Difference between SET autocommit=1 and START TRANSACTION in mysql (Have I missed something?)
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Published on 2010-06-01T14:38:48Z
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mysql
|transactions
Hey there, I am reading up on transactions in mysql and am not sure whether I have grasped something specific correctly, and I want to be sure I understood that correctly, so here goes. I know what a transaction is supposed to do, I'm just not sure whether I understood the statement semantics or not.
So, my question is, is anything wrong, (and, if that is the case, what is wrong) with the following:
By default, autocommit mode is enabled in mysql.
Now, SET autocommit=0;
will begin a transaction, SET autocommit=1;
will implicitly commit. It is possible to COMMIT;
as well as ROLLBACK;
, in both of which cases autocommit is still set to 0 afterwards (and a new transaction is implicitly started).
START TRANSACTION;
will basically SET autocommit=0;
until a COMMIT;
or ROLLBACK;
takes place.
In other words, START TRANSACTION;
and SET autocommit=0;
are equivalent, except for the fact that START TRANSACTION;
does the equivalent of implicitly adding a SET autocommit=0;
after COMMIT;
or ROLLBACK;
If that is the case, I don't understand http://dev.mysql.com/doc/refman/5.5/en/set-transaction.html#isolevel_serializable - seeing as having an isolation level implies that there is a transaction, meaning that autocommit should be off anyway?
And if there is another difference (other than the one described above) between beginning a transaction and setting autocommit, what is it?
Thanks a lot in advance for your help!
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