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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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  • 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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  • 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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  • 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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  • Grouping data in an NSMutable array

    - by padatronic
    Hi guys, I have an array i load with lots of data from an xml file. I am displaying this on a tableview and then when you click on say an author it goes through to display all their books. At the minute my NSMutableArray has an entry for every each book with title, author and so on. So in the table of authors it display the authors name as many times as they have books. I want to group the array data so the table only displays each author once but the author contains an array of his books. Seems simple but I can't find a group method for arrays. thanks peeps

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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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  • 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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  • 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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  • 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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  • Transactional isolation level needed for safely incrementing ids

    - by Knut Arne Vedaa
    I'm writing a small piece of software that is to insert records into a database used by a commercial application. The unique primary keys (ids) in the relevant table(s) are sequential, but does not seem to be set to "auto increment". Thus, I assume, I will have to find the largest id, increment it and use that value for the record I'm inserting. In pseudo-code for brevity: id = select max(id) from some_table id++ insert into some_table values(id, othervalues...) Now, if another thread started the same transaction before the first one finished its insert, you would get two identical ids and a failure when trying to insert the last one. You could check for that failure and retry, but a simpler solution might be setting an isolation level on the transaction. For this, would I need SERIALIZABLE or a lower level? Additionally, is this, generally, a sound way of solving the problem? Are the any other ways of doing it?

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  • ASP.NET, C#: timeout when trying to Transaction.Commit() to database; potential deadlock?

    - by user1843921
    I have a web page that has coding structured somewhat as follows: SqlConnection conX =new SqlConnection(blablabla); conX.Open(); SqlTransaction tran=conX.BeginTransaction(); try{ SqlCommand cmdInsert =new SqlCommand("INSERT INTO Table1(ColX,ColY) VALUES @x,@y",conX); cmdInsert.Transaction=tran; cmdInsert.ExecuteNonQuery(); SqlCommand cmdSelect=new SqlCOmmand("SELECT * FROM Table1",conX); cmdSelect.Transaction=tran; SqlDataReader dtr=cmdSelect.ExecuteReader(); //read stuff from dtr dtr.Close(); cmdInsert=new SqlCommand("UPDATE Table2 set ColA=@a",conX); cmdInsert.Transaction=tran; cmdInsert.ExecuteNonQuery(); //display MiscMessage tran.Commit(); //display SuccessMessage } catch(Exception x) { tran.Rollback(); //display x.Message } finally { conX.Close(); } So, everything seems to work until MiscMessage. Then, after a while (maybe 15-ish seconds?) x.Message pops up, saying that: "Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding." So something wrong with my trans.Commit()? The database is not updated so I assume the trans.Rollback works... I have read that deadlocks can cause timeouts...is this problem cause by my SELECT statement selecting from Table1, which is being used by the first INSERT statement? If so, what should I do? If that ain't the problem, what is?

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  • Are concurrency issues possible when using the WCF Service Behavoir attribute set to ConcurrencyMode

    - by Brandon Linton
    We have a WCF service that makes a good deal of transactional NHibernate calls. Occasionally we were seeing SQL timeouts, even though the calls were updating different rows and the tables were set to row level locking. After digging into the logs, it looks like different threads were entering the same point in the code (our transaction using block), and an update was hanging on commit. It didn't make sense, though, because we believed that the following service class attribute was forcing a unique execution thread per service call: [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Multiple, InstanceContextMode = InstanceContextMode.PerCall)] We recently changed the concurrency mode to ConcurrencyMode.Single and haven't yet run into any issues, but the bug was very difficult to reproduce (if anyone has any thoughts on flushing a bug like that out, let me know!). Anyway, that all brings me to my question: shouldn't an InstanceContextMode of PerCall enforce thread-safety within the service, even if the ConcurrencyMode is set to multiple? How would it be possible for two calls to be serviced by the same service instance? Thanks!

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  • Hos to group the complex list objects by using Linq

    - by Daoming Yang
    I want to select and group the products, and rank them by the number of times they occur. For example, I have an OrderList each of order object has a OrderProductVariantList(OrderLineList), and each of OrderProductVariant object has ProductVariant, and then the ProductVariant object will have a Product object which contains product information. A friend helped me with the following code. It could be compiled, but it did not return any value/result. I used the watch window for the query and it gave me "The name 'query' does not exist in the current context". Can anyone help me? Many thanks. var query = orderList.SelectMany( o => o.OrderLineList ) // results in IEnumerable<OrderProductVariant> .Select( opv => opv.ProductVariant ) .Select( pv => p.Product ) .GroupBy( p => p ) .Select( g => new { Product = g.Key, Count = g.Count() });

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  • Transaction issue in java with hibernate - latest entries not pulled from database

