Kentico provides some great documentation and directions on upgrading major versions.  Unfortunately, they can't perform their tests on every website scenario..  What I'm going to provide to you today is one very large tip when upgrading those older instances of Kentico.

Check the size of your database

Yes that's the big tip.  Check the size if your database before you start your upgrade.  If you have a large database and you have a somewhat standard or smaller website, you need to review this before performing your upgrade.  

Now the definition of "standard" and "smaller" are to be determined but really think about your site from a complexity standpoint and ask yourself these questions:

• Are you using any EMS features?
• If so, what features?
• Do you have analytics turned on?
• Do you store sent emails?
• Do you have versioning enabled?
•  

If you answered no to those questions and you have a large database size, double check those features to ensure they are not enabled.  

One of the first things you need to do is run a SQL script against your database to find which tables are the largest in rows and overall data.  For instance you could have 1000 emails in the cms_email table and the table size could be 1GB.  Then in your custom page type you have 1000 rows of data but only 400kb of data.  My point is, it's not always the row count.  Also check the data types in those large tables.  If you're storing files in the database, this will cause large table sizes as well.

In the past few weeks I've come across several Kentico 7 sites which had databases which were bloated with data which was not being used by the client.  One had analytics data in it which was not being used.  Another had 3.5 million records for contacts.  And yet another had 3 million activity records for contacts.  

When performing major upgrades to Kentico there are many tables which are dropped and recreated.  This means the tables data is stored in memory until the table is recreated.  This is where the trouble comes in.  If you have a 3 million record table that is 3 or 4 or 15GB in size, your upgrade will fail, guaranteed.  

Conclusion

If you're looking for a successful upgrade the first time with a version of Kentico prior to version 8, then check the size of your database and tables and ensure the features you're not using are disabled.

Best of luck and Happy Coding!