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• Building "isolated" and "automatically updated" caches (java.util.List) in Java.

  - by Aidos

  Hi Guys, I am trying to write a framework which contains a lot of short-lived caches created from a long-living cache. These short-lived caches need to be able to return their entier contents, which is a clone from the original long-living cache. Effectively what I am trying to build is a level of transaction isolation for the short-lived caches. The user should be able to modify the contents of the short-lived cache, but changes to the long-living cache should not be propogated through (there is also a case where the changes should be pushed through, depending on the Cache type). I will do my best to try and explain: master-cache contains: [A,B,C,D,E,F] temporary-cache created with state [A,B,C,D,E,F] 1) temporary-cache adds item G: [A,B,C,D,E,F] 2) temporary-cache removes item B: [A,C,D,E,F] master-cache contains: [A,B,C,D,E,F] 3) master-cache adds items [X,Y,Z]: [A,B,C,D,E,F,X,Y,Z] temporary-cache contains: [A,C,D,E,F] Things get even harder when the values in the items can change and shouldn't always be updated (so I can't even share the underlying object instances, I need to use clones). I have implemented the simple approach of just creating a new instance of the List using the standard Collection constructor on ArrayList, however when you get out to about 200,000 items the system just runs out of memory. I know the value of 200,000 is excessive to iterate, but I am trying to stress my code a bit. I had thought that it might be able to somehow "proxy" the list, so the temporary-cache uses the master-cache, and stores all of it's changes (effectively a Memento for the change), however that quickly becomes a nightmare when you want to iterate the temporary-cache, or retrieve an item at a specific index. Also given that I want some modifications to the contents of the list to come through (depending on the type of the temporary-cache, whether it is "auto-update" or not) and I get completly out of my depth. Any pointers to techniques or data-structures or just general concepts to try and research will be greatly appreciated. Cheers, Aidos

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• INSERT and transaction searilization in PostreSQL

  - by Alexander

  Hello! I have a question. Transaction isolation level set to serializable. When the one user open transaction and INSERT or UPDATE data in "table1" and then another user open transaction and try to INSERT data to the same table is second user need to wait 'til the first user commits the transaction?

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• JTA Transaction: What happens if an exception happens but rollback is not called on the transaction?

  - by kellyfj

  We have some third party code wherein they do the following 1) Create a User Transaction e.g. txn = (UserTransaction)ctx.lookup( "UserTransaction" ); txn.begin( ); 2) Do some work persisting to the database (via JPA) to a MySQL database 3) txn.commit() They have Exception blocks but NONE of them call txn.rollback. Good coding practice says they NEED to call rollback if an exception occurs but my question is If the txn is not commited, and an exception occurs what is the negative effect of them NOT calling rollback?

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• Data access strategy for a site like SO - sorted SQL queries and simultaneous updates that affect th

  - by Kaleb Brasee

  I'm working on a Grails web app that would be similar in access patterns to StackOverflow or MyLifeIsAverage - users can vote on entries, and their votes are used to sort a list of entries based on the number of votes. Votes can be placed while the sorted select queries are being performed. Since the selects would lock a large portion of the table, it seems that normal transaction locking would cause updates to take forever (given enough traffic). Has anyone worked on an app with a data access pattern such as this, and if so, did you find a way to allow these updates and selects to happen more or less concurrently? Does anyone know how sites like SO approach this? My thought was to make the sorted selects dirty reads, since it is acceptable if they're not completely up to date all of the time. This is my only idea for possibly improving performance of these selects and updates, but I thought someone might know a better way.

