I've been asked to try to roll back some database changes if there was an error.
Before I even start trying to use a TRANSACTION with either COMMIT or ROLLBACK, could someone tell me if I can do the following in MS Access?
void Start() {
try {
AccessDatabaseOpen(); // Opens the access database
foreach (File in FileList) {
AccessTransactionStart(); // Starts the Transaction
AccessWriteSectionDataFromFile();
AccessWriteEmployeeDataFromFile();
AccessWriteSomethingElseFromFile();
} // go to next File in FileList
AccessTransactionCommit();
} catch {
AccessTransactionRollback();
} finally {
AccessDatabaseClose();
}
}
The syntax is crappy, but you should get the point: Can a routine in code start a transaction, call several other routines, and either commit or rollback the whole thing or is this idea make believe?
Thanks,
Joe
Can a routine in code start a
transaction, call several other
routines, and either commit or
rollback the whole thing
Yes, this is the basic idea of transaction handling and your outlined example would be a standard approach to deal with them from code. Details will vary depending on particular situation/needs and of course the database system used (e.g. nested transactions, scope, concurrency handling, etc.).
If a database abstraction layer is involved, check for specifics of that, as they often come with some implicit transaction handling that can often be configured by some settings/parameters.
Related
Most of the code implementing transactions I come across, call Rollback explicitly. Do we need to call Rollback? Doesn't Dispose call Rollback automatically? What's the purpose of explictly calling Rollback?
Thanks all.
public void DatabaseUpdate ()
{
using var MyTransaction = MyContext.Database.BeginTransaction () ;
if (MethodIsSuccessful ())
{
MyTransaction.Commit () ;
}
else
{
// MyTransaction.Rollback () ; // Not necessary, will be called by Dispose, right ?
}
}
Dispose() does not call Rollback(), it merely cleans up the transaction object and ensures the Entity Framework is no longer using that transaction.
So that brings us to the database. The Sql Server documentation states that
Depending on the current transaction isolation level settings, many resources acquired to support the Transact-SQL statements issued by the connection are locked by the transaction until it is completed with either a COMMIT TRANSACTION or ROLLBACK TRANSACTION statement. Transactions left outstanding for long periods of time can prevent other users from accessing these locked resources, and also can prevent log truncation.
So yes, you do need to call Rollback() explicitly, if that is your intention.
I'm using NServiceBus to handle some calculation messages. I have a new requirement to handle calculation errors by writing them the same database. I'm using NHibernate as my DAL which auto enlists to the NServiceBus transaction and provides rollback in case of exceptions, which is working really well. However if I write this particular error to the database, it is also rolled back which is a problem.
I knew this would be a problem, but I thought I could just wrap the call in a new transaction with the TransactionScopeOption = Suppress. However the error data is still rolled back. I believe that's because it was using the existing session with has already enlisted in the NServiceBus transaction.
Next I tried opening a new session from the existing SessionFactory within the suppression transaction scope. However the first call to the database to retrieve or save data using this new session blocks and then times out.
InnerException: System.Data.SqlClient.SqlException
Message=Timeout expired. The timeout period elapsed prior to completion of the >operation or the server is not responding.
Finally I tried creating a new SessionFactory using it to open a new session within the suppression transaction scope. However again it blocks and times out.
I feel like I'm missing something obvious here, and would greatly appreciate any suggestions on this probably common task.
As Adam suggests in the comments, in most cases it is preferred to let the entire message fail processing, giving the built-in Retry mechanism a chance to get it right, and eventually going to the error queue. Then another process can monitor the error queue and do any required notification, including logging to a database.
However, there are some use cases where the entire message is not a failure, i.e. on the whole, it "succeeds" (whatever the business-dependent definition of that is) but there is some small part that is in error. For example, a financial calculation in which the processing "succeeds" but some human element of the data is "in error". In this case I would suggest catching that exception and sending a new message which, when processed by another endpoint, will log the information to your database.
I could see another case where you want the entire message to fail, but you want the fact that it was attempted noted somehow. This may be closest to what you are describing. In this case, create a new TransactionScope with TransactionScopeOption = Suppress, and then (again) send a new message inside that scope. That message will be sent whether or not your full message transaction rolls back.
You are correct that your transaction is rolling back because the NHibernate session is opened while the transaction is in force. Trying to open a new session inside the suppressed transaction can cause a problem with locking. That's why, most of the time, sending a new message asynchronously is part of the solution in these cases, but how you do it is dependent upon your specific business requirements.
