Removing innodb indexes cause db to crash.

I have a server with 32Gb rams in it. I have given almost 70% innodb buffer pool to it. I have table with almost 40 millions data in it. Recently I tried to remove of the index and I tried to replace it with another. My whole system could not work any more all it not able to see my db.

I could see this errors alot in my application.

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after statement closed.

So I had to stop the db truncate the whole table and start a fresh. Is this a innodb limitation in future what can I do and what other the limitation I need to be known further?

Is it a good reason for my to swap to tokudb with this scenario ?

We will need more information though. Please share your error log at the time before/during/after the table alter to drop index. Also Percona/MySQL server version and my.cnf will help too.