On 06/09/2017 07:39 AM, Arnaud L. wrote:
Le 9/06/2017 à 16:07, Bruce Momjian a écrit :
I was told junction points on Windows were hard links and no one has
ever complained about not being able to remove them.
Sorry, I think my explanation was not very clear.
You can remove the link, but the point is to remove the target (i.e. the
old-data-dir).
You can do this with a hard link (there still exists a hardlink pointing
to the inode so it remains), but with a soft link you end up with a link
to nothing.
Deleting a junction target in Windows will work, but you'll have an
error trying to access the junction directory (directory not found).
See this page for more details :
http://cects.com/overview-to-understanding-hard-links-junction-points-and-symbolic-links-in-windows/
Under "Hard Link (Linking for individual files)" :
"If the target is deleted, its content is still available through the
hard link"
Junction Point (Directory Hard Link):
"If the target is moved, renamed or deleted, the Junction Point still
exists, but points to a non-existing directory"
BUT, when I try to "pg_upgrade --link --check" with old-data-dir and
new-data-dir on different volumes, I get an error saying that both
directories must be on the same volume if --link is used.
So maybe pg_upgrade uses hard-links (i.e. to files), and only the
documentation is wrong by calling them junctions (i.e. soft links to
files) ?
Looks that way. In file.c in ~/src/bin/pg_upgrade I see:
#ifdef WIN32
300 /* implementation of pg_link_file() on Windows */
301 static int
302 win32_pghardlink(const char *src, const char *dst)
303 {
304 /*
305 * CreateHardLinkA returns zero for failure
306 * http://msdn.microsoft.com/en-us/library/aa363860(VS.85).aspx
307 */
308 if (CreateHardLinkA(dst, src, NULL) == 0)
309 {
310 _dosmaperr(GetLastError());
311 return -1;
312 }
313 else
314 return 0;
315 }
316 #endif
Regards
--
Arnaud
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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