Don't choke on files that are removed while pg_rewind runs.

If a file is removed from the source server, while pg_rewind is running, the
invocation of pg_read_binary_file() will fail. Use the just-added missing_ok
option to that function, to have it return NULL instead, and handle that
gracefully. And similarly for pg_ls_dir and pg_stat_file.

Reported by Fujii Masao, fix by Michael Paquier.

diff --git a/src/bin/pg_rewind/libpq_fetch.c b/src/bin/pg_rewind/libpq_fetch.c
index 37e515bc98476a0b21b5550725b636fb5bca733b..05aa133cf36eaa527f0a331ba9e2ec0d145530c8 100644 (file)
--- a/src/bin/pg_rewind/libpq_fetch.c
+++ b/src/bin/pg_rewind/libpq_fetch.c
@@ -149,14 +149,14 @@ libpqProcessFileList(void)
    sql =
        "WITH RECURSIVE files (path, filename, size, isdir) AS (\n"
        "  SELECT '' AS path, filename, size, isdir FROM\n"
-       "  (SELECT pg_ls_dir('.') AS filename) AS fn,\n"
-       "        pg_stat_file(fn.filename) AS this\n"
+       "  (SELECT pg_ls_dir('.', true, false) AS filename) AS fn,\n"
+       "        pg_stat_file(fn.filename, true) AS this\n"
        "  UNION ALL\n"
        "  SELECT parent.path || parent.filename || '/' AS path,\n"
        "         fn, this.size, this.isdir\n"
        "  FROM files AS parent,\n"
-       "       pg_ls_dir(parent.path || parent.filename) AS fn,\n"
-       "       pg_stat_file(parent.path || parent.filename || '/' || fn) AS this\n"
+       "       pg_ls_dir(parent.path || parent.filename, true, false) AS fn,\n"
+       "       pg_stat_file(parent.path || parent.filename || '/' || fn, true) AS this\n"
        "       WHERE parent.isdir = 't'\n"
        ")\n"
        "SELECT path || filename, size, isdir,\n"
@@ -183,6 +183,15 @@ libpqProcessFileList(void)
        char       *link_target = PQgetvalue(res, i, 3);
        file_type_t type;
 
+       if (PQgetisnull(res, 0, 1))
+       {
+           /*
+            * The file was removed from the server while the query was
+            * running. Ignore it.
+            */
+           continue;
+       }
+
        if (link_target[0])
            type = FILE_TYPE_SYMLINK;
        else if (isdir)
@@ -259,8 +268,7 @@ receiveFileChunks(const char *sql)
        }
 
        if (PQgetisnull(res, 0, 0) ||
-           PQgetisnull(res, 0, 1) ||
-           PQgetisnull(res, 0, 2))
+           PQgetisnull(res, 0, 1))
        {
            pg_fatal("unexpected null values in result while fetching remote files\n");
        }
@@ -280,6 +288,21 @@ receiveFileChunks(const char *sql)
 
        chunk = PQgetvalue(res, 0, 2);
 
+       /*
+        * It's possible that the file was deleted on remote side after we
+        * created the file map. In this case simply ignore it, as if it was
+        * not there in the first place, and move on.
+        */
+       if (PQgetisnull(res, 0, 2))
+       {
+           pg_log(PG_DEBUG,
+                  "received NULL chunk for file \"%s\", file has been deleted\n",
+                  filename);
+           pg_free(filename);
+           PQclear(res);
+           continue;
+       }
+
        pg_log(PG_DEBUG, "received chunk for file \"%s\", offset %d, size %d\n",
               filename, chunkoff, chunksize);
 
@@ -445,7 +468,7 @@ libpq_executeFileMap(filemap_t *map)
     */
    sql =
        "SELECT path, begin, \n"
-       "  pg_read_binary_file(path, begin, len) AS chunk\n"
+       "  pg_read_binary_file(path, begin, len, true) AS chunk\n"
        "FROM fetchchunks\n";
 
    receiveFileChunks(sql);