how can i make database consistent in this situation?

Question

I have problem while dealing with copy of database table entry from one file to other .

suppose i have two tables called one.sql , two.sql , now i wana transfer some record from one.sql to the table two.sql, then delete that entry from one.sql ater copying success.

problem : suppose power was gone after i make copy from one to two, the delete record from one wasnt done , here in that case same record will be in both tables. that i dont want. so in this situation how to handle these types of inconsistent on fly.

Answer 1

Your RDBMS is not a simple datastore! It supports journaling , transaction isolation and atomic updates . So...

... with transactional tables ( InnoDB ) and with decent isolation level simply do:

START TRANSACTION -- Or SET autocommit = 0
INSERT INTO two SELECT * FROM one WHERE ...;
DELETE FROM one WHERE ...;
COMMIT

COMMIT will atomicity apply the changes to the DB. That is, from the other transactions point of view, the move is either done or not started . No one can see it half done . Even in case of catastrophic failure (power outage).

Of course, if you move all your records, you could also rely on RENAME TABLE ...

Answer 2

You can use transaction blocks to descrease unexpected results at some degree. But solving a power problem is another thing.

You can however use a batch and check if two tables don't contain same records at some interval, if you are worried about a power problem.