[PGD 6.2.0] Add degrade statistics documentation

BDR-6925

Author: irionr

product_docs/docs/pgd/6.2/reference/commit-scopes/degrading.mdx

@@ -62,4 +62,34 @@ ALL (left_dc) CAMO DEGRADE ON (timeout=20ms, require_write_lead=true) TO ASYNC
 
 Again, you should set the `timeout` parameter, as the default is `0`. 
 
+## Monitoring degrade events
+
+Degrade events are tracked in the [bdr.stat_commit_scope](/pgd/latest/reference/tables-views-functions/catalogs-visible/#bdrstat_commit_scope) view. Three key metrics provide visibility into degrade behavior:
+
+- **`ndegrades`**: Counts per-transaction degrade events. Each time a backend hits the degrade timeout during commit and successfully degrades that transaction, this counter is incremented. This shows how many individual transactions have experienced degradation.
+
+- **`nconfig_degrades`**: Counts configuration-level state changes to degraded mode. This is incremented when the background worker (manager process) switches the commit scope's shared state to degraded based on node availability checks. This indicates how many times the commit scope configuration itself entered degraded state, which then affects all subsequent transactions until recovered.
+
+- **`last_state_change_time`**: Records the timestamp of the last configuration-level state change (either entering or recovering from degraded state). This helps identify when the commit scope last transitioned between normal and degraded operation, useful for correlating degrade events with other system events or outages.
+
+### Example monitoring query
+
+```sql
+-- View commit scope statistics including degrade events and last state change
+SELECT
+  commit_scope_name,
+  ndegrades,
+  nconfig_degrades,
+  last_state_change_time,
+  CASE
+    WHEN last_state_change_time IS NULL THEN 'never degraded'
+    WHEN age(now(), last_state_change_time) < interval '5 seconds' THEN 'recently changed'
+    ELSE 'stable for ' || age(now(), last_state_change_time)::text
+  END AS state_change_info
+FROM bdr.stat_commit_scope
+WHERE ndegrades > 0 OR nconfig_degrades > 0
+ORDER BY last_state_change_time DESC NULLS LAST;
+```
+
+These metrics together provide complete visibility into both immediate per-transaction fallback and longer-term state management degrade behavior, along with temporal context for troubleshooting.
 

product_docs/docs/pgd/6.2/reference/monitoring/sql.mdx

@@ -367,10 +367,13 @@ Commit scopes are our durability and consistency configuration framework. As suc
 
 Accordingly, these two views show relevant statistics about commit scopes:
 
--   [bdr.stat_commit_scope](/pgd/latest/reference/tables-views-functions/catalogs-visible/#bdrstat_commit_scope) for cumulative statistics for each commit scope.
+-   [bdr.stat_commit_scope](/pgd/latest/reference/tables-views-functions/catalogs-visible/#bdrstat_commit_scope) for cumulative statistics for each commit scope, including degrade event counters (`ndegrades`, `nconfig_degrades`) and the timestamp of the last configuration state change (`last_state_change_time`).
 
 -   [bdr.stat_commit_scope_state](/pgd/latest/reference/tables-views-functions/catalogs-visible/#bdrstat_commit_scope_state) for information about the current use of commit scopes by backend processes.
 
+For more information about monitoring degrade events, see [Monitoring degrade events](/pgd/latest/reference/commit-scopes/degrading/#monitoring-degrade-events).
+
+
 ## Monitoring global locks
 
 The global lock, which is currently used only for DDL replication, is a heavyweight

product_docs/docs/pgd/6.2/reference/tables-views-functions/catalogs-visible.mdx

@@ -953,18 +953,21 @@ A view containing statistics for each commit scope.
 
 #### `bdr.stat_commit_scope` columns
 
-| Column              | Type                     | Description                                                                                                                     |
-| ------------------- | ------------------------ | ------------------------------------------------------------------------------------------------------------------------------- |
-| commit_scope_name   | name                     | Name of the commit scope
-| group_name          | name                     | Name of group for which the commit scope is defined
-| ncalls              | bigint                   | The number of times the commit scope was used
-| ncommits            | bigint                   | The number of successful commits were made with the commit scope
-| naborts             | bigint                   | The number of times the commit scope used was eventually aborted
-| total_commit_time   | double precision         | Total time spent committing using the commit scope, in milliseconds
-| min_commit_time     | double precision         | Minimum time spent committing using the commit scope, in milliseconds
-| max_commit_time     | double precision         | Maximum time spend committing using the commit scope, in milliseconds
-| mean_commit_time    | double precision         | Mean time spent committing using the commit scope, in milliseconds
-| stats_reset         | timestamp with time zone | Time at which all statistics in the view were last reset
+| Column                  | Type                     | Description                                                                                                                     |
+| ----------------------- | ------------------------ | ------------------------------------------------------------------------------------------------------------------------------- |
+| commit_scope_name       | name                     | Name of the commit scope
+| group_name              | name                     | Name of group for which the commit scope is defined
+| ncalls                  | bigint                   | The number of times the commit scope was used
+| ncommits                | bigint                   | The number of successful commits were made with the commit scope
+| naborts                 | bigint                   | The number of times the commit scope used was eventually aborted
+| ndegrades               | bigint                   | The number of per-transaction degrade events where a backend hit the degrade timeout during commit
+| nconfig_degrades        | bigint                   | The number of configuration-level state changes to degraded mode by the background worker
+| last_state_change_time  | timestamp with time zone | The timestamp of the last configuration-level state change (entering or recovering from degraded state)
+| total_commit_time       | double precision         | Total time spent committing using the commit scope, in milliseconds
+| min_commit_time         | double precision         | Minimum time spent committing using the commit scope, in milliseconds
+| max_commit_time         | double precision         | Maximum time spend committing using the commit scope, in milliseconds
+| mean_commit_time        | double precision         | Mean time spent committing using the commit scope, in milliseconds
+| stats_reset             | timestamp with time zone | Time at which all statistics in the view were last reset
 
 ### `bdr.stat_commit_scope_state`