I know I'm late to the party, but as an alternative suggestion, you coudl simply raise another separate log message, which NSB handles independently, for example:
public void Handle(DebitAccountMessage message)
{
var account = this.dbcontext.GetById(message.Id);
if (account.Balance <= 0)
{
// log request - new handler
this.Bus.Send(new DebitAccountLogMessage
{
originalMessage = message,
account = account,
timeStamp = DateTime.UtcNow
});
// throw error - NSB will handle
throw new DebitException("Not enough funds");
}
}
public void Handle(DebitAccountLogMessage message)
{
var messageString = message.originalMessage.Dump();
var accountString = message.account.Dump(DumpOptions.SuppressSecurityTokens);
this.Logger.Log(message.UniqueId, string.Format("{0}, {1}", messageString, accountString);
}
I've been working on this for about a day and a half now, and searched numberous blogs and help articles on the Web. I found several questions on SO related to this error, but I didn't think they quite applied to my situation (or in some cases, unfortunately, I couldn't understand them well enough to implement :P). I'm not sure I can describe this well enough for help... but here goes:
We have a .NET app to track our resources. There's an export function to copy a resource to the time tracking system and the billing system; this accesses a stored procedure that links to the time and billing databases.
I recently moved the billing system database to a new server (original server: Server 2003 SP2, SQL 2005; new server: Server 2008 R2, SQL 2008 R2). I have a Linked Server set up that points to the 2008 databases. I updated the stored procedure to point to the 2008 server, and then I got an error about MSDTC and RPC (http://www.safnet.com/writing/tech/archives/2007/06/server_myserver.html). I enabled 'rpc/rpc out' on the Linked Server and set MSDTC to allow Network Access (something like this: http://www.sqlwebpedia.com/content/msdtc-troubleshooting).
Now I'm getting the above, when I try to run the export function: "This SqlTransaction has completed; it is no longer usable." What seems odd to me is that when I just run the stored procedure (from SSMS), it says it completes successfully.
Has anyone seen this before? Have I missed something in the configuration? I keep going over the same pages, and the only thing I found was that I didn't reboot after making the MSDTC changes (mentioned in here: http://social.msdn.microsoft.com/forums/en-US/adodotnetdataproviders/thread/7172223f-acbe-4472-8cdf-feec80fd2e64/).
I can post part or all of the stored procedure, if it would help... please let me know.
I believe this error message is due to a "zombie transaction".
Look for possible areas where the transacton is being committed twice (or rolled back twice, or rolled back and committed, etc.). Does the .Net code commit the transaction after the SP has already committed it? Does the .Net code roll it back on encountering an error, then attempt to roll it back again in a catch (or finally) clause?
It's possible an error condition was never being hit on the old server, and thus the faulty "double rollback" code was never hit. Maybe now you have a situation where there is some configuration error on the new server, and now the faulty code is getting hit via exception handling.
Can you debug into the error code? Do you have a stack trace?
I had this recently after refactoring in a new connection manager. A new routine accepted a transaction so it could be run as part of a batch, problem was with a using block:
public IEnumerable<T> Query<T>(IDbTransaction transaction, string command, dynamic param = null)
{
using (transaction.Connection)
{
using (transaction)
{
return transaction.Connection.Query<T>(command, new DynamicParameters(param), transaction, commandType: CommandType.StoredProcedure);
}
}
}
It looks as though the outer using was closing the underlying connection thus any attempts to commit or rollback the transaction threw up the message "This SqlTransaction has completed; it is no longer usable."
I removed the usings added a covering test and the problem went away.
public IEnumerable<T> Query<T>(IDbTransaction transaction, string command, dynamic param = null)
{
return transaction.Connection.Query<T>(command, new DynamicParameters(param), transaction, commandType: CommandType.StoredProcedure);
}
Check for anything that might be closing the connection while inside the context of a transaction.
Had the exact same problem and just could not find the right solution.
Hope this helps somebody.
I have an .NET Core 3.1 WebApi with EF Core. Upon receiving multiple calls at the same time, the applications was trying to add and save changes to the database at the same time.
In my case the problem was that the table that the data would be saved in, did not have a primary key set.
Somehow EF Core missed when the migration was ran from the application that the ID in the model was supposed to be a primary key.
