StackOverflow2013

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17975753
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2013-07-31T16:22:00.967
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2013-07-31T17:08:10.663
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2013-07-31T17:08:10.663
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As suggested by Phil, I used optimistic concurrency to ensure the job could not be processed more than once. I realised that rather than having to add a dedicated <code>rowversion</code> column I could use the IsLocked bit column as the <code>ConcurrencyToken</code>. Semantically, if this value has changed since we retrieved the row, the update should fail since only one processor should ever be able to lock it. I used the <a href="http://msdn.microsoft.com/en-us/data/jj591617#1.12" rel="nofollow">fluent API</a> as below to configure this, although I could also have used the <a href="http://msdn.microsoft.com/en-us/data/gg193958.aspx" rel="nofollow">ConcurrencyCheck data annotation</a>. <pre><code>protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<QueueItem>() .Property(p => p.IsLocked) .IsConcurrencyToken(); } </code></pre> I was then able to simple the <code>CollectQueueItem</code> method, losing the TransactionScope entirely and catching the more <code>DbUpdateConcurrencyException</code>. <pre><code>public OperationQueueItem CollectQueueItem() { try { var queueItem = this.QueueItems.FirstOrDefault(qi => !qi.IsLocked); if (queueItem != null) { queueItem.DateCollected = DateTime.UtcNow; queueItem.IsLocked = true; this.SaveChanges(); return queueItem; } } catch (DbUpdateConcurrencyException) //someone else grabbed the job. { } return null; } </code></pre> I reran the tests, you can see it's a great compromise. No duplicates, nearly 100x faster than with <code>REPEATABLE READ</code>, and no <code>DEADLOCKS</code> so the DBAs won't be on my case. Awesome! <pre><code>//Optimistic Concurrency: //Elapsed time: 00:00:00.5065586 //Deadlocked: 624 //Duplicates: 0 </code></pre>
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1. POCode First - Retrieve and Update Record in a Transaction without Deadlocks
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PostTypePostTypeId
1. PTAnswer
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1. USJoe Taylor
UserOwnerUserId
1. USJoe Taylor
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