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Fix handling of missing files when using pg_rewind with online source

author Michael Paquier <michael@paquier.xyz>

2020年7月15日 06:17:36 +0000 (15:17 +0900)

committer Michael Paquier <michael@paquier.xyz>

2020年7月15日 06:17:36 +0000 (15:17 +0900)

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 patch | blob | blame | history

diff --git a/src/bin/pg_rewind/libpq_fetch.c b/src/bin/pg_rewind/libpq_fetch.c

index 2c1a86943140ec216d5ab08ed05b239bbc2349a7..0dae75b86287c9318197003690c44eafbb9c2bea 100644 (file)

--- 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)

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