Remove DDL functions and use informational messages for PG17+

- Remove CREATE FUNCTION statements (no DDL allowed)
- For PostgreSQL 17+: Show 'See pg_stat_checkpointer (PG17+)' message
- For PostgreSQL <17: Continue using pg_stat_bgwriter normally
- Maintains read-only nature of diagnostic tool

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: NikolayS

sql/0_node.sql

@@ -8,58 +8,6 @@ For Postgres versions older than 10, run this first:
   \set postgres_dba_is_wal_replay_paused pg_is_xlog_replay_paused
 */
 
--- Functions to handle PostgreSQL version differences
-create or replace function pg_checkpoints() returns text language plpgsql as $$
-begin
-  if current_setting('server_version_num')::int >= 170000 then
-    return (select (num_timed + num_requested)::text from pg_stat_checkpointer);
-  else
-    return (select (checkpoints_timed + checkpoints_req)::text from pg_stat_bgwriter);
-  end if;
-end;
-$$;
-
-create or replace function pg_forced_checkpoints() returns text language plpgsql as $$
-begin
-  if current_setting('server_version_num')::int >= 170000 then
-    return (
-      select round(100.0 * num_requested::numeric /
-        (nullif(num_timed + num_requested, 0)), 1)::text || '%'
-      from pg_stat_checkpointer
-    );
-  else
-    return (
-      select round(100.0 * checkpoints_req::numeric /
-        (nullif(checkpoints_timed + checkpoints_req, 0)), 1)::text || '%'
-      from pg_stat_bgwriter
-    );
-  end if;
-end;
-$$;
-
-create or replace function pg_checkpoint_mbps() returns text language plpgsql as $$
-begin
-  if current_setting('server_version_num')::int >= 170000 then
-    return (
-      select round((nullif(buffers_written::numeric, 0) /
-        ((1024.0 * 1024 /
-          (current_setting('block_size')::numeric))
-            * extract('epoch' from now() - stats_reset)
-        ))::numeric, 6)::text
-      from pg_stat_checkpointer
-    );
-  else
-    return (
-      select round((nullif(buffers_checkpoint::numeric, 0) /
-        ((1024.0 * 1024 /
-          (current_setting('block_size')::numeric))
-            * extract('epoch' from now() - stats_reset)
-        ))::numeric, 6)::text
-      from pg_stat_bgwriter
-    );
-  end if;
-end;
-$$;
 
 with data as (
   select s.*
@@ -101,11 +49,40 @@ select 'Started At', pg_postmaster_start_time()::timestamptz(0)::text
 union all
 select 'Uptime', (now() - pg_postmaster_start_time())::interval(0)::text
 union all
-select 'Checkpoints', pg_checkpoints()
+select
+  'Checkpoints',
+  case 
+    when current_setting('server_version_num')::int >= 170000
+    then 'See pg_stat_checkpointer (PG17+)'
+    else (select (checkpoints_timed + checkpoints_req)::text from pg_stat_bgwriter)
+  end
 union all
-select 'Forced Checkpoints', pg_forced_checkpoints()
+select
+  'Forced Checkpoints',
+  case 
+    when current_setting('server_version_num')::int >= 170000
+    then 'See pg_stat_checkpointer (PG17+)'
+    else (
+      select round(100.0 * checkpoints_req::numeric /
+        (nullif(checkpoints_timed + checkpoints_req, 0)), 1)::text || '%'
+      from pg_stat_bgwriter
+    )
+  end
 union all
-select 'Checkpoint MB/sec', pg_checkpoint_mbps()
+select
+  'Checkpoint MB/sec',
+  case 
+    when current_setting('server_version_num')::int >= 170000
+    then 'See pg_stat_checkpointer (PG17+)'
+    else (
+      select round((nullif(buffers_checkpoint::numeric, 0) /
+        ((1024.0 * 1024 /
+          (current_setting('block_size')::numeric))
+            * extract('epoch' from now() - stats_reset)
+        ))::numeric, 6)::text
+      from pg_stat_bgwriter
+    )
+  end
 union all
 select repeat('-', 33), repeat('-', 88)
 union all