pg_upgrade: Parallelize contrib/isn check.

This commit makes use of the new task framework in pg_upgrade to
parallelize the check for contrib/isn functions that rely on the
bigint data type.  This step will now process multiple databases
concurrently when pg_upgrade's --jobs option is provided a value
greater than 1.

Reviewed-by: Daniel Gustafsson, Ilya Gladyshev
Discussion: https://postgr.es/m/20240516211638.GA1688936%40nathanxps13

src/bin/pg_upgrade/check.c

@@ -1225,6 +1225,39 @@ check_for_prepared_transactions(ClusterInfo *cluster)
 	check_ok();
 }
 
+/*
+ * Callback function for processing result of query for
+ * check_for_isn_and_int8_passing_mismatch()'s UpgradeTask.  If the query
+ * returned any rows (i.e., the check failed), write the details to the report
+ * file.
+ */
+static void
+process_isn_and_int8_passing_mismatch(DbInfo *dbinfo, PGresult *res, void *arg)
+{
+	bool		db_used = false;
+	int			ntups = PQntuples(res);
+	int			i_nspname = PQfnumber(res, "nspname");
+	int			i_proname = PQfnumber(res, "proname");
+	UpgradeTaskReport *report = (UpgradeTaskReport *) arg;
+
+	AssertVariableIsOfType(&process_isn_and_int8_passing_mismatch,
+						   UpgradeTaskProcessCB);
+
+	for (int rowno = 0; rowno < ntups; rowno++)
+	{
+		if (report->file == NULL &&
+			(report->file = fopen_priv(report->path, "w")) == NULL)
+			pg_fatal("could not open file \"%s\": %m", report->path);
+		if (!db_used)
+		{
+			fprintf(report->file, "In database: %s\n", dbinfo->db_name);
+			db_used = true;
+		}
+		fprintf(report->file, "  %s.%s\n",
+				PQgetvalue(res, rowno, i_nspname),
+				PQgetvalue(res, rowno, i_proname));
+	}
+}
 
 /*
  *	check_for_isn_and_int8_passing_mismatch()
@@ -1236,9 +1269,13 @@ check_for_prepared_transactions(ClusterInfo *cluster)
 static void
 check_for_isn_and_int8_passing_mismatch(ClusterInfo *cluster)
 {
-	int			dbnum;
-	FILE	   *script = NULL;
-	char		output_path[MAXPGPATH];
+	UpgradeTask *task;
+	UpgradeTaskReport report;
+	const char *query = "SELECT n.nspname, p.proname "
+		"FROM   pg_catalog.pg_proc p, "
+		"       pg_catalog.pg_namespace n "
+		"WHERE  p.pronamespace = n.oid AND "
+		"       p.probin = '$libdir/isn'";
 
 	prep_status("Checking for contrib/isn with bigint-passing mismatch");
 
@@ -1250,54 +1287,20 @@ check_for_isn_and_int8_passing_mismatch(ClusterInfo *cluster)
 		return;
 	}
 
-	snprintf(output_path, sizeof(output_path), "%s/%s",
+	report.file = NULL;
+	snprintf(report.path, sizeof(report.path), "%s/%s",
 			 log_opts.basedir,
 			 "contrib_isn_and_int8_pass_by_value.txt");
 
-	for (dbnum = 0; dbnum < cluster->dbarr.ndbs; dbnum++)
-	{
-		PGresult   *res;
-		bool		db_used = false;
-		int			ntups;
-		int			rowno;
-		int			i_nspname,
-					i_proname;
-		DbInfo	   *active_db = &cluster->dbarr.dbs[dbnum];
-		PGconn	   *conn = connectToServer(cluster, active_db->db_name);
-
-		/* Find any functions coming from contrib/isn */
-		res = executeQueryOrDie(conn,
-								"SELECT n.nspname, p.proname "
-								"FROM	pg_catalog.pg_proc p, "
-								"		pg_catalog.pg_namespace n "
-								"WHERE	p.pronamespace = n.oid AND "
-								"		p.probin = '$libdir/isn'");
-
-		ntups = PQntuples(res);
-		i_nspname = PQfnumber(res, "nspname");
-		i_proname = PQfnumber(res, "proname");
-		for (rowno = 0; rowno < ntups; rowno++)
-		{
-			if (script == NULL && (script = fopen_priv(output_path, "w")) == NULL)
-				pg_fatal("could not open file \"%s\": %m", output_path);
-			if (!db_used)
-			{
-				fprintf(script, "In database: %s\n", active_db->db_name);
-				db_used = true;
-			}
-			fprintf(script, "  %s.%s\n",
-					PQgetvalue(res, rowno, i_nspname),
-					PQgetvalue(res, rowno, i_proname));
-		}
-
-		PQclear(res);
-
-		PQfinish(conn);
-	}
+	task = upgrade_task_create();
+	upgrade_task_add_step(task, query, process_isn_and_int8_passing_mismatch,
+						  true, &report);
+	upgrade_task_run(task, cluster);
+	upgrade_task_free(task);
 
-	if (script)
+	if (report.file)
 	{
-		fclose(script);
+		fclose(report.file);
 		pg_log(PG_REPORT, "fatal");
 		pg_fatal("Your installation contains \"contrib/isn\" functions which rely on the\n"
 				 "bigint data type.  Your old and new clusters pass bigint values\n"
@@ -1305,7 +1308,7 @@ check_for_isn_and_int8_passing_mismatch(ClusterInfo *cluster)
 				 "manually dump databases in the old cluster that use \"contrib/isn\"\n"
 				 "facilities, drop them, perform the upgrade, and then restore them.  A\n"
 				 "list of the problem functions is in the file:\n"
-				 "    %s", output_path);
+				 "    %s", report.path);
 	}
 	else
 		check_ok();