I found the problem by opening the SQL Profiler and seeing that all transactions was successfully submitted to the database (from the application) but only one new row was created. The profiler also showed that some type of deadlock was happening but I couldn't see much more in the trace logs of the profiler.
On further inspection I noticed that the primary key identifier was missing on the column "Id".
The exceptions I got from my application was:
This SqlTransaction has
completed; it is no longer usable.
and/or
An exception has been raised that is likely due to a transient
failure. Consider enabling transient error resiliency by adding
'EnableRetryOnFailure()' to the 'UseSqlServer' call.
I have the same problem. This error occurs because conection pooling. When exists two or more users acess the system the connetion pooling reuse a connetion and the transation too. If the first user execute commit ou rollback the transaction is no longe usable.
I have recently ran across similar situation. To debug in any VS IDE version, open exceptions from Debug (Ctrl + D, E) - check all checkboxes against the column "Thrown", and run the application in debug mode. I have realized that one of the tables was not imported properly in the new database, so internal Sql Exception was killing the connection, thus results into this error.
Gist of the story is, If Previously working code returns this error on a new database, this could be database schema missing issue, realize by above debugging tip,
Hope It Helps,
HydTechie
Also check for any long running processes executed from your .NET app against the DB. For example you may be calling a stored procedure or query which does not have enough time to finish which can show in your logs as:
Execution Timeout Expired. The timeout period elapsed prior to
completion of the operation or the server is not responding.
This SqlTransaction has completed; it is no longer usable.
Check the command timeout settings
Try to run a trace (profiler) and see what is happening on the DB side...
In my case the problem was that one of the queries included in the transaction was raising an exception, and even though the exception was "gracefully" handled, it still managed to roll back the entire transaction.
My pseudo-code was like:
var transaction = connection.BeginTransaction();
for(all the lines in a file)
{
try{
InsertLineInTable(); // INSERT statement might fail and throw an exception
}
catch {
// notify the user about the error on line x and continue
}
}
// Commit and Rollback will fail if one of the queries
// in InsertLineInTable threw an exception
if(CheckTableForErrors())
{
transaction.Commit();
}
else
{
transaction.Rollback();
}
Here is a way to detect Zombie transaction
SqlTransaction trans = connection.BeginTransaction();
//some db calls here
if (trans.Connection != null) //Detecting zombie transaction
{
trans.Commit();
}
Decompiling the SqlTransaction class, you will see the following
public SqlConnection Connection
{
get
{
if (this.IsZombied)
return (SqlConnection) null;
return this._connection;
}
}
I notice if the connection is closed, the transOP will become zombie, thus cannot Commit.
For my case, it is because I have the Commit() inside a finally block, while the connection was in the try block. This arrangement is causing the connection to be disposed and garbage collected. The solution was to put Commit inside the try block instead.
For what it's worth, I've run into this on what was previously working code. I had added SELECT statements in a trigger for debug testing and forgot to remove them. Entity Framework / MVC doesnt play nice when other stuff is output to the "grid". Make sure to check for any rogue queries and remove them.
In my case, I've some codes which need to execute after committing the transaction, at the same try-catch block. One of the codes threw
an error then try block handed over the error to its catch block which contains the transaction rollback.
It will show a similar error. For example, look at the code structure below :
SqlTransaction trans = null;
try{
trans = Con.BeginTransaction();
// your codes
trans.Commit();
//your codes having errors
}
catch(Exception ex)
{
trans.Rollback(); //transaction roll back
// error message
}
finally
{
// connection close
}
Hope it will help someone :)
When executing an NServiceBus handler that uses NHibernate for its data access operations, I am seeing an error that I am not sure if I need to be concerned with.
The handler has code that does something like this:
using (var tx = Session.BeginTransaction())
{
var accountGroup = _groupRepository.FindByID(message.GroupID);
accountGroup.CreateAccount(message.AccountNumber);
tx.Commit();
}
When I profile this process, I see the following lines:
enlisted session in distributed transaction with isolation level: Serializable
begin transaction with isolation level: Unspecified
SELECT ... FROM AccountGroups this_ WHERE this_.ID = 123
INSERT INTO Accounts ...
commit transaction
commit transaction
The first commit message is generated by my code when I call tx.Commit(). The second commit message, I believe occurs when we leave the Handle method of the handler and is called by NServiceBus. This second call to commit generates an alert in NHProf that states "Using a single session in multiple threads is likely a bug".
