Date: Thu, 29 Jul 2021 13:43:09 -0400
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Bruce Momjian <bruce@momjian.us>
Cc: Dave Cramer <davecramer@gmail.com>,
	"David G. Johnston" <david.g.johnston@gmail.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: pg_upgrade does not upgrade pg_stat_statements properly
Message-ID: <202107291743.pqlj3s2uilfu@alvherre.pgsql>
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On 2021-Jul-29, Bruce Momjian wrote:

> +     If the old cluster used extensions, whether from
> +     <filename>contrib</filename> or some other source, it used
> +     shared object files (or DLLs) to implement these extensions, e.g.,
> +     <filename>pgcrypto.so</filename>.  Now, shared object files matching
> +     the new server binary must be installed in the new cluster, usually
> +     via operating system commands.  Do not load the schema definitions,
> +     e.g., <command>CREATE EXTENSION pgcrypto</command>, because these
> +     will be copied from the old cluster.  (Extensions should be upgraded
> +     later using <literal>ALTER EXTENSION ... UPGRADE</literal>.)

I propose this:

<para>
  If the old cluster used shared-object files (or DLLs) for extensions
  or other loadable modules, install recompiled versions of those files
  onto the new cluster.
  Do not install the extension themselves (i.e., do not run
  <command>CREATE EXTENSION</command>), because extension definitions
  will be carried forward from the old cluster.
</para>

<para>
  Extensions can be upgraded after pg_upgrade completes using
  <command>ALTER EXTENSION ... UPGRADE</command>, on a per-database
  basis.
</para>

I suggest " ... for extensions or other loadable modules" because
loadable modules aren't necessarily for extensions.  Also, it's
perfectly possible to have extension that don't have a loadable module.

I suggest "extension definitions ... carried forward" instead of
"extensions ... copied" (your proposed text) to avoid the idea that
files are copied; use it instead of "schema definitions ... upgraded"
(the current docs) to avoid the idea that they are actually upgraded;
also, "schema definition" seems a misleading term to use here.

I suggest "can be upgraded" rather than "should be upgraded" because
we're not making a recommendation, merely stating the fact that it is
possible to do so.

I suggest using the imperative mood, to be consistent with the
surrounding text.  (Applies to the first para; the second para is
informative.)


I haven't seen it mentioned in the thread, but I think the final phrase
of this <step> should be a separate step,

<step>
 <title>Copy custom full-text search files</title>
 <para>
  Copy any custom full text search file (dictionary, synonym, thesaurus,
  stop word list) to the new server.
 </para>
</step>

While this is closely related to extensions, it's completely different.

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/
"Sallah, I said NO camels! That's FIVE camels; can't you count?"
(Indiana Jones)