reindexdb: Fix the index-level REINDEX with multiple jobs

47f99a4 introduced a parallel index-level REINDEX.  The code was written
assuming that running run_reindex_command() with 'async == true' can schedule
a number of queries for a connection.  That's not true, and the second query
sent using run_reindex_command() will wait for the completion of the previous
one.

This commit fixes that by putting REINDEX commands for the same table into a
single query.

Also, this commit removes the 'async' argument from run_reindex_command(),
as only its call always passes 'async == true'.

Reported-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/202503071820.j25zn3lo4hvn%40alvherre.pgsql
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Backpatch-through: 17

Author: akorotkov

src/bin/scripts/reindexdb.c

@@ -50,10 +50,13 @@ static void reindex_all_databases(ConnParams *cparams,
 								  bool syscatalog, SimpleStringList *schemas,
 								  SimpleStringList *tables,
 								  SimpleStringList *indexes);
-static void run_reindex_command(PGconn *conn, ReindexType type,
+static void gen_reindex_command(PGconn *conn, ReindexType type,
 								const char *name, bool echo, bool verbose,
-								bool concurrently, bool async,
-								const char *tablespace);
+								bool concurrently, const char *tablespace,
+								PQExpBufferData *sql);
+static void run_reindex_command(PGconn *conn, ReindexType type,
+								const char *name, bool echo,
+								PQExpBufferData *sq);
 
 static void help(const char *progname);
 
@@ -285,7 +288,6 @@ reindex_one_database(ConnParams *cparams, ReindexType type,
 	ParallelSlotArray *sa;
 	bool		failed = false;
 	int			items_count = 0;
-	char	   *prev_index_table_name = NULL;
 	ParallelSlot *free_slot = NULL;
 
 	conn = connectDatabase(cparams, progname, echo, false, true);
@@ -421,44 +423,54 @@ reindex_one_database(ConnParams *cparams, ReindexType type,
 	cell = process_list->head;
 	do
 	{
+		PQExpBufferData sql;
 		const char *objname = cell->val;
-		bool		need_new_slot = true;
 
 		if (CancelRequested)
 		{
 			failed = true;
 			goto finish;
 		}
 
-		/*
-		 * For parallel index-level REINDEX, the indices of the same table are
-		 * ordered together and they are to be processed by the same job.  So,
-		 * we don't switch the job as soon as the index belongs to the same
-		 * table as the previous one.
-		 */
-		if (parallel && process_type == REINDEX_INDEX)
+		free_slot = ParallelSlotsGetIdle(sa, NULL);
+		if (!free_slot)
 		{
-			if (prev_index_table_name != NULL &&
-				strcmp(prev_index_table_name, indices_tables_cell->val) == 0)
-				need_new_slot = false;
-			prev_index_table_name = indices_tables_cell->val;
-			indices_tables_cell = indices_tables_cell->next;
+			failed = true;
+			goto finish;
 		}
 
-		if (need_new_slot)
+		ParallelSlotSetHandler(free_slot, TableCommandResultHandler, NULL);
+		initPQExpBuffer(&sql);
+		if (parallel && process_type == REINDEX_INDEX)
 		{
-			free_slot = ParallelSlotsGetIdle(sa, NULL);
-			if (!free_slot)
+			/*
+			 * For parallel index-level REINDEX, the indices of the same table
+			 * are ordered together and they are to be processed by the same
+			 * job.  So, we put all the relevant REINDEX commands into the
+			 * same SQL query to be processed by this job at once.
+			 */
+			gen_reindex_command(free_slot->connection, process_type, objname,
+								echo, verbose, concurrently, tablespace, &sql);
+			while (indices_tables_cell->next &&
+				   strcmp(indices_tables_cell->val, indices_tables_cell->next->val) == 0)
 			{
-				failed = true;
-				goto finish;
+				indices_tables_cell = indices_tables_cell->next;
+				cell = cell->next;
+				objname = cell->val;
+				appendPQExpBufferChar(&sql, '\n');
+				gen_reindex_command(free_slot->connection, process_type, objname,
+									echo, verbose, concurrently, tablespace, &sql);
 			}
-
-			ParallelSlotSetHandler(free_slot, TableCommandResultHandler, NULL);
+			indices_tables_cell = indices_tables_cell->next;
+		}
+		else
+		{
+			gen_reindex_command(free_slot->connection, process_type, objname,
+								echo, verbose, concurrently, tablespace, &sql);
 		}
-
 		run_reindex_command(free_slot->connection, process_type, objname,
-							echo, verbose, concurrently, true, tablespace);
+							echo, &sql);
+		termPQExpBuffer(&sql);
 
 		cell = cell->next;
 	} while (cell != NULL);
@@ -486,57 +498,57 @@ reindex_one_database(ConnParams *cparams, ReindexType type,
 		exit(1);
 }
 
