Re: pgsql: Map basebackup tablespaces using a tablespace_map file
| От | Amit Kapila |
|---|---|
| Тема | Re: pgsql: Map basebackup tablespaces using a tablespace_map file |
| Дата | |
| Msg-id | CAA4eK1JuSn29N6SSrk19yoR160KrdObzgyLXyqH2QSGC+wdoRQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: pgsql: Map basebackup tablespaces using a tablespace_map file (Andrew Dunstan <andrew@dunslane.net>) |
| Список | pgsql-committers |
On Tue, May 12, 2015 at 9:02 PM, Andrew Dunstan <andrew@dunslane.net> wrote:
On 05/12/2015 10:33 AM, Heikki Linnakangas wrote:On 05/12/2015 04:42 PM, Andrew Dunstan wrote:+
+ /*
+ * Remove the existing symlink if any and Create the symlink
+ * under PGDATA. We need to use rmtree instead of rmdir as
+ * the link location might contain directories or files
+ * corresponding to the actual path. Some tar utilities do
+ * things that way while extracting symlinks.
+ */
+ if (lstat(linkloc, &st) == 0 && S_ISDIR(st.st_mode))
+ {
+ if (!rmtree(linkloc,true))
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not remove directory \"%s\": %m",
+ linkloc)));
+ }
+ else
+ {
+ if (unlink(linkloc) < 0 && errno != ENOENT)
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not remove symbolic link \"%s\": %m",
+ linkloc)));
+ }
+
That's scary. What tar utilitiy replaces the symlink with a non-empty directory?
IIRC, it was star utility by using --copysymlinks options.
It will actually copy the symlink data at appropriate location,
but will not maintain symlink after extraction.
I don't have a link handly for it, but can again search for
it and send you if you want to have a look.
What if you call pg_start_backup() and take the backup with a utility that follows symlinks? I wouldn't recommend using such a tool, but with this patch, it will zap all the tablespaces. Before this, you at least got a working database and could read out all the data or fix the symlinks afterwards.
Yeah, but I don't think user will do such a thing without
being aware of the same and if he is aware, he will either
restore the symlinks before starting the server or would
atleast keep a copy of such a backup until he is able to
restore the database completely.
Do you think adding a note in docs makes sense?
Why is the RelationCacheInitFileRemove() call moved?
I will let Amit comment on this.
Because it assumes that tablespace directory pg_tblspc is all in
place and it tries to remove the files by reading pg_tblspc
directory as well. Now as we setup the symlinks in pg_tblspc
after reading tablespace_map file, so we should remove relcache init
file once the symlinks are setup in pg_tblspc directory.
XLogRecPtr
do_pg_start_backup(const char *backupidstr, bool fast, TimeLineID *starttli_p,
- char **labelfile)
+ char **labelfile, DIR *tblspcdir, List **tablespaces,
+ char **tblspcmapfile, bool infotbssize,
+ bool needtblspcmapfile)
Why does this need to take tblspcdir as argument?
It needs to be called from perform_base_backup() which already
has access to tblspcdir.
Wouldn't it make more sense to open the directory inside do_pg_start_backup?
Good point. It does look cleaner to do that.
If you prefer that way, I can look into rearranging the
code.
In the BASE_BACKUP command, is there any reason to not always include the tablespace map?
The main reason is that it is not required to restore symlinks
for plain format. Also I think it can cause a problem if user
has used --tablespace-mapping option in plain format as the
tablespace_map file doesn't contain information for same and recovery
will try to restore symlinks for wrong path based on tablespace_map
file.
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