From: Craig Vincent
Date: March 1 2000 3:54pm
Subject: True redundancy with MySQL
List-Archive: http://lists.mysql.com/mysql/29628
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I know this question gets asked often, however the archives on the MySQL =
site seem outdated and I couldn't find any solutions there.

I'm trying to come up with a solution for true redundancy on MySQL and =
so far have not come up with anything that isn't a disaster waiting to =
happen. Here were some potential theories:

Assume there are two databases (A and B) and updates/inserts are done =
via a CGI script.

Theory 1:

Database A receives all updates from CGI.  Every 5 minutes or so FTP =
Database A and overwrite Database B.  If Database A goes down CGI then =
sends all information to Database B =20

Potential problems with this:  Information updated since last A->B =
transfer will be lost.  Perhaps doing some log parsing can retain the =
information...but this would require more than likely manual activation =
of a data retrieval script.  B would also need to be copied back to A =
before CGI script realizes that DB A is back online...in a nutshell it =
requires precise timing, has potential race conditional and overall not =
fully automated

Theory 2:

CGI updates both Database A & B.  During retrieval programs can access =
either server for the information.

Potential problems:

First off this will slow down the CGI and increase server load as it =
requires two connections & queries not just one. Also if one database =
goes down something needs to be done to get the database that went down =
up to speed.  Can do parsing via log files but if times on servers are =
not exact there could be duplicated or lost data.

So right now neither solution is appealing to me :(  If someone has a =
working solution or can provide feedback on how I could improve either =
of the above theories please tell me.  I'm open to all ideas and =
suggestions.  Also rumour has it Linux was in the process of developing =
some sort of MySQL redundancy software...does anyone know if there's any =
truth to this?


Sincerely,

Craig Vincent


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