Say I have a query like this:
BEGIN Transaction
UPDATE Person SET Field=1
Rollback
There are one hundred million people. I stopped the query after twenty minutes. Will SQL Server rollback the records updated?
A single update will not update some rows. It will either update all or 0.
So, if you cancel the query, nothing will be updated.
This is atomicity database systems which SQL Server follows.
In other words, you don't have to do that rollback at the end, nothing was committed anyway.
When you cancel a query, it will still hold locks until everything is rolled back so no need to panic.
You could test it yourself, execute the long query, cancel it and you will notice that it takes a while before the process really end.
While the update statement will not complete, the transaction will still be open, so make sure you rollback manually or close out the window to kill the transaction. You can test this by including two statements in your transaction, where the first one finishes and you cancel while it's running the second - you can still commit the transaction after stopping it, and then get the first half of your results.
BEGIN Transaction
UPDATE Person SET Field=1 WHERE Id = 1
UPDATE Person SET Field=1
Rollback
If you start this, give it enough time for the first line to finish, hit the Stop button in SSMS, then execute commit transaction, you'll see that the first change did get applied. Since you obviously don't want part of a transaction to succeed, I'd just kill the whole window after you've stopped it so you can be sure everything's rolled back.
Since you have opened the Transaction, Stoping the Query manually does not completes the transaction, This transaction will still be open and all the subsequent requests to this table will be blocked.
You can do any one of following options
Kill the Connection using the command KILL SPID (SPID is the process ID of your connection)
Note: This will auto rollback the changes you made, you can monitor the rollback status with command KILL SPID WITH STATUSONLY (After killing)
run the ROLLBACK command manually
** SPID is your request id, you can find it from sys.sysprocesses table/ you can also find it on Management Studio query Window the number which is within brackets / also you can find it at bottom right corner of your management studio beside the login name.
Example SQLQuery2.sql... (161) -- 161 is your spid.
Related
I executed a simple SQL performance query to retrieve the sessions running currently in the database in Oracle sql developer.
But accidentally my cursor clicked on the roll back icon and it got rolled back.
Could you please tell me What happens to the entire database after this?
Rolling back a select does nothing as long as you didn't make changes to the database without committing the transaction.
In oracle clients when you run a query that modifies the database, the query is first run. Another step is then needed to commit the transaction.
MS SQL Server has a similar concept where you can do safe transactions like
begin tran
delete from table where val > 5
rollback{commit}
This allows you to look at the number of records your SQL statement have done prior to committing the transaction. If you want you can choose to rollback or commit your transaction.
What exactly did you roll back? That "simple SQL performance query", or "sessions running currently in the database in Oracle SQL Developer"?
If former, nothing happened, SELECT didn't do any changes anyway. If it were SELECT ... FOR UPDATE, lock would have been released.
If latter, then any changes you did in the database since previous COMMIT were rolled back (as you didn't roll back to a savepoint), so - nothing happened either.
What happens to the entire database after this?
It returned to state it was in earlier, as if you didn't touch anything at all.
I executed an update statement mistakenly without any where clause in pl/sql developer.I did click on the break button when I found what had happened after some time when the execution was taking time to complete, commit and rollback buttons were grayed out after breaking the execution hence could not roll back the transaction. I am worried if break button commits the transaction in pl/sql developer or it roll backs to the previous state.
PL/SQL Developer's Break key does not commit, it just breaks the current operation and leaves things as they were at the start of it, including any open transactions. For example, if you did three updates without committing, and then started a fourth but used the Break key to interrupt it, you would still have the first three uncommitted updates, and the Commit and Rollback icons would be active.
The icons were greyed out because there was no transaction to commit. PL/SQL Developer sets their status by calling dbms_transaction.local_transaction_id after every statement to check for an open transaction.
If you didn't see the "Are you sure?" warning popup, you might check Configure > User Interface > Options > DSA Dialogs in case you previously clicked "OK" on a "Don't show this message again" popup.
First step is to be cool.. otherwise you won't able to think properly.
Immediately execute Rollback command.
Then run a query to select the updated field and check whether the result contains any values other than updated value.
for example if you executed below query,
update Employees set Status = 'Inactive' you should check whether the status column contains any value other than 'Inactive'
If the column contains any value other than updated value, you are good and fine.
the system rolled back that update statement.
If the column doesn't contains value other than the updated values, please connect with the database administrator to rollback this transaction.
They will able to do this without much hassle.
I have a series data modify operation to do,such as
1. update table_a set value=1 where id=1
2. update table_b set value=2 where id=1
3. update table_c set value=3 where id=1
and I want to ensure this three operation must all complete,I know using transaction can guarantee all performed or none performed.But my point is must make these three all performed.when first sql performed,the app instance may crashed and the other two are missed.