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• Problem getting value from "Checkbox group value prompt"

  - by Veer

  Hi, I've value prompt with ui:checkbox group parameter: p_IsLastMonth Name: Prompt_IsLastMonth ItemCount: 1; UseValue:Yes, DisplayValue: LastMonth? and two Date Prompts. Whenever the checkbox is checked, the UseValue 'Yes' is passed to the parameter 'p_IsLastMonth'. But whenever the checkbox is left as it is, it results in an error. Element 'selectOptions' is not valid for content model: 'All(style,defaultSelections,conditionalStyles,conditionalRender,XMLAttributes)' I also tried giving a default value. But the default value has to be in the collection. But i want only one checkbox to be displayed. I tried with html checkbox. But i'm not able to send the value 'either yes or no' to the parameter through javascript because however the finish button overrides the value. Any help?

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• Best practice for web server user/group permissions

  - by Poe

  What's the best practice in a secure manner to setup the user/group and permissions? Here's what we currently have; web server runs as www/www. Fastcgi Php runs as www/www. User's shell/ftp account is username/username. We want the user to be able to have full access to all files, including those created by the web server 'www' from the shell or ftp. Similarly, we want the scripts run by fastcgi/php to be able to create files in user created directories and modify user created files.

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• Translate HTML files to another language

  - by Saif Bechan

  I have a website with Dutch text which I want to translate to English. Is there a fast way of doing this with keeping the HTML tags(<strong>,<span>) in tact. I know I can just copy the parsed TEXT into a translator but this will remove the formatting. I also know that at the end I have to go trough the text manually to fix some minor spelling and grammar.

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• A simple group-by (no count) in Django

  - by Daniel Quinn

  If this were raw-SQL, it'd be a no-brainer, but in Django, this is proving to be quite difficult to find. What I want is this really: SELECT user_id FROM django_comments WHERE content_type_id = ? AND object_pk = ? GROUP BY user_id It's those last two lines that're the problem. I'd like to do this the "Django-way" but the only thing I've found is mention of aggregates and annotations, which I don't think solve this issue... do they? If someone could explain this to me, I'd really appreciate it.

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• Insert takes too long, code optimization needed

  - by Pentium10

  I have some code I use to transfer a table1 values to another table2, they are sitting in different database. It's slow when I have 100.000 records. It takes forever to finish, 10+ minutes. (Windows Mobile smartphone) What can I do? cmd.CommandText = "insert into " + TableName + " select * from sync2." + TableName+""; cmd.ExecuteNonQuery(); EDIT The problem is not resolved. I am still after answers.

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• access custom group

  - by Carlos

  I have my Access 2007 database configured to use "Custom" groups in the navigation pane. I've grouped all my tables in a way that makes sense. However, whenever I update a link table, it loses its grouping. I have not been able to find a way to avoid this. Since it seems to be unavoidable, I'd like to simply have a macro that adds the table back to the right group programatically. I have not found any examples on how to do this. Any suggestions?

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• How do i set Savepoints for Linq to SQL and use "NO" ExecuteCommand ?

  - by nik

  TransactionScope TransactionABC = new TransactionScope(); try { context.Connection.Open(); { context.ExecuteCommand("insert into test (test) values (1)") context.SubmitChanges(); context.ExecuteCommand("savepoint test"); context.ExecuteCommand("insert into test (test) values (2)") context.SubmitChanges(); context.ExecuteCommand("rollback to test"); } TransactionABC.Complete(); TransactionABC.Dispose(); } catch (Exception ec) { MessageBox.Show(" ", ec.Message); } finally { context.Connection.Close(); } It works, but only with ExecuteCommand. I want to use a function, because i can't see what happens in the savepoint !

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• Unit Testing the Use of TransactionScope