+/*
+ * Append a SQL command required to reindex a given database object to the
+ * '*sql' string.
+ */
 static void
-run_reindex_command(PGconn *conn, ReindexType type, const char *name,
-					bool echo, bool verbose, bool concurrently, bool async,
-					const char *tablespace)
+gen_reindex_command(PGconn *conn, ReindexType type, const char *name,
+					bool echo, bool verbose, bool concurrently,
+					const char *tablespace, PQExpBufferData *sql)
 {
 	const char *paren = "(";
 	const char *comma = ", ";
 	const char *sep = paren;
-	PQExpBufferData sql;
-	bool		status;
 
 	Assert(name);
 
 	/* build the REINDEX query */
-	initPQExpBuffer(&sql);
-
-	appendPQExpBufferStr(&sql, "REINDEX ");
+	appendPQExpBufferStr(sql, "REINDEX ");
 
 	if (verbose)
 	{
-		appendPQExpBuffer(&sql, "%sVERBOSE", sep);
+		appendPQExpBuffer(sql, "%sVERBOSE", sep);
 		sep = comma;
 	}
 
 	if (tablespace)
 	{
-		appendPQExpBuffer(&sql, "%sTABLESPACE %s", sep,
+		appendPQExpBuffer(sql, "%sTABLESPACE %s", sep,
 						  fmtIdEnc(tablespace, PQclientEncoding(conn)));
 		sep = comma;
 	}
 
 	if (sep != paren)
-		appendPQExpBufferStr(&sql, ") ");
+		appendPQExpBufferStr(sql, ") ");
 
 	/* object type */
 	switch (type)
 	{
 		case REINDEX_DATABASE:
-			appendPQExpBufferStr(&sql, "DATABASE ");
+			appendPQExpBufferStr(sql, "DATABASE ");
 			break;
 		case REINDEX_INDEX:
-			appendPQExpBufferStr(&sql, "INDEX ");
+			appendPQExpBufferStr(sql, "INDEX ");
 			break;
 		case REINDEX_SCHEMA:
-			appendPQExpBufferStr(&sql, "SCHEMA ");
+			appendPQExpBufferStr(sql, "SCHEMA ");
 			break;
 		case REINDEX_SYSTEM:
-			appendPQExpBufferStr(&sql, "SYSTEM ");
+			appendPQExpBufferStr(sql, "SYSTEM ");
 			break;
 		case REINDEX_TABLE:
-			appendPQExpBufferStr(&sql, "TABLE ");
+			appendPQExpBufferStr(sql, "TABLE ");
 			break;
 	}
 
@@ -546,37 +558,43 @@ run_reindex_command(PGconn *conn, ReindexType type, const char *name,
 	 * object type.
 	 */
 	if (concurrently)
-		appendPQExpBufferStr(&sql, "CONCURRENTLY ");
+		appendPQExpBufferStr(sql, "CONCURRENTLY ");
 
 	/* object name */
 	switch (type)
 	{
 		case REINDEX_DATABASE:
 		case REINDEX_SYSTEM:
-			appendPQExpBufferStr(&sql,
+			appendPQExpBufferStr(sql,
 								 fmtIdEnc(name, PQclientEncoding(conn)));
 			break;
 		case REINDEX_INDEX:
 		case REINDEX_TABLE:
-			appendQualifiedRelation(&sql, name, conn, echo);
+			appendQualifiedRelation(sql, name, conn, echo);
 			break;
 		case REINDEX_SCHEMA:
-			appendPQExpBufferStr(&sql, name);
+			appendPQExpBufferStr(sql, name);
 			break;
 	}
 
 	/* finish the query */
-	appendPQExpBufferChar(&sql, ';');
+	appendPQExpBufferChar(sql, ';');
+}
 
-	if (async)
-	{
-		if (echo)
-			printf("%s\n", sql.data);
+/*
+ * Run one or more reindex commands accumulated in the '*sql' string against
+ * a given database connection.
+ */
+static void
+run_reindex_command(PGconn *conn, ReindexType type, const char *name,
+					bool echo, PQExpBufferData *sql)
+{
+	bool		status;
 
-		status = PQsendQuery(conn, sql.data) == 1;
-	}
-	else
-		status = executeMaintenanceCommand(conn, sql.data, echo);
+	if (echo)
+		printf("%s\n", sql->data);
+
+	status = PQsendQuery(conn, sql->data) == 1;
 
 	if (!status)
 	{
@@ -603,14 +621,7 @@ run_reindex_command(PGconn *conn, ReindexType type, const char *name,
 							 name, PQdb(conn), PQerrorMessage(conn));
 				break;
 		}
-		if (!async)
-		{
-			PQfinish(conn);
-			exit(1);
-		}
 	}
-
-	termPQExpBuffer(&sql);
 }
 
 /*