[CentOS] Re: centos] 4.4 upgrade problems)

[R P Herrold]

On Sat, 9 Sep 2006, Lamar Owen wrote:
> On Tuesday 05 September 2006 22:35, R P Herrold wrote:
>> This bug hinges, very much, on the non-atomic nature of 
>> 'hot' system updates, and the fact that the yum-needed, 
>> sqlite-maintianed cache of packages got munged half way 
>> through, to reproduce.

> Sounds like a database type issue; ... That is, a filesystem 
> on ACID.  (Atomicity, Consistency, Isolation, Durability: 
> the magic mantra of database management).

*flashback* Acid - Berkeley - BSD -- coincidence? I think 
_not_.  ;)

*cough* Nothing so complex needed here; a simple early flock 
holding upon the sqlite-python verson with which the cache was 
created would have sufficed, in thinking about the bugreport.

As to ACID, a interesting sidelight (as to MySQL, not the 
PostgreSQL which Lamar mentioned).  It turns out that even 
with use of the Innodb backend engine in MySQL as we ship it 
in CentOS, and as inherited from the upstream PNAELV, for 
perfomance reasons, full ACID compliance is turned off.  We 
found a reproducer in a project I am involved with, which 
forced us to dig down and at the database level, to ensure 
that full compliance is enabled from the initial connection on 
[http://www.trading-shim.org/capitals/?NEWS, July 30 release], 
to solve a need for transaction Isolation 
[http://dev.mysql.com/books/mysqlpress/mysql-tutorial/ch10.html].

As to using a database backend filesystem, with full ACID 
consistency enabled, I think a certain OS vendor in Redmond 
had to backaway from that featureset bulletpoint item in a 
somewhat delayed upcoming release.  One had better be willing 
to suffer performance hit collateral damage with the present 
state of the implementaion art. Think of inviting a gorilla 
over, to use an anvil to swat a fly in the kitchen.  ouch.

-- Russ Herrold