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• it is assumed, that BinaryTuple protocol will not changed, . Otherwise, we will need have to implement data conversion code a solution to convert data explicitly, when row is upgraded.
• all storage engines are compatible this feature. Otherwise, we will need a workaround, e.g. to fallback to a slow blocking solution.
• user may experience unexpected transactions transaction rolling back for long transactions, which overlap the change column type operation.
  
  

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