  - by Randolpho

  The preamble: I have designed a strongly interfaced and fully mockable data layer class that expects the business layer to create a TransactionScope when multiple calls should be included in a single transaction. The problem: I would like to unit test that my business layer makes use of a TransactionScope object when I expect it to. Unfortunately, the standard pattern for using TransactionScope is a follows: using(var scope = new TransactionScope()) { // transactional methods datalayer.InsertFoo(); datalayer.InsertBar(); scope.Complete(); } While this is a really great pattern in terms of usability for the programmer, testing that it's done seems... unpossible to me. I cannot detect that a transient object has been instantiated, let alone mock it to determine that a method was called on it. Yet my goal for coverage implies that I must. The Question: How can I go about building unit tests that ensure TransactionScope is used appropriately according to the standard pattern? Final Thoughts: I've considered a solution that would certainly provide the coverage I need, but have rejected it as overly complex and not conforming to the standard TransactionScope pattern. It involves adding a CreateTransactionScope method on my data layer object that returns an instance of TransactionScope. But because TransactionScope contains constructor logic and non-virtual methods and is therefore difficult if not impossible to mock, CreateTransactionScope would return an instance of DataLayerTransactionScope which would be a mockable facade into TransactionScope. While this might do the job it's complex and I would prefer to use the standard pattern. Is there a better way?

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• SQLAlchemy autocommiting?

  - by muckabout

  I have an issue with SQLAlchemy apparently committing. A rough sketch of my code: trans = self.conn.begin() try: assert not self.conn.execute(my_obj.__table__.select(my_obj.id == id)).first() self.conn.execute(my_obj.__table__.insert().values(id=id)) assert not self.conn.execute(my_obj.__table__.select(my_obj.id == id)).first() except: trans.rollback() raise I don't commit, and the second assert always fails! In other words, it seems the data is getting inserted into the database even though the code is within a transaction! Is this assessment accurate?

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• MySQL Query Join Table Selecting Highest Date Value

  - by ALHUI

  Here is the query that I run SELECT cl.cl_id, cc_rego, cc_model, cl_dateIn, cl_dateOut FROM courtesycar cc LEFT JOIN courtesyloan cl ON cc.cc_id = cl.cc_id Results: 1 NXI955 Prado 2013-10-24 11:48:38 NULL 2 RJI603 Avalon 2013-10-24 11:48:42 2013-10-24 11:54:18 3 RJI603 Avalon 2013-10-24 12:01:40 NULL The results that I wanted are to group by the cc_rego values and print the most recent cl_dateIn value. (Only Display Rows 1,3) Ive tried to use MAX on the date and group by clause, but it combines rows, 2 & 3 together showing both the highest value of dateIn and dateOut. Any help will be appreciated.

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• Access DB Transaction on insert or updating

  - by Raju Gujarati

  I am going to implement the database access layer of the Window application using C#. The database (.accdb) is located to the project files. When it comes to two notebooks (clients) connecting to one access database through switches, it throws DBConcurrency Exception Error. My target is to check the timestamp of the sql executed first and then run the sql . Would you please provide me some guidelines to achieve this ? The below is my code protected void btnTransaction_Click(object sender, EventArgs e) { string custID = txtID.Text; string CompName = txtCompany.Text; string contact = txtContact.Text; string city = txtCity.Text; string connString = ConfigurationManager.ConnectionStrings["CustomersDatabase"].ConnectionString; OleDbConnection connection = new OleDbConnection(connString); connection.Open(); OleDbCommand command = new OleDbCommand(); command.Connection = connection; OleDbTransaction transaction = connection.BeginTransaction(); command.Transaction = transaction; try { command.CommandText = "INSERT INTO Customers(CustomerID, CompanyName, ContactName, City, Country) VALUES(@CustomerID, @CompanyName, @ContactName, @City, @Country)"; command.CommandType = CommandType.Text; command.Parameters.AddWithValue("@CustomerID", custID); command.Parameters.AddWithValue("@CompanyName", CompName); command.Parameters.AddWithValue("@ContactName", contact); command.Parameters.AddWithValue("@City", city); command.ExecuteNonQuery(); command.CommandText = "UPDATE Customers SET ContactName = @ContactName2 WHERE CustomerID = @CustomerID2"; command.CommandType = CommandType.Text; command.Parameters.AddWithValue("@CustomerID2", custIDUpdate); command.Parameters.AddWithValue("@ContactName2", contactUpdate); command.ExecuteNonQuery(); adapter.Fill(table); GridView1.DataSource = table; GridView1.DataBind(); transaction.Commit(); lblMessage.Text = "Transaction successfully completed"; } catch (Exception ex) { transaction.Rollback(); lblMessage.Text = "Transaction is not completed"; } finally { connection.Close(); } }

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• Is there any difference in which order I createCriteria and beginTransaction using Hibernate?

