[Salesforce] Batchable instance is too big

I found the problem. The issue was the following:  My batch process had a global variable  which was keeping instances of lists of records that were created in each execution of the method "execute". Therefore I was unnecessarily accumulating records in memory and that caused the error "Batchable instance is too big" . 

 

I suggest you to check the status of the global variables after each execution and you may find the solution to your problem as well.