Implement proper checkpoint statistics for PostgreSQL 17+

- Add postgres_dba_pgvers_17plus version variable to warmup.psql
- Use \if conditionals to handle PostgreSQL 17+ vs <17 differences
- PostgreSQL 17+: Use pg_stat_checkpointer (num_timed, num_requested, buffers_written)
- PostgreSQL <17: Use pg_stat_bgwriter (checkpoints_timed, checkpoints_req, buffers_checkpoint)
- Follow existing SQL code style and version handling patterns
- Maintain all checkpoint statistics across versions

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: NikolayS

sql/0_node.sql

@@ -49,12 +49,41 @@ 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 'Checkpoint Info', 
-  case 
-    when current_setting('server_version_num')::int >= 170000
-    then 'Use pg_stat_checkpointer view for checkpoint statistics (PostgreSQL 17+)'
-    else 'Use pg_stat_bgwriter view for checkpoint statistics (PostgreSQL <17)'
-  end
+\if :postgres_dba_pgvers_17plus
+select 'Checkpoints', (select (num_timed + num_requested)::text from pg_stat_checkpointer)
+union all
+select 'Forced Checkpoints', (
+  select round(100.0 * num_requested::numeric /
+    (nullif(num_timed + num_requested, 0)), 1)::text || '%'
+  from pg_stat_checkpointer
+)
+union all
+select 'Checkpoint MB/sec', (
+  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
+select 'Checkpoints', (select (checkpoints_timed + checkpoints_req)::text from pg_stat_bgwriter)
+union all
+select 'Forced Checkpoints', (
+  select round(100.0 * checkpoints_req::numeric /
+    (nullif(checkpoints_timed + checkpoints_req, 0)), 1)::text || '%'
+  from pg_stat_bgwriter
+)
+union all
+select 'Checkpoint MB/sec', (
+  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
+)
+\endif
 union all
 select repeat('-', 33), repeat('-', 88)
 union all

warmup.psql

@@ -4,6 +4,8 @@
   select 1/0;
 \endif
 
+select current_setting('server_version_num')::integer >= 170000 as postgres_dba_pgvers_17plus \gset
+
 select current_setting('server_version_num')::integer >= 130000 as postgres_dba_pgvers_13plus \gset
 
 select current_setting('server_version_num')::integer >= 100000 as postgres_dba_pgvers_10plus \gset