Re: (wtf) Top 20 Open Source Software Projects in the Enterprise - Mailing list 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@gregsmith.com http://www.gregsmith.com Baltimore, MD