I am trying to insert a record in IBM DB2 DB. Upon insertion, a timestamp field is auto-generated. I have to take this value and send it via Kafka. I can only commit transaction if Kafka is successful, otherwise I rollback.
I am inserting using a native "INSERT" query.
REQUIREMENT: Want to get the auto-generated timestamp value without committing, so that I can rollback easily.
I tried flushing but that did not work.
What can I do?
session.flush() will work and get you the data if you query your DB. But these changes may not be visible in your Database visualizer (like Teradata) until you commit your transactions.
Hope that helped.
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 was updating the statement in Sqlplus and not commit the code. I am using exit to the terminal.
It is a simple update statement only but I am not commit the code.
Example: I was connected to SQL Plus using username and password.
UPDATE USER SET Name='Daniel' WHERE Name='Francis';
exit
Could you please guide me How to commit in another session or
Could you please update the possible suggestion.
Thanks
USER is a reserved keyword in SQLPLUS, you should use escape character.
Commit:
set exitcommit off
UPDATE "USER" SET Name='Daniel' WHERE Name='Francis';
exit
According to the Oracle docs, at least for version 10g, if your program quits without committing (and you haven't turned on autocommit), the transaction is automatically rolled back. Transactions are isolated at the session level so it is not possible to commit from a different session.
One thing I am uncertain on is whether a DDL statement will commit from a different session. The documentation suggests that a DDL statement forces a commit but it is not clear on the behavior across sessions. Most likely, a DDL statement will be blocked by another session's transactions, but it might be worth trying out.
If you do not explicitly commit the transaction and the program
terminates abnormally, then the last uncommitted transaction is
automatically rolled back.
I'm using Oracle SQL Developer tool, version 3.0.02 and I'm having some trouble understanding the following: if I Commit an update and the time response is '0 seconds' the commit is done properly? Because it happened a few times and the DB wasn't updated. I don't know if it's a coincidence or not. When I commit for the second time(just to be sure) after it shows me '0 seconds', it appears '0,016 seconds' and the update shows correctly. But I don't wanna commit 4 times in a row just to get it right. What do you guys think about this? Oh and it doesn't give me no errors.
Thank you in advance
The time taken by commit has nothing to do with any malfunctioning. The work is done by the query and commit just notes somewhere in the metadata that the transaction is finished. Commit does almost anything(just force to save on the disk some log files). If something gets wrong (i.e. commit don't work) you'll get an error.
The absence of the error signals that everything is ok, the database has done all you have asked to it.
For example, your updates may do nothing:
UPDATE db SET user='name' where file='name_of_file' and answer='okay' ;
if there is no file named 'name_of_the_file' with answer = 'okay' the database will do no work. And nothing to commit.
For the sake of a complete answer i'll add these points from this blog:
When a transaction is committed, the following occurs:
The internal transaction table for the associated undo table space records that the transaction has committed, and the
corresponding unique system change number (SCN) of the transaction is
assigned and recorded in the table
The log writer process (LGWR) writes redo log entries in the SGA's redo log buffers to the redo log file. It also writes the
transaction's SCN to the redo log file. This atomic event constitutes
the commit of the transaction
Oracle releases locks held on rows and tables
Oracle marks the transaction complete
You can check Oracle documentation to learn why commit is such a fast operation (rollback takes much longer, it has to refer to undo segments).
'Lost' commits may happen if somebody else commits their data, which appears to be the same as the 'old' data for you.
When is a row actually inserted into the database? Is it when "INSERT" statement is finished? or when "COMMIT" statement is finished after "INSERT" statement?
Later than you think. The principles here apply generally.
The whole point of the transaction log is to ensure ACID works in case of a power failure just as the INSERT finishes. The INSERT will be rolled forward or rolled back as part of the recovery phase (in most RDBMS)
So, it's more important that the transaction log entry is acknowledged as stored on the media. Then the INSERT can commit.
The data page containing the changed row will end up on disk eventually (checkpoint etc) but not necessarily at the point of successful commit.
However, the data page is in memory and available for use.
Note, an INSERT could cause a page split, indexes to be updated, triggers to fire etc so what I've said is simplified.
And it doesn't matter one way or the other when the data ends up on disk: as long as I can get the data and it's safe in case of, say, power failure
An oldie but still relevant for SQL Server: SQL Server 2000 I/O Basics
And what I've summarized is Write Ahead Logging
If you are running inside a transaction, when the transaction is committed. Otherwise, immediately.
Depends on the database/table implementation. It might just be when the transaction log is integrated - until which time the row is only inserted in the transaction log, and in memory.
insert into XYZ(col1, col2) values (1,2)
update XYZ set ... where col1 = 1
COMMIT
As in can see in the above code, we havent yet commited our insert statement, and we performed an update operation on the same row, and finally we commit the whole batch.
What exactly would happen in this case? Are there any chances of losing data in this scenario?
your session is always able to see its own modifications, even before you issue a commit.
the newly inserted row would by updated.
The only way you can "lose data" would be an interruption before the commit, in which case no operations would happen at all
The important words in Vincent's response are "your session".
A separate session will only see the unmodified data until you commit. That's part of read consistency means.
Depending on the frameworks and tools you're using, your session may get a lock on the record when you perform the update, preventing other sessions from updating it until you commit or rollback.
For further reading, here is a link to the "Data Concurrency and Consistency" section of the excellent Oracle Concepts Guide 10gR2
http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/consist.htm
Infact All transactions are stored in Rollback Segmant with in Table space memory of that particular instance.. A Rollback segment is a storage space within a table space that holds transaction information used to guarantee data integrity during a ROLLBACK and used to provide read consistency across multiple transactions.