I don't think this is an issue, because there really is nothing to commit at that time, but am I doing some inappropriate here? I do want to run my code within a transaction, but when I do, I get this alert.
Any ideas?
This isn't an issue, what is happening is that NH Prof detects that the DTC commit is happening in another thread.
It should actually handle DTC commits properly, so I am not sure what is going on. At a guess, using both DTC commit and standard commit it confusing it.
I'll fix it.
I am trying to use NHibernate with legacy entities that are not mapped with NHibernate. On occasion this means that I need to manually flush NHibernate data to the database so that I don't receive foreign key exceptions when I try to connect the legacy entities with NHibernate-mapped entities.
A problem occurs when this takes place within a transaction that then needs to be rolled back. The data flushed from NHibernate does not rollback.
Is there anything I can do about this?
UPDATE
Still curious how to do this - I don't believe either of the answers given address the issue. I need to call Flush(). The question is, how do I rollback data that has been flushed?
check this: Force query execution without flush/commit
I seemed to have the same problem, i would flush and then i would rollback but some data would remain persisted in the database. However, there were some parts in my code that would call a commit, which cannot be rolled back. Consider the accepted answers' code snippet as the proper usage for transactions, flushes, rollbacks and commits and take into consideration that this pattern can be extended...
in a single unit of work (ie we consider a Request in a web application as a single unit of work and everything that happens in that request exists in a single transaction which onEndRequest is committed):
you call _sessionFactory.OpenSession(), _session.BeginTransaction(), _session.CommitTransaction() and _session.CloseSession() only once.
you can call _session.Flush() and _session.RollBackTransaction() as many times as you want, but Flush() is automatically called on Commit automatically. You may want to call a Flush when you need to make a query and ensure that the data fetched will not be stale.
Note that once a commit transaction is committed, all operations afterwards do not happen on that transaction. Instead NHibernate will create the necessary transaction under the hood (http://www.nhprof.com/Learn/Alerts/DoNotUseImplicitTransactions) in which point
you already have problems tracking consistency and possibly logical integrity
If you really must call commit in the middle of your unit of work it is strongly advised to create a new transaction at that point so you can manage it explicitly
What's even better is to try out Nested Transactions will allegedly allow partial commits; you can rollback the "root" transaction and all changes will be reverted. I haven't really tested this feature of .NET and SQL Server, although the nested transaction in the database itself leaves a lot to be desired and i don't know how exactly ADO.NET instruments this feature.
points 1 to 4 have been tested with all versions of NHibernate starting from 1.2.
For the sake of formatting I allow myself to update tolism7's answer here.
use using and forget about transaction.Dispose() - the transaction will automatically be Dispose'd of at the end of the using block.
throw - don't throw ex because it means throwing away your stacktrace (see this post where it states "When the .NET Framework executes this statement: throw ex; it throws away all the stack information above the current function.")
.
public void CommitChanges()
{
using (var transaction = Session.BeginTransaction()) // <-- open scope
try
{
// do something
transaction.Commit();
}
catch (HibernateException)
{
transaction.Rollback();
_session.Close();
_session.Dispose();
throw; // <-- this way the stacktrace stays intact!
}
}
A VB.NET version of this piece of code can be found here.
When using transactions with NHibernate try to avoid using the Session.Flush() and instead use the transaction.Commit() which it calls the session.flush() internally.
If during the Commit() an error occurs and the transaction needs to be rolled back this can be addressed like this.
public static void CommitChanges()
{
ITransaction transaction = Session.BeginTransaction();
try
{
transaction.Commit();
}
catch (HibernateException ex)
{
transaction.Rollback();
//close and dispose session here
throw ex;
}
finally
{
transaction.Dispose();
}
}
Now, if a manual call to flush() or a call to commit() goes through successfully there isn't a way to roll back the transaction using NHibernate mechanisms.
Especially when calling the transaction.Commit() command the AdoTransaction created by NHibernate is then disposed right after the Commit() finishes so you cannot access it in order to roll back.
The code sample above allows you to catch errors that happen during commit and then roll back the transaction that has started already.
Now instead of calling the transaction.Commit() in the sample above you call the session.Flush() in my tests no data are saved in the Database as the transaction is never commited.
I have no idea how your code looks like but if you are calling in a pattern, as the above the code sample shows, the transaction.commit() instead of the Session.Flush() it should give you a way to achieve what you want.