From 19bcbc7d9d0b937fda66aa1f3f9290c36dc99f4d Mon Sep 17 00:00:00 2001
From: "Andrei V. Lepikhov" <lepihov@gmail.com>
Date: Wed, 10 Dec 2025 15:33:31 +0100
Subject: [PATCH] Simplify the Z0DAN add_node process.

Now, each apply progress HTAB entry contains tangled values of
remote_commit_lsn and remote_commit_ts columns (see handle_commit). So, when
extracting data from the progress view, we can use any of these numbers, and
using LSN streamlines the check_commit_timestamp_and_advance_slot procedure:
we can directly point to the correct WAL record, avoiding the expensive
get_lsn_from_commit_ts() call.

So, replace the expensive search for the proper LSN with direct picking of
a specific WAL record.

TODO:
Further commits should also change the Python version. And consequently,
remove the function get_lsn_from_commit_ts() from the extension altogether.
---
 samples/Z0DAN/zodan.sql | 33 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/samples/Z0DAN/zodan.sql b/samples/Z0DAN/zodan.sql
index 38baba40..7a14ec37 100644
--- a/samples/Z0DAN/zodan.sql
+++ b/samples/Z0DAN/zodan.sql
@@ -2142,7 +2142,7 @@ CREATE OR REPLACE PROCEDURE spock.check_commit_timestamp_and_advance_slot(
 ) LANGUAGE plpgsql AS $$
 DECLARE
     rec RECORD;
-    commit_ts timestamp;
+	start_point record;
     slot_name text;
     dbname text;
     remotesql text;
@@ -2159,16 +2159,18 @@ BEGIN
     FOR rec IN SELECT * FROM temp_spock_nodes WHERE node_name != src_node_name AND node_name != new_node_name LOOP
         -- Check commit timestamp for lag from "other" node to new node
         BEGIN
-            remotesql := format('SELECT commit_timestamp FROM spock.lag_tracker WHERE origin_name = %L AND receiver_name = %L',
-                               rec.node_name, new_node_name);
+            remotesql := format('SELECT commit_lsn, commit_timestamp
+								 FROM spock.lag_tracker
+								 WHERE origin_name = %L AND receiver_name = %L',
+                                rec.node_name, new_node_name);
             IF verb THEN
                 RAISE NOTICE '    Remote SQL for commit timestamp check: %', remotesql;
             END IF;
 
-            SELECT * FROM dblink(new_node_dsn, remotesql) AS t(ts timestamp) INTO commit_ts;
+            SELECT * FROM dblink(new_node_dsn, remotesql) AS t(lsn pg_lsn, ts timestamp) INTO start_point;
 
-            IF commit_ts IS NOT NULL THEN
-                RAISE NOTICE '    OK: %', rpad('Found commit timestamp for ' || rec.node_name || '->' || new_node_name || ': ' || commit_ts, 120, ' ');
+            IF start_point.ts IS NOT NULL THEN
+                RAISE NOTICE '    OK: %', rpad('Found commit timestamp for ' || rec.node_name || '->' || new_node_name || ': ' || start_point.ts, 120, ' ');
             ELSE
                 RAISE NOTICE '    - %', rpad('No commit timestamp found for ' || rec.node_name || '->' || new_node_name, 120, ' ');
                 CONTINUE;
@@ -2205,7 +2207,6 @@ BEGIN
 
             DECLARE
                 current_lsn pg_lsn;
-                target_lsn pg_lsn;
             BEGIN
                 SELECT * FROM dblink(rec.dsn, remotesql) AS t(lsn pg_lsn) INTO current_lsn;
 
@@ -2214,31 +2215,23 @@ BEGIN
                     CONTINUE;
                 END IF;
 
-                -- Get target LSN from commit timestamp
-                remotesql := format('SELECT spock.get_lsn_from_commit_ts(%L, %L::timestamp)', slot_name, commit_ts);
-                IF verb THEN
-                    RAISE NOTICE '    Remote SQL for LSN lookup: %', remotesql;
-                END IF;
-
-                SELECT * FROM dblink(rec.dsn, remotesql) AS t(lsn pg_lsn) INTO target_lsn;
-
-                IF target_lsn IS NULL OR target_lsn <= current_lsn THEN
-                    RAISE NOTICE '    - Slot % already at or beyond target LSN (current: %, target: %)', slot_name, current_lsn, target_lsn;
+                IF start_point.lsn IS NULL OR start_point.lsn <= current_lsn THEN
+                    RAISE NOTICE '    - Slot % already at or beyond target LSN (current: %, target: %)', slot_name, current_lsn, start_point.lsn;
                     CONTINUE;
                 END IF;
 
                 -- Advance the slot
-                remotesql := format('SELECT pg_replication_slot_advance(%L, %L::pg_lsn)', slot_name, target_lsn);
+                remotesql := format('SELECT pg_replication_slot_advance(%L, %L::pg_lsn)', slot_name, start_point.lsn);
                 IF verb THEN
                     RAISE NOTICE '    Remote SQL for slot advancement: %', remotesql;
                 END IF;
 
                 PERFORM * FROM dblink(rec.dsn, remotesql) AS t(result text);
-                RAISE NOTICE '    OK: %', rpad('Advanced slot ' || slot_name || ' from ' || current_lsn || ' to ' || target_lsn, 120, ' ');
+                RAISE NOTICE '    OK: %', rpad('Advanced slot ' || slot_name || ' from ' || current_lsn || ' to ' || start_point.lsn, 120, ' ');
             END;
         EXCEPTION
             WHEN OTHERS THEN
-                RAISE NOTICE '    ✗ %', rpad('Advancing slot ' || slot_name || ' to timestamp ' || commit_ts || ' (error: ' || SQLERRM || ')', 120, ' ');
+                RAISE NOTICE '    ✗ %', rpad('Advancing slot ' || slot_name || ' to timestamp ' || start_point.ts || ' (error: ' || SQLERRM || ')', 120, ' ');
                 -- Continue with other nodes even if this one fails
         END;
     END LOOP;