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• Sending emails in web applications

  - by Denise

  Hi everyone, I'm looking for some opinions here, I'm building a web application which has the fairly standard functionality of: Register for an account by filling out a form and submitting it. Receive an email with a confirmation code link Click the link to confirm the new account and log in When you send emails from your web application, it's often (usually) the case that there will be some change to the persistence layer. For example: A new user registers for an account on your site - the new user is created in the database and an email is sent to them with a confirmation link A user assigns a bug or issue to someone else - the issue is updated and email notifications are sent. How you send these emails can be critical to the success of your application. How you send them depends on how important it is that the intended recipient receives the email. We'll look at the following four strategies in relation to the case where the mail server is down, using example 1. TRANSACTIONAL & SYNCHRONOUS The sending of the email fails and the user is shown an error message saying that their account could not be created. The application will appear to be slow and unresponsive as the application waits for the connection timeout. The account is not created in the database because the transaction is rolled back. TRANSACTIONAL & ASYNCHRONOUS The transactional definition here refers to sending the email to a JMS queue or saving it in a database table for another background process to pick up and send. The user account is created in the database, the email is sent to a JMS queue for processing later. The transaction is successful and committed. The user is shown a message saying that their account was created and to check their email for a confirmation link. It's possible in this case that the email is never sent due to some other error, however the user is told that the email has been sent to them. There may be some delay in getting the email sent to the user if application support has to be called in to diagnose the email problem. NON-TRANSACTIONAL & SYNCHRONOUS The user is created in the database, but the application gets a timeout error when it tries to send the email with the confirmation link. The user is shown an error message saying that there was an error. The application is slow and unresponsive as it waits for the connection timeout When the mail server comes back to life and the user tries to register again, they are told their account already exists but has not been confirmed and are given the option of having the email re-sent to them. NON-TRANSACTIONAL & ASYNCHRONOUS The only difference between this and transactional & asynchronous is that if there is an error sending the email to the JMS queue or saving it in the database, the user account is still created but the email is never sent until the user attempts to register again. What I'd like to know is what have other people done here? Can you recommend any other solutions other than the 4 I've mentioned above? What's a reasonable way of approaching this problem? I don't want to over-engineer a system that's dealing with the (hopefully) rare situation where my mail server goes down! The simplest thing to do is to code it synchronously, but are there any other pitfalls to this approach? I guess I'm wondering if there's a best practice, I couldn't find much out there by googling.

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• Question about spring transaction propagation

  - by Yousui

  Hi guys, I have a question about spring transaction propagation. If I use @Transactional(propagation = Propagation.REQUIRED) to annotate a method m1. When execution logic enter m1, if there is already a transaction, m1 will use that one. When after m1, what about the transaction? It ends or still open?(if I call m1 in another method, and after the invocation there is still other things to do). In summary, I want to know when exiting an annotated method, the transaction ends or still open? Great thanks.

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• Hibernate save() and transaction rollback

  - by Marco

  Hi, In Hibernate when i save() an object in a transaction, and then i rollback it, the saved object still remains in the DB. It's strange because this issue doesn't happen with the update() or delete() method, just with save(). Here is the code i'm using: DbEntity dbEntity = getDbEntity(); HibernateUtil.beginTransaction(); Session session = HibernateUtil.getCurrentSession(); session.save(dbEntity); HibernateUtil.rollbackTransaction(); And here is the HibernateUtil class (just the involved functions, i guarantee the getSessionFactory() method works well - there is an Interceptor handler, but it doesn't matter now): private static final ThreadLocal<Session> threadSession = new ThreadLocal<Session>(); private static final ThreadLocal<Transaction> threadTransaction = new ThreadLocal<Transaction>(); /** * Retrieves the current Session local to the thread. * <p/> * If no Session is open, opens a new Session for the running thread. * * @return Session */ public static Session getCurrentSession() throws HibernateException { Session s = (Session) threadSession.get(); try { if (s == null) { log.debug("Opening new Session for this thread."); if (getInterceptor() != null) { log.debug("Using interceptor: " + getInterceptor().getClass()); s = getSessionFactory().openSession(getInterceptor()); } else { s = getSessionFactory().openSession(); } threadSession.set(s); } } catch (HibernateException ex) { throw new HibernateException(ex); } return s; } /** * Start a new database transaction. */ public static void beginTransaction() throws HibernateException { Transaction tx = (Transaction) threadTransaction.get(); try { if (tx == null) { log.debug("Starting new database transaction in this thread."); tx = getCurrentSession().beginTransaction(); threadTransaction.set(tx); } } catch (HibernateException ex) { throw new HibernateException(ex); } } /** * Rollback the database transaction. */ public static void rollbackTransaction() throws HibernateException { Transaction tx = (Transaction) threadTransaction.get(); try { threadTransaction.set(null); if ( tx != null && !tx.wasCommitted() && !tx.wasRolledBack() ) { log.debug("Tyring to rollback database transaction of this thread."); tx.rollback(); } } catch (HibernateException ex) { throw new HibernateException(ex); } finally { closeSession(); } } Thanks