  - by user2519543

  Just wondering is there any difference when I beginTransaction [org.hibernate] before or after creating Criteria/Query etc.? example 1: ... Transaction tx= session.beginTransaction(); Criteria c = session.createCriteria(class); result = c.uniqueResult(); tx.commit(); ... example 2: ... Criteria c = session.createCriteria(class); Transaction tx= session.beginTransaction(); result = c.uniqueResult(); tx.commit(); ... Thanks.

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• Best Practice: Accessing radio button group

  - by seth

  Looking for the best, standards compliant, cross browser compatible, forwards compatible way to access a group of radio buttons in the DOM (this is closely related to my other most recent post...), without the use of any external libraries. <input type="radio" value="1" name="myRadios" />One<br /> <input type="radio" value="2" name="myRadios" />Two<br /> I've read conflicting information on getElementsByName(), which seems like the proper way to do this, but I'm unclear if this is a standards compliant, forwards compatible solution. Perhaps there is a better way?

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• Can a Snapshot transaction fail and only partially commit in a TransactionScope?

  - by Travis Brooks

  Greetings I stumbled onto a problem today that seems sort of impossible to me, but its happening...I'm calling some database code in c# that looks something like this: using(var tran = MyDataLayer.Transaction()) { MyDataLayer.ExecSproc(new SprocTheFirst(arg1, arg2)); MyDataLayer.CallSomethingThatEventuallyDoesLinqToSql(arg1, argEtc); tran.Commit(); } I've simplified this a bit for posting, but whats going on is MyDataLayer.Transaction() makes a TransactionScope with the IsolationLevel set to Snapshot and TransactionScopeOption set to Required. This code gets called hundreds of times a day, and almost always works perfectly. However after reviewing some data I discovered there are a handful of records created by "SprocTheFirst" but no corresponding data from "CallSomethingThatEventuallyDoesLinqToSql". The only way that records should exist in the tables I'm looking at is from SprocTheFirst, and its only ever called in this one function, so if its called and succeeded then I would expect CallSomethingThatEventuallyDoesLinqToSql would get called and succeed because its all in the same TransactionScope. Its theoretically possible that some other dev mucked around in the DB, but I don't think they have. We also log all exceptions, and I can find nothing unusual happening around the time that the records from SprocTheFirst were created. So, is it possible that a transaction, or more properly a declarative TransactionScope, with Snapshot isolation level can fail somehow and only partially commit?

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• How to handle dynamic site localizations?

  - by James Simpson

  I've got a website that is currently all in english. It is an online game, so it has a bunch of different pages with static text, as well as a lot of content in a database. I am trying to expand more globally and am gearing up to release some localizations of the site. However, I'm not sure about the best way to go about setting this up so that it'll be the easiest for me to manage and the easiest for users to use as well. Should I be storing the translated texts in a database, or should this be done in a completely different way? If it matters at all, the site is written in PHP and uses MySQL.

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• Which isolation level should I use for the following insert-if-not-present transaction?

  - by Steve Guidi

  I've written a linq-to-sql program that essentially performs an ETL task, and I've noticed many places where parallelization will improve its performance. However, I'm concerned about preventing uniquness constraint violations when two threads perform the following task (psuedo code). Record CreateRecord(string recordText) { using (MyDataContext database = GetDatabase()) { Record existingRecord = database.MyTable.FirstOrDefault(record.KeyPredicate()); if(existingRecord == null) { existingRecord = CreateRecord(recordText); database.MyTable.InsertOnSubmit(existingRecord); } database.SubmitChanges(); return existingRecord; } } In general, this code executes a SELECT statement to test for record existance, followed by an INSERT statement if the record doesn't exist. It is encapsulated by an implicit transaction. When two threads run this code for the same instance of recordText, I want to prevent them from simultaneously determining that the record doesn't exist, thereby both attempting to create the same record. An isolation level and explicit transaction will work well, except I'm not certain which isolation level I should use -- Serializable should work, but seems too strict. Is there a better choice?

