[Koha] MySQL and foreign keys

[paul POULAIN]

Williams, Olwen - SAL a écrit:

>I'm not about to argue one database over another. I've worked a lot in
>databases that don't enforce integrity, and you need to include the
>integrity in your code.  This is sometimes easier said than done.  We began
>using Postgres at the very start of Koha, but found problems making some
>queries run efficiently.  MySQL ran them so we changed.  I don't know to
>what extent the problem were in my lack of experience and how much was the
>fault of Postgres, and how much the two database have changed in the
>meantime.
>

>Last night I attended a PerlMongers group meeting here in Oakland, CA
>and one of the presenters at the meeting asserted that MySQL could not
>claim to be a completely relational database because it doesn't let you
>define foreign keys.  As a result, he feels that MySQL fails the ACID
>test (atomicity, consistency, referential integrity, and durability),
>and he advised people to avoid using it in Perl applications and instead
>use Postgres or some other relational database with more stability.  He
>cited an example where you might have a one-to-one relationship between
>primary key values in two tables and if you deleted a value from one of
>the tables, MySQL would leave that value in the other table as dangling
>data without warning you to take care of it and as a result really mess
>up your database.
>
>Can anyone on the Koha list comment on this assertion and what the
>consequences might be for Koha?
>
You're all of you completly right : mySQL 3 completly fails to be an 
ACID database. In fact, some person (like me), thinks and say mySQL 
should'nt be called "relational database", but "indexed file manager". 
But most people don't like to hear that :-)

The consequence is that koha must handle the code to insure the 
consistency and the referential integrity.

There are other problems with mySQL : it does not handle transactions, 
nor stored procedures, and many more things.
If we had to rewrite koha, maybe i would propose either Postgres or 
Interbase/Firebird, which are true ACID db.

Note however, that mySQL is better (faster) on "Write Sometimes Read 
Often" applications.
As koha is such an app imho, it's not a too bad choice however !

-- 
Paul POULAIN
Consultant indépendant en logiciels libres
responsable francophone de koha (SIGB libre http://www.koha-fr.org)