From: Bruce Momjian <bruce@momjian.us>
To: Adrian Klaver <adrian.klaver@aklaver.com>
Cc: arnaud.listes@codata.eu, PG-General Mailing List <pgsql-general@postgresql.org>
Cc: PostgreSQL-documentation <pgsql-docs@postgresql.org>
Subject: Re: [GENERAL] pg_upgrade --link on Windows
Date: Tue, 13 Jun 2017 16:07:48 -0400
Message-ID: <20170613200748.GB13879@momjian.us> (raw)
In-Reply-To: <0405d125-929b-ab4a-b7be-d49c09e7c056@aklaver.com>
References: <8da3dbd9-7daf-5589-0cc8-0eede930a492@codata.eu>
<20170609140724.GB21215@momjian.us>
<a892509c-0eb4-42a4-1370-6cb0ac3bc1c3@codata.eu>
<0405d125-929b-ab4a-b7be-d49c09e7c056@aklaver.com>
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On Fri, Jun 9, 2017 at 07:55:55AM -0700, Adrian Klaver wrote:
> On 06/09/2017 07:39 AM, Arnaud L. wrote:
> >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
[docs list added]
I apologize for not being smarter on this thread. When I helped with
the Windows port, I was told Windows didn't have hard links for use by
tablespace directories, so I got it into my head that Windows didn't
have hard links. Therefore, when I was writing the docs, I called them
junction points.
Looking back to Postgres 9.0 where pg_upgrade was added to the tree, I
see that the code even at that time used hard links on Windows. I have
created the attached patch which I will apply to all current Postgres
versions to fix this error.
Thanks for the report and the research. :-)
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
--
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http://www.postgresql.org/mailpref/pgsql-docsAttachments:junction.diff (text/x-diff, 767B) downloaddiff --git a/doc/src/sgml/ref/pgupgrade.sgml b/doc/src/sgml/ref/pgupgrade.sgmlnew file mode 100644index bf58a0a..4e27112
*** a/doc/src/sgml/ref/pgupgrade.sgml
--- b/doc/src/sgml/ref/pgupgrade.sgml
***************
*** 123,129 ****
<term><option>-k</option></term>
<term><option>--link</option></term>
<listitem><para>use hard links instead of copying files to the new
! cluster (use junction points on Windows)</para></listitem>
</varlistentry>
<varlistentry>
--- 123,129 ----
<term><option>-k</option></term>
<term><option>--link</option></term>
<listitem><para>use hard links instead of copying files to the new
! cluster</para></listitem>
</varlistentry>
<varlistentry>
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To: pgsql-docs@postgresql.org
Cc: bruce@momjian.us, adrian.klaver@aklaver.com, pgsql-general@postgresql.org
Subject: Re: [GENERAL] pg_upgrade --link on Windows
In-Reply-To: <20170613200748.GB13879@momjian.us>
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