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    <p>When you perform the <code>select</code>, place a <code>updlock</code>, <code>holdlock</code> on the range being selected:</p> <pre><code>begin transaction if not exists( select id from [ua_subset_composite] with (updlock, holdlock) where ua = 'sadsadsad') begin insert into [ua_subset_composite] select 'sadsadsad',1,null,null,null,null end commit </code></pre> <p>The <code>holdlock</code>, equivalent to the <a href="http://msdn.microsoft.com/en-us/library/ms173763.aspx" rel="nofollow"><code>serializable</code> isolation level</a>, will have the following effect:</p> <blockquote> <ul> <li><p>Statements cannot read data that has been modified but not yet committed by other transactions.</p></li> <li><p>No other transactions can modify data that has been read by the current transaction until the current transaction completes.</p></li> <li><p>Other transactions cannot insert new rows with key values that would fall in the range of keys read by any statements in the current transaction until the current transaction completes.</p></li> </ul> <p>Range locks are placed in the range of key values that match the search conditions of each statement executed in a transaction. This blocks other transactions from updating or inserting any rows that would qualify for any of the statements executed by the current transaction. This means that if any of the statements in a transaction are executed a second time, they will read the same set of rows. The range locks are held until the transaction completes. This is the most restrictive of the isolation levels because it locks entire ranges of keys and holds the locks until the transaction completes. <strong>Because concurrency is lower, use this option only when necessary</strong>.</p> </blockquote> <p>The <code>updlock</code> is needed in addition to the <code>holdlock</code>... by adding the <code>updlock</code> we prevent a separate process from performing its own <code>select with (updlock, holdlock)</code> statement on the same range at the same time.</p>
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    1. POInserting records into DB table in multithreaded environment
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    1. USMichael Fredrickson
    1. USMichael Fredrickson
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    1. COwhat does it do to those attempting to insert? Bomb out their transaction?
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      1. USWoot4Moo
    2. CO@Woot4Moo Other processes trying to insert will be blocked, and wait for the blocking process to complete and release the lock before continuing. Won't bomb out necessarily, but will definitely reduce concurrency.
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      1. USMichael Fredrickson
    3. COOk, to clarify though, doesn't this cause dirty inserts/updates? I could be wrong, just trying to get some clarity.
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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