划界交易是什么意思？

Question

What is meant by demarcate transactions ? When we talk about distributed transactions ? Can someone please give me an example so far I only know that it use some code of pseudo code EOT BOT but I have no idea what these are ? Why we need demarcate transactions ?

Answer 1

In pseudo-code:

BEGIN TRANSACTION

# modify data here
# possibly taking multiple seconds, minutes, or hours
# during which other users are concurrently modifying 
# data in the system, including the same data records 
# this transaction is modifying

END TRANSACTION

The BEGIN TRANSACTION and END TRANSACTION commands demarcate the transaction. They define what operations are "the transaction." Namely, the operations that occur between them. The END TRANSACTION in real code is usually going to be a COMMIT TRANSACTION or ROLLBACK TRANSACTION type of statement.

You need to demarcate transactions because they might not be a single statement. So you need a way to group multiple statements together, then treat them as a single logical operation. For example:

BEGIN TRANSACTION
UPDATE accounts SET balance = balance + 100000 WHERE acct_id = 10231212
DELETE FROM deposits WHERE deposit_id = 32984727922121
COMMIT TRANSACTION

If you add a deposit to an account but don't delete it from the list of incoming deposits, that's a bad, bad, bad error for which the recipient will thank you but the bank will not.