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Re: (wtf) Top 20 Open Source Software Projects in the Enterprise

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: PostgreSQL Advocacy List <pgsql-advocacy(at)postgresql(dot)org>
Subject: Re: (wtf) Top 20 Open Source Software Projects in the Enterprise
Date: 2007-07-24 20:32:21
Message-ID: Pine.GSO.4.64.0707241629080.9785@westnet.com (view raw or flat)
Thread:
Lists: pgsql-advocacy
On Tue, 24 Jul 2007, Jonah H. Harris wrote:

> At this point in time, I don't believe you can use anything but MyISAM 
> for the catalog tables.  So, I imagine it would be possible to logically 
> corrupt a system if DDL was occurring at the exact point of a crash.

They work around this the old-fashioned MySQL way, with lots of locks.
See http://forge.mysql.com/wiki/MySQL_Internals_Data_and_meta-data_locking

For example, this is their ALTER TABLE internal workflow:  "
  * open and lock table with TL_WRITE_ALLOW_READ
  * create an altered copy of the table with a temporary name
  * force and wait until all instances of table are closed (lock 
upgrade!)
  * swap the new and old versions
  * drop the old version"

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD

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