[Pdns-users] MySQL-Reconnecting with MySQL >5.0.3

[Norbert Sendetzky]

Hi Jason

> Why are you assigning this as a MySQL design flaw? We've designed
> quite a few InnoDB apps that handle just this situation very well in
> event of a rollback.

When your applications notice that the connection is lost, they also know that 
transactions where rolled back and they can either try to establish a new 
connection and redo the transaction or exit. Your applications know what has 
happend!

Contrary, if the MySQL client library does a reconnection silently, your 
applications don't know that the transactions were rolled back. They assume 
they are still in the middle of the transaction and keep going changing 
records. Unfortunately, the reestablished connection is set to the default 
state which means that no transaction is in progress and auto-commit is 
turned on. All changes will be permanent immediately and if you send a 
ROLLBACK statement to the database, nothing will happen. In case of a COMMIT, 
you've lost the changes up to the reconnect (which you haven't noticed).

This leads to errors which are almost impossible to detect and therefore I 
consider this feature a design flaw if it's enabled by default. It makes only 
sense if you are only reading from a database and don't use transactions or 
locks.


Norbert
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