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• TSQL: comma combination, transaction?

  - by deerchao

  Are these 2 statements below run in an implicit transaction? select * from a; select * from b;

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• ADO.NET zombie transaction bug? How to ensure that commands will not be executed on implicit transac

  - by TN

  e.g. When deadlock occurs, following SQL commands are successfully executed, even if they have assigned SQL transaction that is after rollback. It seems, it is caused by a new implicit transaction that is created on SQL Server. Someone could expect that ADO.NET would throw an exception that the commands are being executed on a zombie transaction. However, such exception is not thrown. (I think this is a bug in ASP.NET.) Moreover, because of zombie transaction the final Dispose() silently ignores the rollback. Any ideas, how can I ensure that nobody can execute commands on implicit transaction? Or, how to check that transaction is zombie? I found that Commit() and Rollback() check for zombie transaction, however I can call them for a test:) I also found that also reading IsolationLevel will do the check, but I am not sure whether simple calling transaction.IsolationLevel.ToString(); will not be removed by a future optimizer. Or do you know any other safe way invoke a getter (without using reflection or IL emitting)?

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• Can I use TransactionScope to do distributed transaction?

  - by Malcolm

  Hi I have a MVC app that use Linq2Sql to access a SQL DB. But I want create a distributed transaction to update another DB on different local server. Can I just wrap logic in TransactionScope class??? Malcolm

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• Is it bad practice to extend the MongoEngine User document?

  - by Soviut

  I'm integrating MongoDB using MongoEngine. It provides auth and session support that a standard pymongo setup would lack. In regular django auth, it's considered bad practice to extend the User model since there's no guarantee it will be used correctly everywhere. Is this the case with mongoengine.django.auth? If it is considered bad practice, what is the best way to attach a separate user profile? Django has mechanisms for specifying an AUTH_PROFILE_MODULE. Is this supported in MongoEngine as well, or should I be manually doing the lookup?

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• IDbTransaction Rollback Timeout

  - by Ben

  I am dealing with an interesting situation where I perform many database updates in a single transaction. If these updates fail for any reason, the transaction is rolled-back. IDbTransaction transaction try { transaction = connection.BeginTransaction(); // do lots of updates (where at least one fails) transaction.Commit(); } catch { transaction.Rollback(); // results in a timeout exception } finally { connection.Dispose(); } I believe the above code is generally considered the standard template for performing database updates within a transaction. The issue I am facing is that whilst transaction.Rollback() is being issued to SQL Server, it is also timing out on the client. Is there anyway of distinguishing between a timeout to issue the rollback command and a timeout on that command executing to completion? Thanks in advance, Ben

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• At what line in the following code should I be commiting my UnitOfWork ?

