Rename create_slot_with_progress to read_peer_progress and fix stale comments

The SQL function no longer creates a slot (that moved to the C caller
via replication protocol).  Rename to reflect its actual purpose.

Also fix stale comments referencing advisory locks (removed earlier)
in pause/resume worker functions.

Author: mason-sharp

sql/spock--5.0.6--6.0.0-devel.sql

@@ -40,9 +40,10 @@ RETURNS void
 AS 'MODULE_PATHNAME', 'spock_resume_apply_workers'
 LANGUAGE C VOLATILE;
 
--- Atomically create a replication slot and read spock.progress for all peers.
--- Row 0: lsn + snapshot header.  Rows 1+: one progress entry per peer.
-CREATE FUNCTION spock.create_slot_with_progress(
+-- Read peer progress (ros.remote_lsn) for all peer subscriptions.
+-- Called while apply workers are paused and the slot's snapshot is imported.
+-- Row 0: header (lsn + snapshot placeholder).  Rows 1+: one progress entry per peer.
+CREATE FUNCTION spock.read_peer_progress(
     p_slot_name text,
     p_provider_node_id oid,
     p_subscriber_node_id oid

sql/spock--6.0.0-devel.sql

@@ -121,9 +121,10 @@ CREATE VIEW spock.progress AS
         SELECT oid FROM pg_database WHERE datname = current_database()
       );
 
--- Atomically create a replication slot and read spock.progress for all peers.
--- Row 0: lsn + snapshot header.  Rows 1+: one progress entry per peer.
-CREATE FUNCTION spock.create_slot_with_progress(
+-- Read peer progress (ros.remote_lsn) for all peer subscriptions.
+-- Called while apply workers are paused and the slot's snapshot is imported.
+-- Row 0: header (lsn + snapshot placeholder).  Rows 1+: one progress entry per peer.
+CREATE FUNCTION spock.read_peer_progress(
     p_slot_name text,
     p_provider_node_id oid,
     p_subscriber_node_id oid

src/spock.c

@@ -1156,7 +1156,7 @@ _PG_init(void)
 
 	DefineCustomIntVariable("spock.pause_timeout",
 							"Timeout in seconds for pausing apply workers during slot creation",
-							"Controls how long create_slot_with_progress waits for apply "
+							"Controls how long add_node waits for apply "
 							"workers to reach a between-transaction pause point. Increase "
 							"if add_node fails with a pause timeout under heavy load.",
 							&spock_pause_timeout,

src/spock_apply.c

@@ -432,7 +432,7 @@ begin_replication_step(void)
 	if (!IsTransactionState())
 	{
 		/*
-		 * Check if create_slot_with_progress needs us to pause.  This only
+		 * Check if slot creation (add_node) needs us to pause.  This only
 		 * fires during add_node (a rare operation).  The fast path is a
 		 * single atomic read that almost always sees 0.
 		 *
@@ -989,7 +989,7 @@ handle_commit(StringInfo s)
 	in_remote_transaction = false;
 
 	/*
-	 * If create_slot_with_progress is waiting for us, pause here.  The
+	 * If slot creation (add_node) is waiting for us, pause here.  The
 	 * commit is fully complete (ros.remote_lsn updated, xid cleared),
 	 * so the snapshot and origin will be consistent.
 	 */

src/spock_functions.c

@@ -3322,12 +3322,12 @@ spock_create_sync_event(PG_FUNCTION_ARGS)
 /*
  * spock_pause_apply_workers
  *
- * Pause all apply workers in this database by acquiring an exclusive advisory
- * lock and setting the shared memory flag.  Apply workers check the flag
- * between transactions and block on a shared advisory lock until we release.
+ * Temporarily pause all apply workers in this database during slot creation
+ * for add_node.  Sets a shared memory flag that workers check between
+ * transactions; workers sleep on a ConditionVariable until resumed.
  *
  * After this function returns, all apply workers have finished their current
- * transaction and are blocked, so pg_replication_origin_status reflects only
+ * transaction and are paused, so pg_replication_origin_status reflects only
  * committed state that is visible in any new snapshot.
  */
 Datum
@@ -3402,8 +3402,8 @@ spock_pause_apply_workers(PG_FUNCTION_ARGS)
 /*
  * spock_resume_apply_workers
  *
- * Resume apply workers by clearing the flag and releasing the exclusive
- * advisory lock.
+ * Resume apply workers by clearing the flag and broadcasting on the
+ * ConditionVariable to wake all sleeping workers.
  */
 Datum
 spock_resume_apply_workers(PG_FUNCTION_ARGS)

src/spock_group.c

@@ -737,7 +737,7 @@ spock_group_progress_force_set_list(List *lst)
 		{
 			/*
 			 * Existing LSN >= resume_lsn.  Unconditionally overwrite: the
-			 * value from create_slot_with_progress is authoritative because
+			 * value from read_peer_progress is authoritative because
 			 * it was captured at COPY snapshot time.  The apply worker may
 			 * have advanced past it since then, but any data it applied
 			 * after the snapshot is NOT in the COPY — so the new node must

src/spock_sync.c

@@ -557,7 +557,7 @@ adjust_progress_info(PGconn *origin_conn)
 }
 
 /*
- * spock_create_slot_and_get_progress
+ * spock_create_slot_and_read_progress
  *
  * Pauses apply workers, creates a replication slot via the replication
  * protocol (which returns a snapshot consistent with the slot's WAL
@@ -568,7 +568,7 @@ adjust_progress_info(PGconn *origin_conn)
  * after the COPY phase completes.
  */
 static char *
-spock_create_slot_and_get_progress(PGconn *conn, PGconn *repl_conn,
+spock_create_slot_and_read_progress(PGconn *conn, PGconn *repl_conn,
 								   const char *slot_name,
 								   Oid origin_node_id, Oid subscriber_node_id,
 								   XLogRecPtr *lsn_out, List **progress_out)
@@ -670,7 +670,7 @@ spock_create_slot_and_get_progress(PGconn *conn, PGconn *repl_conn,
 
 	/* Read peer progress via the SQL function (slot already exists) */
 	appendStringInfo(&query,
-					 "SELECT * FROM spock.create_slot_with_progress"
+					 "SELECT * FROM spock.read_peer_progress"
 					 "('%s', %u, %u)",
 					 slot_name, origin_node_id, subscriber_node_id);
 	res = PQexec(conn, query.data);
@@ -682,7 +682,7 @@ spock_create_slot_and_get_progress(PGconn *conn, PGconn *repl_conn,
 
 	nrows = PQntuples(res);
 	if (nrows < 1)
-		elog(ERROR, "spock.create_slot_with_progress returned no rows");
+		elog(ERROR, "spock.read_peer_progress returned no rows");
 
 	/* Row 0 is the header row: lsn + snapshot, progress fields all NULL.
 	 * lsn_out and snapshot are already set from the replication protocol;
@@ -771,7 +771,7 @@ spock_create_slot_and_get_progress(PGconn *conn, PGconn *repl_conn,
  * spock_release_slot_snapshot
  *
  * Rolls back the snapshot transaction opened by
- * spock_create_slot_and_get_progress and closes the connection.
+ * spock_create_slot_and_read_progress and closes the connection.
  */
 static void
 spock_release_slot_snapshot(PGconn *conn)
@@ -1454,7 +1454,7 @@ spock_sync_subscription(SpockSubscription *sub)
 		 */
 		PG_TRY();
 		{
-			snapshot = spock_create_slot_and_get_progress(
+			snapshot = spock_create_slot_and_read_progress(
 									origin_conn,
 									origin_conn_repl,
 									sub->slot_name,