Transactions are not for critical data such as credit card numbers.  There
are at least a couple of reasons for transactions and neither of the
reasons I can think of are for storing critical data such as credit card

Transactions are for updates to the database that must happen all together
or not at all.  For example, if you enter a sale into a database, you might
have to enter the invoice and all the items purchased.  The invoice with no
purchased items makes little sense and purchased items with no
corresponding invoice makes little sense.  Without transactions, the
database could be left in an incomplete state if records were inserted
(deleted, or changed) that depend upon other records being inserted
(deleted, or changed).

Also, the transaction log is used by the database to bring it into a state
of integrity in the event of a crash.  The log can be rolled back to the
last state that the database knew it was complete and had integrity.  This
is not usually something the database user/programmer does,'s
more dba or system oriented.

So transaction support is basically crucial for database integrity.  The
MySQL folks didn't even add support for transactions until just a couple of
releases ago, and that was because many people demanded it.  When they
released it, it was (ummm...and still is) some kind of amalgamation of
several products.

I don't understand why MySQL would be better at handling table crashes and
data corruption.  Perhaps the fact that Jon simply spewed marketing hype
(FUD) regarding transactions and what they're good for is an indication
that the statement about MySQL being better at handling crashes and
corruption is just more baseless marketing hype.

None of the above means that MySQL is a bad or undesirable product.  I
sometimes use MySQL.  It has come a long way in a very short amount of
time, and they're doing fantastic things to it.  However, one should not
put it on a pedestal and exhalt it above all else.  

One might also not try too hard to compare MySQL to PostgreSQL.  One of
these products is a relational database management system.  The other is a
quasi-SQL-like-front-end-to-systems-of-indexed-files that has never
concerned itself with things like standards conformance.

Performance was addressed in another post.  But I wish to remind all
reading this that raw speed on a transaction or two is probably pretty
nice, but being able to perform adequately under load is another matter
entirely.  One of these qualities is cool, but lack of the other quality is
a disaster and could get you a pink slip or a torn up contract.

One "answer" to the original post would be to use whichever product suits
your needs.  Both are highly acclaimed.  Both have their strengths and
weaknesses.  Neither is a clear "winner" over the other.  There are many
reasons to select a platform...among them are things like:

 * your abilities
 * the abilities of the talent pool available to you
 * suitability to a task
 * features
 * security
 * scalability
 * portability

And in Matt's case, it may be that MySQL is the one that should be used.
But certainly unfounded hype is not among the reasons anyone should select
a platform.


At 10:22 AM 4/7/01 +0200, Jon Valvatne wrote:
>On the contrary, MySQL is much better at handling table crashes and data
corruption than PostgreSQL is. What you may have heard is that due to lack
of transaction support, critical data may be lost "in transit" from your
application to the database, in the event of a system crash or a dropped
connection. Well, guess what? MySQL now supports transactions in its latest
release. Using transactions is probably not really needed though, unless
your data is critical, such as credit card numbers.
>As for a full comparison between the two, I think the bottom line is that
MySQL is slightly more light-weight, but easier to use and faster than
PostgreSQL. So if you're looking for a database for a relatively
noncritical web application, I'd say go with MySQL, especially since that's
what you already have experience with.
>One of the upcoming features in MySQL I'm really looking forward to is
query caching, which is a great feature for web applications.
>Jon Valvatne
>> Can someone outline the differences between the two? I am partial to MySQL
>> from experience but want to get a good view of why one is better than the
>> other.
>> Also, I've heard that you will lose data with MySQL if a system failure
>> should occur.
>> Thanks.
>> Matt

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