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Re: MySQL 5 : safe update ?

Frédéric VANNIÈRE wrote:
Is there compatibilities problems between MySQL 4.1 and MySQL 5.0 ?
The one obstacle that will *prevent* your upgrade from even completing is that MySQL 5 doesn't read ISAM (".ISA") files anymore. If you have any ISAM files (probably created with versions of MySQL 3 or earlier), then you have to convert them to MyISAM or InnoDB. I have a script that does this if you need.

When I tried to move to MySQL 5 a few weeks ago, I ran into a little snafu with this. The system will let you remove MySQL 4 and install MySQL 5 *without* checking to see if you have legacy ISAM tables. When the MySQL 5 installer script sees them, however, it refuses to run the new daemon. So, you're left with version 5 of the daemon which won't run because some of your tables are in the old format, but you have no way of converting them to the new format because version 5 doesn't read the old format.

The only solution is to downgrade to version 4.... *but* there's a problem. The version 5 installer places a file in /var/lib/mysql called debian-5.0.flag. When the 4.x installer sees this, it refuses to install. *So*... you have to delete that debian-5.0.flag, then downgrade, then convert your ISAM tables to MyISAM, and then upgrade again.

Of course, you can avoid all of this by just converting to MyISAMs before you even try the upgrade to MySQL 5.
I need to move 4000 databases from one server to another (dump then import)
You don't have to dump and import (unless you really want to). You can actually just copy over your entire /var/lib/mysql to the other server.
I'm wondering if I can use MySQL 5 on the new server without breaking my customer's
There are a variety of subtle changes. You can read about them here:


Apparently, they have a tool called mysql_upgrade that checks your tables for any incompatibility issues.

Lastly, you might want to give a little more attention to the changes to the SQL language in version 5, since these could affect some of the SQL statements used by your customers in their applications.

- Joe

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