF_DASHBOARDS_DEFAULT_HOME_DASHBOARD_PATH: /var/lib/grafana/dashboards/postgres/1-global-db-overview.json
       GF_INSTALL_PLUGINS: marcusolsson-treemap-panel
       GF_AUTH_ANONYMOUS_ORG_ROLE: Admin
       # GF_FEATURE_TOGGLES_ENABLE: dashboardNewLayouts
@@ -17,14 +17,10 @@ services:
       - "../grafana/dashboards.yml:/etc/grafana/provisioning/dashboards/pgwatch_dashboards.yml"
       # Uncomment the datasource version you want to use
       - "../grafana/postgres_datasource.yml:/etc/grafana/provisioning/datasources/postgres_datasource.yml"
-      # - "../grafana/prometheus_datasource.yml:/etc/grafana/provisioning/datasources/prometheus_datasource.yml"
+      - "../grafana/prometheus_datasource.yml:/etc/grafana/provisioning/datasources/prometheus_datasource.yml"
       # Uncomment the dashboard version you want to use and comment out the other one.
-      # - "../grafana/postgres/v10:/var/lib/grafana/dashboards"
-      # - "../grafana/postgres/v11:/var/lib/grafana/dashboards"
-      - "../grafana/postgres/v12:/var/lib/grafana/dashboards"
-      # - "../grafana/prometheus/v10:/var/lib/grafana/dashboards"
-      # - "../grafana/prometheus/v11:/var/lib/grafana/dashboards"
-      # - "../grafana/prometheus/v12:/var/lib/grafana/dashboards"
+      - "../grafana/postgres/v12:/var/lib/grafana/dashboards/postgres"
+      - "../grafana/prometheus/v12:/var/lib/grafana/dashboards/prometheus"
     depends_on:
       postgres:
         condition: service_healthy

grafana/dashboards.yml

@@ -1,11 +1,24 @@
 apiVersion: 1
 
 providers:
-- name: 'default'
+- name: 'postgres-dashboards'
   orgId: 1
-  folder: ''
+  folder: 'pgwatch (postgres)'
   type: 'file'
   disableDeletion: false
-  updateIntervalSeconds: 10 #how often Grafana will scan for changed dashboards
+  allowUiUpdates: true
+  editable: true
+  updateIntervalSeconds: 10
   options:
-    path: /var/lib/grafana/dashboards
+    path: /var/lib/grafana/dashboards/postgres
+
+- name: 'prometheus-dashboards'
+  orgId: 1
+  folder: 'pgwatch (prometheus)'
+  type: 'file'
+  disableDeletion: false
+  allowUiUpdates: true
+  editable: true
+  updateIntervalSeconds: 10
+  options:
+    path: /var/lib/grafana/dashboards/prometheus

grafana/postgres/v12/1-global-db-overview.json

@@ -32,7 +32,7 @@
         "type": "grafana-postgresql-datasource",
         "uid": "pgwatch-metrics"
       },
-      "description": "- Total number of sessions established to database(s). \n- Number of database sessions that were terminated because connection to the client was lost.\n- Number of database sessions that were terminated by fatal errors.\n- Number of database sessions that were terminated by operator intervention.",
+      "description": "Number of new database sessions established per monitored source over time. Each line represents a different monitored database/source.",
       "fieldConfig": {
         "defaults": {
           "color": {
@@ -114,9 +114,9 @@
       "targets": [
         {
           "editorMode": "code",
-          "format": "table",
+          "format": "time_series",
           "rawQuery": true,
-          "rawSql": "with sessions as (\r\n  SELECT \r\n  $__timeGroup(time, $agg_interval),\r\n  (data->>'sessions')::int8 as sessions,\r\n  lag((data->>'sessions')::int8) over w as lag_sessions,\r\n  (data->>'sessions_abandoned')::int8 as sessions_abandoned,\r\n  lag((data->>'sessions_abandoned')::int8) over w as lag_sessions_abandoned,\r\n  (data->>'sessions_fatal')::int8 as sessions_fatal,\r\n  lag((data->>'sessions_fatal')::int8) over w as lag_sessions_fatal,\r\n  (data->>'sessions_killed')::int8 as sessions_killed,\r\n  lag((data->>'sessions_killed')::int8) over w as lag_sessions_killed\r\nfrom db_stats \r\nwhere dbname in ($dbname) and $__timeFilter(time)\r\nwindow w as (order by time)\r\n)\r\nselect \r\n  time,\r\n  sum(sessions)-sum(lag_sessions) as established,\r\n  sum(sessions_abandoned)-sum(lag_sessions_abandoned) as abandoned,\r\n  sum(sessions_fatal)-sum(lag_sessions_fatal) as fatal,\r\n  sum(sessions_killed)-sum(lag_sessions_killed) as killed\r\nfrom sessions \r\ngroup by time\r\norder by 1",
+          "rawSql": "with session_changes as (\r\n  SELECT \r\n  dbname,\r\n  time,\r\n  coalesce((data->>'sessions')::int8 - lag((data->>'sessions')::int8) over w, 0) as established\r\nfrom db_stats \r\nwhere dbname in ($dbname) and $__timeFilter(time)\r\nwindow w as (partition by dbname order by time)\r\n)\r\nselect \r\n  $__timeGroup(time, $agg_interval),\r\n  sum(established) as value,\r\n  dbname as metric\r\nfrom session_changes\r\ngroup by 1, dbname\r\norder by 1, dbname",
           "refId": "A",
           "sql": {
             "columns": [