  - by Pure.Krome

  Hi folks, I have the following code which is in a transaction. I'm not sure where/when i should be commiting my unit of work. If someone knows where, can they please explain WHY they have said, where? (i'm trying to understand the pattern through example(s), as opposed to just getting my code to work). Here's what i've got :- using (TransactionScope transactionScope = new TransactionScope(TransactionScopeOption.RequiresNew, new TransactionOptions { IsolationLevel = IsolationLevel.ReadUncommitted })) { _logEntryRepository.InsertOrUpdate(logEntry); //_unitOfWork.Commit(); // Here, commit #1 ? // Now, if this log entry was a NewConnection or an LostConnection, then we need to make sure we update the ConnectedClients. if (logEntry.EventType == EventType.NewConnection) { _connectedClientRepository.Insert(new ConnectedClient { LogEntryId = logEntry.LogEntryId }); //_unitOfWork.Commit(); // Here, commit #2 ? } // A (PB) BanKick does _NOT_ register a lost connection .. so we need to make sure we handle those scenario's as a LostConnection. if (logEntry.EventType == EventType.LostConnection || logEntry.EventType == EventType.BanKick) { _connectedClientRepository.Delete(logEntry.ClientName, logEntry.ClientIpAndPort); //_unitOfWork.Commit(); // Here, commit #3 ? } _unitOfWork.Commit(); // Here, commit #4 ? transactionScope.Complete(); } Cheers :)

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• Why do System.IO.Log SequenceNumbers have variable length?

  - by Doug McClean

  I'm trying to use the System.IO.Log features to build a recoverable transaction system. I understand it to be implemented on top of the Common Log File System. The usual ARIES approach to write-ahead logging involves persisting log record sequence numbers in places other than the log (for example, in the header of the database page modified by the logged action). Interestingly, the documentation for CLFS says that such sequence numbers are always 64-bit integers. Confusingly, however, the .Net wrapper around those SequenceNumbers can be constructed from a byte[] but not from a UInt64. It's value can also be read as a byte[], but not as a UInt64. Inspecting the implementation of SequenceNumber.GetBytes() reveals that it can in fact return arrays of either 8 or 16 bytes. This raises a few questions: Why do the .Net sequence numbers differ in size from the CLFS sequence numbers? Why are the .Net sequence numbers variable in length? Why would you need 128 bits to represent such a sequence number? It seems like you would truncate the log well before using up a 64-bit address space (16 exbibytes, or around 10^19 bytes, more if you address longer words)? If log sequence numbers are going to be represented as 128 bit integers, why not provide a way to serialize/deserialize them as pairs of UInt64s instead of rather-pointlessly incurring heap allocations for short-lived new byte[]s every time you need to write/read one? Alternatively, why bother making SequenceNumber a value type at all? It seems an odd tradeoff to double the storage overhead of log sequence numbers just so you can have an untruncated log longer than a million terabytes, so I feel like I'm missing something here, or maybe several things. I'd much appreciate it if someone in the know could set me straight.

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• Having a destructor take different actions depending on whether an exception occurred

  - by dan04

  I have some code to update a database table that looks like try { db.execute("BEGIN"); // Lots of DELETE and INSERT db.execute("COMMIT"); } catch (DBException&) { db.execute("ROLLBACK"); } I'd like to wrap the transaction logic in an RAII class so I could just write { DBTransaction trans(db); // Lots of DELETE and INSERT } but how would I write the destructor for it?

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• How do these user/userParam references relate to the Customer and Account lookups?

  - by marmalade

  In the following code example how do the user/userParam references relate to the Customer and Account lookups and what is the relationship between Customer and Account? // PersistenceManager pm = ...; Transaction tx = pm.currentTransaction(); User user = userService.currentUser(); List<Account> accounts = new ArrayList<Account>(); try { tx.begin(); Query query = pm.newQuery("select from Customer " + "where user == userParam " + "parameters User userParam"); List<Customer> customers = (List<Customer>) query.execute(user); query = pm.newQuery("select from Account " + "where parent-pk == keyParam " + "parameters Key keyParam"); for (Customer customer : customers) { accounts.addAll((List<Account>) query.execute(customer.key)); } } finally { if (tx.isActive()) { tx.rollback(); } }

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• How do these user/userParam references relate to the Customer and Account lookups?

  - by plath

  In the following code example how do the user/userParam references relate to the Customer and Account lookups and what is the relationship between Customer and Account? // PersistenceManager pm = ...; Transaction tx = pm.currentTransaction(); User user = userService.currentUser(); List<Account> accounts = new ArrayList<Account>(); try { tx.begin(); Query query = pm.newQuery("select from Customer " + "where user == userParam " + "parameters User userParam"); List<Customer> customers = (List<Customer>) query.execute(user); query = pm.newQuery("select from Account " + "where parent-pk == keyParam " + "parameters Key keyParam"); for (Customer customer : customers) { accounts.addAll((List<Account>) query.execute(customer.key)); } } finally { if (tx.isActive()) { tx.rollback(); } }

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• Does a transaction stop all race condition problems in MySQL?

