Re: 4.0.22 to 5.x
Date: May 17, 2011 11:29PM
You will encounter any of several problems.
Plan A: Upgrade 4.0 -> 4.1 -> 5.0 -> 5.1 (and optionally -> 5.5) At each stage, run the update script. This sounds tedious.
Plan B: mysqldump all the data; install 5.x; load the data; work through the glitches. Recreate the user GRANTs.
Some possible glitches:
* lots of new keywords -- your code may say SELECT foo, where foo is a new keyword. Workaround is to add backtics: `foo`
* New tunables in my.cnf; probably none of them are critical.
* Charset issues. You are probably running latin1 now. If you need to switch to utf8, you could have data corruption issues.
* comma join vs explicit JOIN -- precedence changed
* on GRANTs, read about OLD_PASSWORD.
* There are lots of other "incompatible" changes; you probably won't hit many of them. Some of the changes will burn you regardless of how you do the upgrade.
That said, it is well worth it. There are many new features, and much increased stability in 5.x over 4.0. That's a decade of development.
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