Subject: Re: [GENERAL] Column rename in an extension update script
To: Philippe BEAUDOIN <phb.emaj@free.fr>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
References: <2cf7941e-4e41-7714-3de8-37b1a8f74dff@free.fr>
From: Julien Rouhaud <julien.rouhaud@dalibo.com>
Message-ID: <24fbcf75-04d2-9d10-ac12-c99fe4ca96a4@dalibo.com>
Date: Tue, 2 May 2017 21:45:26 +0200
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moving this thread to -hackers, since this looks like a bug.

On 01/05/2017 08:54, Philippe BEAUDOIN wrote:
> Hi all,
> 
> I am coding an update script for an extension. And I am in trouble when
> trying to rename a column of an existing table.
> 
> Just after the ALTER TABLE statement, I want to access this table. But
> at this time, the altered column is not visible with its new name.
> 

I can reproduce this issue.

It looks like this is due to missing cache invalidation between the
ALTER TABLE execution and next query planning (failure happens during
pg_analyze_and_rewrite()).

AFAICT, CommandCounterIncrement() is responsible for handling
invalidation messages, but in execute_sql_string() this function is
called before executing a Stmt instead of after.  Moving the
CommandCounterIncrement() just before the PopActiveSnapshot() call (and
removing the final one) fixes this issue for me, but I have no idea if
this is the right fix.

-- 
Julien Rouhaud
http://dalibo.com - http://dalibo.org


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