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commit    14fe8041395cdfaf05c736911080982d021c5e9d
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Wed Jul 15 06:17:55 2020 +0000
First released in: 14.0, 9.5.23, 9.6.19, 10.14, 11.9, 12.4, 13.0

    Fix handling of missing files when using pg_rewind with online source
    
    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


 src/bin/pg_rewind/libpq_fetch.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/bin/pg_rewind/libpq_fetch.c b/src/bin/pg_rewind/libpq_fetch.c
index 101161c46ef..f599811411b 100644
--- a/src/bin/pg_rewind/libpq_fetch.c
+++ b/src/bin/pg_rewind/libpq_fetch.c
@@ -221,13 +221,13 @@ 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
@@ -236,6 +236,11 @@ 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)


[parent: c732df133a3d]