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Re: BUG #6411: Backend process' crash when a foreign table is used in a dependent subquery on select clause

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: emre(dot)hasegeli(at)tart(dot)com(dot)tr
Cc: pgsql-bugs(at)postgresql(dot)org, Dave Page <dpage(at)pgadmin(dot)org>
Subject: Re: BUG #6411: Backend process' crash when a foreign table is used in a dependent subquery on select clause
Date: 2012-01-26 21:14:53
Message-ID: 4F21C24D.6070003@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-bugs
On 26.01.2012 14:46, emre(dot)hasegeli(at)tart(dot)com(dot)tr wrote:
> The following bug has been logged on the website:
>
> Bug reference:      6411
> Logged by:          Using a Foreign Table in a Dependent Subquery
> Email address:      emre(dot)hasegeli(at)tart(dot)com(dot)tr
> PostgreSQL version: 9.1.2
> Operating system:   Linux 3.0.0-14-generic #23-Ubuntu SMP Mon Nov 21 2
> Description:
>
> I installed Dave Page's MySQL Foreign Data Wrapper on GitHub [1]. It works
> fine until foreign table is used in a dependent subquery on select clause.

This mailing list is really for bugs in PostgreSQL itself, but I'll give 
this a shot...

> How to reproduce:
>
> Create extension mysql_fdw;
>
> Create server AMySQLServer
>      foreign data wrapper mysql_fdw
>      options (address '***', port '3306');
>
> Create user mapping for public
>      server AMySQLServer
>      options (username '***', password '***');
>
> Create foreign table AForeignTable (id integer) server AMySQLServer options
> (query 'Select id from ASchema.ATable');
>
> Select id, (select true from AForeignTable where AForeignTable.id =
> ATable.id) from ATable;
>
> WARNING:  57P02: terminating connection because of crash of another server
> process
> DETAIL:  The postmaster has commanded this server process to roll back the
> current transaction and exit, because another server process exited
> abnormally and possibly corrupted shared memory.
> HINT:  In a moment you should be able to reconnect to the database and
> repeat your command.
>
> [1] https://github.com/dpage/mysql_fdw

I'm guessing that there's mysql_fdw's rescan function isn't working 
correctly. Looking at the source, it seems to be calling 
"mysql_row_seek(festate->result, 0);". But according to MySQL's docs 
[1], that 2nd argument should be an opaque value returned by 
mysql_row_tell() or mysql_row_seek(), not a row number. I think 
mysql_data_seek should be used there instead of mysql_row_seek().

That said, I have no idea if that's causing the crash.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com

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