在INNODB引擎中进行事务处理

Question

Consider a transaction T1,

Start transaction;   
Update emp set emp_id=1 where emp_id=3;   
commit;

The engine i am using is INNODB engine.
Before commit operation of the above shown transaction, I had accessed the table again it is showing the previous committed values. If the Row Level locking is placed on the table, it might have shown the error ( you cannot access while some transaction is in the middle). Is there any wrong in my understanding.? Can any one help me on this?

Answer 1

Anything that is done as a part of a transaction is available to the same transaction even before the transaction is committed. The changes are not available in other transactions.

To test this, you need to update in one transaction and then from another terminal start a new transaction and try to access. The second transaction will be able to read the data but if you try to update the update will block and wait for the first transaction to be committed.

If you want the second select to wait and return the updated data you should use select for update.