Fix handling of missing files when using pg_rewind with online source

michaelpq · michaelpq · commit 92927477ff70 · 2020-07-15T15:17:36.000+09:00
When working with an online source cluster, pg_rewind gets a list of all the files in the source data directory using a WITH RECURSIVE query, returning a NULL result for a file's metadata if it gets removed between the moment it is listed in a directory and the moment its metadata is obtained with pg_stat_file() (say a recycled WAL segment). The query result was processed in such a way that for each tuple we checked only that the first file's metadata was NULL. This could have two consequences, both resulting in a failure of the rewind: - If the first tuple referred to a removed file, all files from the source would be ignored. - Any file actually missing would not be considered as such. While on it, rework slightly the code so as no values are saved if we know that a file is going to be skipped. Issue introduced by b36805f, so backpatch down to 9.5. Author: Justin Pryzby, Michael Paquier Reviewed-by: Daniel Gustafsson, Masahiko Sawada Discussion: https://postgr.es/m/20200713061010.GC23581@telsasoft.com Backpatch-through: 9.5
diff --git a/src/bin/pg_rewind/libpq_fetch.c b/src/bin/pg_rewind/libpq_fetch.c
@@ -216,13 +216,13 @@ libpqProcessFileList(void)
 	/* Read result to local variables */
 	for (i = 0; i < PQntuples(res); i++)
 	{
-		char	   *path = PQgetvalue(res, i, 0);
-		int64		filesize = atol(PQgetvalue(res, i, 1));
-		bool		isdir = (strcmp(PQgetvalue(res, i, 2), "t") == 0);
-		char	   *link_target = PQgetvalue(res, i, 3);
+		char	   *path;
+		int64		filesize;
+		bool		isdir;
+		char	   *link_target;
 		file_type_t type;
 
-		if (PQgetisnull(res, 0, 1))
+		if (PQgetisnull(res, i, 1))
 		{
 			/*
 			 * The file was removed from the server while the query was
@@ -231,6 +231,11 @@ libpqProcessFileList(void)
 			continue;
 		}
 
+		path = PQgetvalue(res, i, 0);
+		filesize = atol(PQgetvalue(res, i, 1));
+		isdir = (strcmp(PQgetvalue(res, i, 2), "t") == 0);
+		link_target = PQgetvalue(res, i, 3);
+
 		if (link_target[0])
 			type = FILE_TYPE_SYMLINK;
 		else if (isdir)
