Expected to open 2 undo tablespaces but was able to find only 0 undo tablespaces.

We recently tried setting innodb_undo_tablespaces=2 for our mysql 5.7 server. But during the restart the server returned with:

[ERROR] InnoDB: Expected to open 2 undo tablespaces but was able to find only 0 undo tablespaces. Set the innodb_undo_tablespaces parameter to the correct value and retry. Suggested value is 0

It turns out this is already documented : "The number of innodb_undo_tablespaces must be set prior to initializing InnoDB. Attempting to restart InnoDB with a greater number of undo tablespaces than you specified when you first created the database will result in a failed start and an error stating that InnoDB did not find the expected number of undo tablespaces."

What does "first created the database" mean? Does the documentation mean a fresh installation of mysql where there are no databases within the server? Is there a way to bypass this requirement?

 

Answers:

 

Probably refers to "fresh installation".

The workaround is painful...

1. Dump all the data.
2. Stop mysqld.
3. Blow away ibdata1 and iblogs.
4. Change the setting in my.cnf.
5. Restart. (This should feel like a 'fresh' install.)
6. Reload the data.

Do you have some indication that changing that setting will help you significantly? If so, please explain. It is a very new feature, and is there for a reason, but not many users need it.

 

 

解决方法：删掉ibdata1再重启