Note this is a ditributed enviroment,may be another app instance can take over the unfinished SQL,but how can I do it?
Can I use a stored procedure,the app instance only fire the stored procedure,and database finsh all the sql?
If when performing transaction,the app instance suddenly crashes,will it leads to a dead lock?
Deadlocks are not crashed requests which fail before the end of the execution. If your request crashes into a transaction, it won't lead to a deadlock.
It is always better to use stored procedures but this won't help you for this specific case.
What I would suggest is inded the use of a transaction with a try catch to rollback the transaction in case of failure.
Something like that :
BEGIN TRY -- start of try
BEGIN TRANSACTION; -- start of transaction
update table_a set value=1 where id=1
update table_b set value=2 where id=1
update table_c set value=3 where id=1
COMMIT TRANSACTION; -- everything went ok we commit
BEGIN CATCH -- an error happened we rollback
PRINT N'Unexpected error';
ROLLBACK TRANSACTION;
END CATCH
You can check more complete examples here
If an app is performing a transaction on a database server, and the app crashes (abruptly disconnects from the database) before committing the transaction, the database server rolls back the transaction. The disconnection does not leave the database in an unusable (potentially deadlocked) state.
So your database contents won't reflect any of your three UPDATE operations when your app crashes during your transaction. It will just lose the transaction in progress.
How to handle this potential failure mode?
Reduce the probability of a crash during a transaction. Try to avoid doing stuff in your app that could make it crash while your transaction is in process. For example, if you get data from some other server or device, get it all before you begin your transaction. This solution is usually good enough for production apps.
Rig up some sort of way for your app, upon restarting, to find out the most recent successful transaction. One good way? Add a column like this to one of your tables: (this is a MySQL thing.)
last_update_timestamp TIMESTAMP DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
This causes every UPDATE operation on each column to -- automatically -- put NOW() into the last_update_timestamp column. Then, when your crashed app restarts you can do
SELECT MAX(last_update_timestamp) FROM table
and you'll know when the most recent successful update occurred. This automatic update also gets rolled back if a transaction is rolled back. If you know when the last successful update occurred, your app may be able to redo the one that was rolled back by the crash.
If you choose to build a redo-transaction capability, be sure to build it so you can test it! if (testingAppCrash) crashNow = 1 / 0; might do the trick in your app.
I want to know how to stop undo process of oracle ? I tried to delete millions of rows of a big table and in the middle of process I killed session but It started to undo delete and for a bout two hours database got dramatically slow. I didn't want the undo process to be continued. Is there any way to stop it ?
You can't stop the process of rolling back the transaction because doing so would leave the database in an inconsistent state.
When you are executing a long-running delete process, Oracle will likely be writing the changed blocks to your data files before you decide whether to commit or rollback the transaction. If you interrupted the process in the middle of executing the transaction, there will be some changed blocks on disk, some changed blocks in memory, and some unchanged blocks. Rolling back the transaction is the only way to return the database to the state it was in before you started executing the DELETE statement.
Row-by-row delete processes can, as you've found, be exceedingly slow. If the deletions are all done in a single transaction, as appears to be the case here, they can become even slower. You might want to consider the following options:
If you're deleting all the rows in the table you might want to consider using the TRUNCATE TABLE statement.
If you're not deleting all the rows in the table you should probably change your procedure to COMMIT after a certain number of rows are deleted.
In the meantime you're going to have to wait until that rollback process completes.
Share and enjoy.
and when you try truncating the table while it's still deleting you'll be seeing an ORA-00054 "resource busy and acquire with NOWAIT specified or timeout expired"
A few minutes ago, while working out a new sproc, I executed the wrong delete statement. Something like this:
Delete From SomeTable Where SomeStatusID=1
10 seconds into it, I realized that I typed in the wrong status and hit cancel. It said that the statement was canceled.
I did a restore to a separate database to get back the table that I just presumably nuked, thinking that since this was not in a transaction some records were probably deleted.
Oddly, the records were all intact. Just curious as to why this was -- did it treat the individual delete statement as a transaction in this case, even though there was not an explicit transaction defined?
By default, a single DML statement is executed as a transaction. If the statement succeeds, the transaction is committed. If the statement is cancelled or otherwise fails, the transaction is rolled back.
This behavior is built in to the engine, and is not related to management studio. See Autocommit Transactions in the docs.
There are always transactions. The only thing that changes is how those transactions are isolated from each other and that in management studio the transaction might not be defined explicitly and is auto-committed when the query finishes.