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• Exit and rollback everything in script on error

  - by Jan W.

  Hey guys ! I'm in a bit of a pickle here. I have a TSQL script that does a lot of database structure adjustments but it's not really safe to just let it go through when something fails. to make things clear: using MS SQL 2005 it's NOT a stored procedure, just a script file (.sql) what I have is something in the following order BEGIN TRANSACTION ALTER Stuff GO CREATE New Stuff GO DROP Old Stuff GO IF @@ERROR != 0 BEGIN PRINT 'Errors Found ... Rolling back' ROLLBACK TRANSACTION RETURN END ELSE PRINT 'No Errors ... Committing changes' COMMIT TRANSACTION just to illustrate what I'm working with ... can't go into specifics now, the problem ... When I introduce an error (to test if things get rolled back), I get a statement that the ROLLBACK TRANSACTION could not find a corresponding BEGIN TRANSACTION. This leads me to believe that something when REALLY wrong and the transaction was already killed. what I also noticed is that the script didn't fully quit on error and thus DID try to execute every statement after the error occured. (I noticed this when new tables showed up when I wasn't expecting them because it should have rollbacked) any help in this department is welcome if more speficics are needed, ask! greetz

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• Find Group size in active directory

  - by Ilya Biryukov

  Hey I have the following code. I get a directory entry for a user (strpath). And then I get the groups where the user is listed. How can I get the number of users in each group? DirectoryEntry myDE = new System.DirectoryServices.DirectoryEntry(strpath); object obGroups = myDE.Invoke("Groups"); foreach (object ob in (IEnumerable)obGroups) { DirectoryEntry obGpEntry = new DirectoryEntry(ob); GroupsListBox.Items.Add(obGpEntry.Name ); }

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• Is it necessary to write ROLLBACK if queries fail?

  - by Donator

  I write mysql_query("SET AUTOCOMMIT=0"); mysql_query("START TRANSACTION"); before I write all queries. Then check if all of them are true and then write: mysql_query("COMMIT"); But if one of query fails, I just pass COMMIT query. So do I really need ROLLBACK function if one of the queries fail? Because without ROLLBACK it also works. Thanks.

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• LINQ - group specific types of classes

  - by Nelson

  This question is similar to http://stackoverflow.com/questions/2835192/linq-group-one-type-of-item but handled in a more generic way. I have a List that has various derived classes. I may have something like this: List<BaseClass> list = new List<BaseClass>() { new Class1(1), new Class2(1), new Class1(2), new Class3(1), new Class2(2), new Class4(1), new Class3(2) }; I am trying to use LINQ to semi-sort the list so that the natural order is maintained EXCEPT for certain classes which have base.GroupThisType == true. All classes with GroupThisType should be grouped together at the place that the first class of the same type occurs. Here is what the output should be like: List<BaseClass> list = new List<BaseClass>() { new Class1(1), new Class1(2), new Class2(1), new Class3(1), new Class3(2) new Class2(2), new Class4(1), };

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• What happens if a message is rolled back in MQ?

  - by Manglu

  Hi, I receive a message from a WebSPhere MQ queue. I try to process and if i receive some exceptions i want to rollback the message to the MQ Queue. I have no problems in doing the same. What happens to the message? Does it go to the bottom of the queue? If i try and pull a message from the queue would i receive the same message that i rolledback? What is the behaviour likely to be? I want to know this behaviour typically in a high volume Queue scenario? Appreciate any inputs. Thanks, Manglu

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