Thread: pgsql: Map basebackup tablespaces using a tablespace_map file
Map basebackup tablespaces using a tablespace_map file Windows can't reliably restore symbolic links from a tar format, so instead during backup start we create a tablespace_map file, which is used by the restoring postgres to create the correct links in pg_tblspc. The backup protocol also now has an option to request this file to be included in the backup stream, and this is used by pg_basebackup when operating in tar mode. This is done on all platforms, not just Windows. This means that pg_basebackup will not not work in tar mode against 9.4 and older servers, as this protocol option isn't implemented there. Amit Kapila, reviewed by Dilip Kumar, with a little editing from me. Branch ------ master Details ------- http://git.postgresql.org/pg/commitdiff/72d422a5227ef6f76f412486a395aba9f53bf3f0 Modified Files -------------- doc/src/sgml/backup.sgml | 32 +-- doc/src/sgml/func.sgml | 14 +- doc/src/sgml/protocol.sgml | 15 +- doc/src/sgml/ref/pg_basebackup.sgml | 14 +- src/backend/access/transam/xlog.c | 387 ++++++++++++++++++++++++++++++-- src/backend/access/transam/xlogfuncs.c | 12 +- src/backend/replication/basebackup.c | 138 +++++------- src/backend/replication/repl_gram.y | 16 +- src/backend/replication/repl_scanner.l | 1 + src/bin/pg_basebackup/pg_basebackup.c | 5 +- src/include/access/xlog.h | 9 +- src/include/replication/basebackup.h | 10 + 12 files changed, 519 insertions(+), 134 deletions(-)
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? 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. Why is the RelationCacheInitFileRemove() call moved? > 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? Wouldn't it make more sense to open the directory inside do_pg_start_backup? In the BASE_BACKUP command, is there any reason to not always include the tablespace map? IOW, do we really need the TABLESPACE_MAP option? - Heikki
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? > > 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. > > Why is the RelationCacheInitFileRemove() call moved? I will let Amit comment on this. > >> 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? Wouldn't it make > more sense to open the directory inside do_pg_start_backup? Good point. It does look cleaner to do that. > > In the BASE_BACKUP command, is there any reason to not always include > the tablespace map? IOW, do we really need the TABLESPACE_MAP option? > > > I assume it was done for minimal disturbance, i.e. that's where we need it. Amit, comments? cheers andrew
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.