From: Adrian Klaver <adrian.klaver@aklaver.com>
To: arnaud.listes@codata.eu, Bruce Momjian <bruce@momjian.us>
Cc: PG-General Mailing List <pgsql-general@postgresql.org>
Subject: Re: pg_upgrade --link on Windows
Date: Fri, 9 Jun 2017 07:55:55 -0700
Message-ID: <0405d125-929b-ab4a-b7be-d49c09e7c056@aklaver.com> (raw)
In-Reply-To: <a892509c-0eb4-42a4-1370-6cb0ac3bc1c3@codata.eu>
References: <8da3dbd9-7daf-5589-0cc8-0eede930a492@codata.eu>
<20170609140724.GB21215@momjian.us>
<a892509c-0eb4-42a4-1370-6cb0ac3bc1c3@codata.eu>
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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@aklaver.com
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To: pgsql-docs@postgresql.org
Cc: adrian.klaver@aklaver.com, bruce@momjian.us, pgsql-general@postgresql.org
Subject: Re: pg_upgrade --link on Windows
In-Reply-To: <0405d125-929b-ab4a-b7be-d49c09e7c056@aklaver.com>
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