Question

I have gone through the manual and it was mentioned that every transaction will add a BEGIN statement before it starts taking the dump. Can someone elaborate this in a more understandable manner?

Here is what I read:

This option issues a BEGIN SQL statement before dumping data from the server. It is useful only with transactional tables such as InnoDB and BDB, because then it
dumps the consistent state of the database at the time when BEGIN was issued without blocking any applications.”

Can some elaborate on this?

Answer 1

Since the dump is in one transaction, you get a consistent view of all the tables in the database. This is probably best explained by a counterexample. Say you dump a database with two tables, Orders and OrderLines

1. You start the dump without a single transaction.
2. Another process inserts a row into the Orders table.
3. Another process inserts a row into the OrderLines table.
4. The dump processes the OrderLines table.
5. Another process deletes the Orders and OrderLines records.
6. The dump processes the Orders table.

In this example, your dump would have the rows for OrderLines, but not Orders. The data would be in an inconsistent state and would fail on restore if there were a foreign key between Orders and OrderLines.

If you had done it in a single transaction, the dump would have neither the order or the lines (but it would be consistent) since both were inserted then deleted after the transaction began.