Installing MySQL - Learning MySQL - page 70

Fixes for bugs
No complex software such as MySQL can be free of bugs; over time, people dis-
cover unexpected behavior, or possible data corruption. As these problems come
to light, they are fixed for the latest version. MySQL bugs are reported and analyzed
at the http://bugs.mysql.com web site. You can use this web site to view the bug
reports for your MySQL version and determine whether any are likely to affect your
operations.
Fixes for security vulnerabilities
Security vulnerabilities are an especially dangerous class of bug; by exploiting a
vulnerability, an attacker could gain unauthorized access to data, or render your
system unusable (cause a denial of service). If your server is connected to a network
or otherwise accessible to people other than yourself, you need to take security
issues very seriously.
Improved features
As software matures, new features are added to make some tasks easier or to im-
prove efficiency. For example, MySQL 5.0 introduced support for views (virtual
tables), stored procedures (predefined queries that clients can call), cursors (pointers
to the result of database operations), and triggers (predefined operations that are
carried out automatically before or after a row is inserted, deleted, or updated).
Similarly, subqueries (nested SELECT queries) were not possible in MySQL before
version 4.1; neither were multiple concurrent character sets.
Some new features could greatly simplify your application, allowing you to reduce
development time by simply upgrading your MySQL server. On a related note,
application software that you might want to use with your database server—for
example, a free web portal system—might require you to have a minimum version
of MySQL.
Newer versions of MySQL are generally backward-compatible with recent versions—
that is, older ways of doing things will continue to work. A new server can work with
old data, and even with older clients. For example, MySQL password management was
improved in version 4.1.0. The new server can correctly handle passwords stored in
the old format, and, if it's started with the old-passwords option, it can modify its
behavior to cater to older clients, such as a web server that uses the old mechanism.
However, software is generally not upward-compatible—that is, you're more likely to
have difficulty if moving from a newer version of MySQL to an older version, especially
if they are major versions apart (for example, moving from MySQL 5.0 to MySQL 4.1).
It's hard to find cases where downgrading is warranted.
You should assess your own needs and decide whether an upgrade is necessary or
worthwhile; if, for example, you have an online shopping application that's running
perfectly, you would only need to upgrade if you wanted to make changes that would
be easier done with a newer MySQL version or if you learn of bugs that could affect the
reliability or security of your site. Upgrading a MySQL server could require upgrades