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Fix handling of missing files when using pg_rewind with online source

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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
This commit is contained in:
Michael Paquier 2020-07-15 15:17:49 +09:00
parent 4e02f88a4e
commit 23924feca0
1 changed files with 10 additions and 5 deletions
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15
src/bin/pg_rewind/libpq_fetch.c
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@ -220,13 +220,13 @@ libpqProcessFileList(void)
/* Read result to local variables */ /* Read result to local variables */
for (i = 0; i < PQntuples(res); i++) for (i = 0; i < PQntuples(res); i++)
{ {
char *path = PQgetvalue(res, i, 0); char *path;
int64 filesize = atol(PQgetvalue(res, i, 1)); int64 filesize;
bool isdir = (strcmp(PQgetvalue(res, i, 2), "t") == 0); bool isdir;
char *link_target = PQgetvalue(res, i, 3); char *link_target;
file_type_t type; 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 * The file was removed from the server while the query was
@ -235,6 +235,11 @@ libpqProcessFileList(void)
continue; 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]) if (link_target[0])
type = FILE_TYPE_SYMLINK; type = FILE_TYPE_SYMLINK;
else if (isdir) else if (isdir)