  - by nickf

  Consider this situation: Begin transaction Insert 20 records into a table with an auto_increment key Get the first insert id (let's say it's 153) Update all records in that table where id >= 153 Commit Is step 4 safe? That is, if another request comes in almost precisely at the same time, and inserts another 20 records after step 2 above, but before step 4, will there be a race condition?

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• Can I get a reference to a pending transaction from a SqlConnection object?

  - by Rune

  Hey, Suppose someone (other than me) writes the following code and compiles it into an assembly: using (SqlConnection conn = new SqlConnection(connString)) { conn.Open(); using (var transaction = conn.BeginTransaction()) { /* Update something in the database */ /* Then call any registered OnUpdate handlers */ InvokeOnUpdate(conn); transaction.Commit(); } } The call to InvokeOnUpdate(IDbConnection conn) calls out to an event handler that I can implement and register. Thus, in this handler I will have a reference to the IDbConnection object, but I won't have a reference to the pending transaction. Is there any way in which I can get a hold of the transaction? In my OnUpdate handler I want to execute something similar to the following: private void MyOnUpdateHandler(IDbConnection conn) { var cmd = conn.CreateCommand(); cmd.CommandText = someSQLString; cmd.CommandType = CommandType.Text; cmd.ExecuteNonQuery(); } However, the call to cmd.ExecuteNonQuery() throws an InvalidOperationException complaining that "ExecuteNonQuery requires the command to have a transaction when the connection assigned to the command is in a pending local transaction. The Transaction property of the command has not been initialized". Can I in any way enlist my SqlCommand cmd with the pending transaction? Can I retrieve a reference to the pending transaction from the IDbConnection object (I'd be happy to use reflection if necessary)?

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• mysql innodb max size of transaction

  - by chris

  Using mysql 5.1.41 and innodb I'm doing some data import, but can't use load data infile, so I'm manually issuing insert statements. I found that it's much faster to disable auto commit and issue say, 100 insert statements and then commit, instead of the implicit commit after each insert. It got me thinking, what limits are there to how much data I can put into a transaction? Is there a limit on the number of statements, or does it have to do with the size in bytes etc...?

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• How to move an element in a sorted list and keep the CouchDb write "atomic"

  - by karlthorwald

  I have elements of a list in couchdb documents. Let's say these are 3 elements in 3 documents: { "id" : "783587346", "type" : "aList", "content" : "joey", "sort" : 100.0 } { "id" : "358734ff6", "type" : "aList", "content" : "jill", "sort" : 110.0 } { "id" : "abf587346", "type" : "aList", "content" : "jack", "sort" : 120.0 } A view retrieves all "aList" documents and displays them sorted by "sort". Now I want to move the elements, when I want to move "jack" to the middle, I could do this atomic in one write and change it's sort key to 105.0. The view now returns the documents in the new sort order. After a lot of sorting I could end up with sort keys like 50.99999 and 50.99998 after some years and in extreme situations run out of digits? What can you recommend, is there a better way to do this? I'd rather keep the elements in seperate documents. Different users might edit different elements in parallel (which also can get tricky). Maybe there is a much better way?

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• In MS SQL Server, is there a way to "atomically" increment a column being used as a counter?

  - by Dan P

  Assuming a Read Committed Snapshot transaction isolation setting, is the following statement "atomic" in the sense that you won't ever "lose" a concurrent increment? update mytable set counter = counter + 1 I would assume that in the general case, where this update statement is part of a larger transaction, that it wouldn't be. For example, I think this scenario is possible: update the counter within transaction #1 do some other stuff in transaction #1 update the counter with transaction #2 commit transaction #2 commit transaction #1 In this situation, wouldn't the counter end up only being incremented by 1? Does it make a difference if that is the only statement in a transaction? How does a site like stackoverflow handle this for its question view counter? Or is the possibility of "losing" some increments just considered acceptable?