    - by Gearóid
    Hi, I'm having what seems to be a transactional issue in my application. I'm using Java 1.6 and Hibernate 3.2.5. My application runs a monthly process where it creates billing entries for a every user in the database based on their monthly activity. These billing entries are then used to create Monthly Bill object. The process is: Get users who have activity in the past month Create the relevant billing entries for each user Get the set of billing entries that we've just created Create a Monthly Bill based on these entries Everything works fine until Step 3 above. The Billing Entries are correctly created (I can see them in the database if I add a breakpoint after the Billing Entry creation method), but they are not pulled out of the database. As a result, an incorrect Monthly Bill is generated. If I run the code again (without clearing out the database), new Billing Entries are created and Step 3 pulls out the entries created in the first run (but not the second run). This, to me, is very confusing. My code looks like the following: for (User user : usersWithActivities) { createBillingEntriesForUser(user.getId()); userBillingEntries = getLastMonthsBillingEntriesForUser(user.getId()); createXMLBillForUser(user.getId(), userBillingEntries); } The methods called look like the following: @Transactional public void createBillingEntriesForUser(Long id) { UserManager userManager = ManagerFactory.getUserManager(); User user = userManager.getUser(id); List<AccountEvent> events = getLastMonthsAccountEventsForUser(id); BillingEntry entry = new BillingEntry(); if (null != events) { for (AccountEvent event : events) { if (event.getEventType().equals(EventType.ENABLE)) { Calendar cal = Calendar.getInstance(); Date eventDate = event.getTimestamp(); cal.setTime(eventDate); double startDate = cal.get(Calendar.DATE); double numOfDaysInMonth = cal.getActualMaximum(Calendar.DAY_OF_MONTH); double numberOfDaysInUse = numOfDaysInMonth - startDate; double fractionToCharge = numberOfDaysInUse/numOfDaysInMonth; BigDecimal amount = BigDecimal.valueOf(fractionToCharge * Prices.MONTHLY_COST); amount.scale(); entry.setAmount(amount); entry.setUser(user); entry.setTimestamp(eventDate); userManager.saveOrUpdate(entry); } } } } @Transactional public Collection<BillingEntry> getLastMonthsBillingEntriesForUser(Long id) { if (log.isDebugEnabled()) log.debug("Getting all the billing entries for last month for user with ID " + id); //String queryString = "select billingEntry from BillingEntry as billingEntry where billingEntry>=:firstOfLastMonth and billingEntry.timestamp<:firstOfCurrentMonth and billingEntry.user=:user"; String queryString = "select be from BillingEntry as be join be.user as user where user.id=:id and be.timestamp>=:firstOfLastMonth and be.timestamp<:firstOfCurrentMonth"; //This parameter will be the start of the last month ie. start of billing cycle SearchParameter firstOfLastMonth = new SearchParameter(); firstOfLastMonth.setTemporalType(TemporalType.DATE); //this parameter holds the start of the CURRENT month - ie. end of billing cycle SearchParameter firstOfCurrentMonth = new SearchParameter(); firstOfCurrentMonth.setTemporalType(TemporalType.DATE); Query query = super.entityManager.createQuery(queryString); query.setParameter("firstOfCurrentMonth", getFirstOfCurrentMonth()); query.setParameter("firstOfLastMonth", getFirstOfLastMonth()); query.setParameter("id", id); List<BillingEntry> entries = query.getResultList(); return entries; } public MonthlyBill createXMLBillForUser(Long id, Collection<BillingEntry> billingEntries) { BillingHistoryManager manager = ManagerFactory.getBillingHistoryManager(); UserManager userManager = ManagerFactory.getUserManager(); MonthlyBill mb = new MonthlyBill(); User user = userManager.getUser(id); mb.setUser(user); mb.setTimestamp(new Date()); Set<BillingEntry> entries = new HashSet<BillingEntry>(); entries.addAll(billingEntries); String xml = createXmlForMonthlyBill(user, entries); mb.setXmlBill(xml); mb.setBillingEntries(entries); MonthlyBill bill = (MonthlyBill) manager.saveOrUpdate(mb); return bill; } Help with this issue would be greatly appreciated as its been wracking my brain for weeks now! Thanks in advance, Gearoid.

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  • Oracle transaction read-consistency ?

    - by trojanwarrior3000
    I have problem understanding read consistency in db(oracle). Suppose I am manger of a bank . A customer has got lock (which I dont know) and is doing some updation. Now after he has got lock I am viewing account info of the same customer and try to do some thing on it.But because of read consistency I will see data as it existed before customer got the lock. So will not that affect inputs I am getting and the decisions that I am gonna make during that period?

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  • What does really happen when we do a BEGIN TRAN in SQL Server 2005?

    - by Misnomer
    Hi all, I came across this issue or maybe something I didn't realize but I did a Begin Tran and had some code inside it and never ran a commit or rollback as I forgot about it. That caused all many of the database queries or even just a simple select top 1000 command were just sitting on loading..? Now it probably has put some locks on the tables I guess since it did not let me query them..but I just wanted to know what exactly happened and what are the practices to be followed here ?

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