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• INSERT and transaction serialization in PostreSQL

  - by Alexander

  I have a question. Transaction isolation level is set to serializable. When the one user opens a transaction and INSERTs or UPDATEs data in "table1" and then another user opens a transaction and tries to INSERT data to the same table, does the second user need to wait 'til the first user commits the transaction?

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• Can we ask user for credit card number or paypal details,store credit card number on our server, can

  - by Hiren Gujarati

  Can we get credit card number from user or paypal details & use them for premium service of our application ? is apple accept this application if we directly get this information & use it in our api on server for transaction. Using ssl will be accpted by apple ? I have check from 1) http://stackoverflow.com/questions/1763306/credit-card-purchase-of-physical-goods-via-an-iphone-application 2) http://stackoverflow.com/questions/1707701/receiving-payments-trough-paypal-and-credit-card 3) http://stackoverflow.com/questions/1366864/using-the-paypal-api-in-an-iphone-application but not clear about all...

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• How do I get save (no exclamation point) semantics in an ActiveRecord transaction?

  - by James A. Rosen

  I have two models: Person and Address which I'd like to create in a transaction. That is, I want to try to create the Person and, if that succeeds, create the related Address. I would like to use save semantics (return true or false) rather than save! semantics (raise an ActiveRecord::StatementInvalid or not). This doesn't work because the user.save doesn't trigger a rollback on the transaction: class Person def save_with_address(address_options = {}) transaction do self.save address = Address.build(address_options) address.person = self address.save end end end (Changing the self.save call to an if self.save block around the rest doesn't help, because the Person save still succeeds even when the Address one fails.) And this doesn't work because it raises the ActiveRecord::StatementInvalid exception out of the transaction block without triggering an ActiveRecord::Rollback: class Person def save_with_address(address_options = {}) transaction do save! address = Address.build(address_options) address.person = self address.save! end end end The Rails documentation specifically warns against catching the ActiveRecord::StatementInvalid inside the transaction block. I guess my first question is: why isn't this transaction block... transacting on both saves?

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• Why is TransactionScope using a distributed transaction when I am only using LinqToSql and Ado.Net

  - by Ian Ringrose

  We are having problems on one machine, with the error message: "MSDTC on server XXX is unavailable." The code is using a TransactionScope to wrap some LingToSql database code; there is also some raw Ado.net inside of the transaction. As only a single sql database (2005) is being accessed, why is a distributed transaction being used at all? (I don’t wish to know how to enable MSDTC, as the code needs to work on the server with their current setup)

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• Rails ActiveRecord Transaction does not finish

  - by PanosJee

  Hi everyone, I have a Transaction for a batch insert/update block and all of sudden it stopped working. The are no errors or exception risen and it seems like Rails stops just before the end of the Transaction blog so the methods does not return. I restarted both MySQL and the system but still.

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• Reading from a oracle temp table in a separate procedure than the one it was populted in

  - by Bob

  I have a 2 stored procedures, the first creates an oracle temp table and the second reads from it. The temp table only has scope for that session. I'm calling the procedures from .Net and the second procedure never returns any results. However if I use the same sprocs and parameters in SQL*Plus it works fine. I've tried creating an Oracle Transaction object and had hoped I'd be able to read the tables in while still using the same transaction - trying to emulate an SQL Plus type of single connection environment. Any ideas what I'm doing wrong??

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• What does this do and why does it require a transaction?

  - by S. Palin

  What does the following code example do and why does it require a transaction? // PersistenceManager pm = ...; Transaction tx = pm.currentTransaction(); User user = userService.currentUser(); List<Account> accounts = new ArrayList<Account>(); try { tx.begin(); Query query = pm.newQuery("select from Customer " + "where user == userParam " + "parameters User userParam"); List<Customer> customers = (List<Customer>) query.execute(user); query = pm.newQuery("select from Account " + "where parent-pk == keyParam " + "parameters Key keyParam"); for (Customer customer : customers) { accounts.addAll((List<Account>) query.execute(customer.key)); } } finally { if (tx.isActive()) { tx.rollback(); } }

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