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POSQL Server 2008: U and X locks - deadlock on one table without any indexes. How?
 

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  1. POSQL Server 2008: U and X locks - deadlock on one table without any indexes. How?
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    <p>I observe really strange behavior of my DB. I have one small table (about 300 rows) where one field is continuously updated.</p> <p>And I was getting a lot of deadlocks there - update of the table was deadlocking the similar update of the same table (U lock vs X lock).</p> <p>So I decided to remove the clustered index (so table doesn't have any indexes now) to fix the deadlocks. But it didn't help and now I'm getting the deadlock between the U and X lock modes.</p> <p>So one table, no indexes and 2 sessions updating one table</p> <p><strong>Victim</strong></p> <pre><code>update dbo.MyNumber set @nextno = nextno = nextno + 1 where [type] = @type and yearid = @yearid </code></pre> <p><br/><strong>Winning query:</strong></p> <pre><code>update dbo.MyNumber set @nextno = nextno = nextno + 1 where [type] = @TYPE and yrclosedyn = 0 </code></pre> <p><strong>Rows are definitely different but the page is the same.</strong></p> <p>How Is it possible? Maybe it is connected to the lock escalation, or ...?</p> <p>I really appreciate any suggestions.</p> <p>Thanks in advance Mike</p> <p>DEADLOCK XML:</p> <pre><code>&lt;deadlock-list&gt; &lt;deadlock victim="process6c492e8"&gt; &lt;process-list&gt; &lt;process id="processb6a988" taskpriority="0" logused="1848" waitresource="RID: 5:1:127478:16" waittime="3478" ownerId="17153439" transactionname="user_transaction" lasttranstarted="2012-12-18T12:31:40.147" XDES="0xffffffff89482258" lockMode="U" schedulerid="7" kpid="4248" status="suspended" spid="98" sbid="0" ecid="0" priority="0" transcount="2" lastbatchstarted="2012-12-18T12:31:49.913" lastbatchcompleted="2012-12-18T12:31:49.913" clientapp="PenAIR" hostname="S16047425" hostpid="9300" loginname="sa" isolationlevel="read committed (2)" xactid="17153439" currentdb="5" lockTimeout="4294967295" clientoption1="673185824" clientoption2="128056"&gt; &lt;executionStack&gt; &lt;frame procname="MYDATABASE.dbo.MyStoredProcedure" line="92" stmtstart="9062" stmtend="9388" sqlhandle="0x030005002d15a05e58b5710016a100000100000000000000"&gt; UPDATE dbo.MyNumber Set @NEXTNO = NEXTNO = NEXTNO + 1 WHERE (TYPE = @TYPE) AND (YRCLOSEDYN = 0) &lt;/frame&gt; &lt;/executionStack&gt; &lt;inputbuf&gt; Proc [Database Id = 5 Object Id = 1587549485] &lt;/inputbuf&gt; &lt;/process&gt; &lt;process id="process6c492e8" taskpriority="0" logused="192" waitresource="RID: 5:1:127478:20" waittime="8252" ownerId="17153562" transactionname="user_transaction" lasttranstarted="2012-12-18T12:31:45.140" XDES="0x6583b1e0" lockMode="U" schedulerid="13" kpid="19824" status="suspended" spid="143" sbid="0" ecid="0" priority="0" transcount="2" lastbatchstarted="2012-12-18T12:31:45.140" lastbatchcompleted="2012-12-18T12:31:45.140" clientapp="PenAIR" hostname="S16047425" hostpid="4760" loginname="sa" isolationlevel="read committed (2)" xactid="17153562" currentdb="5" lockTimeout="4294967295" clientoption1="673185824" clientoption2="128056"&gt; &lt;executionStack&gt; &lt;frame procname="MYDATABASE.dbo.MyStoredProcedure" line="92" stmtstart="9062" stmtend="9388" sqlhandle="0x030005002d15a05e58b5710016a100000100000000000000"&gt; UPDATE dbo.MyNumber Set @NEXTNO = NEXTNO = NEXTNO + 1 WHERE ([TYPE] = @TYPE) AND (YRCLOSEDYN = 0) &lt;/frame&gt; &lt;/executionStack&gt; &lt;inputbuf&gt; Proc [Database Id = 5 Object Id = 1587549485] &lt;/inputbuf&gt; &lt;/process&gt; &lt;/process-list&gt; &lt;resource-list&gt; &lt;ridlock fileid="1" pageid="127478" dbid="5" objectname="MYDATABASE.dbo.MyNumber" id="lock464f2640" mode="X" associatedObjectId="72057594131120128"&gt; &lt;owner-list&gt; &lt;owner id="processb6a988" mode="X"/&gt; &lt;/owner-list&gt; &lt;waiter-list&gt; &lt;waiter id="process6c492e8" mode="U" requestType="wait"/&gt; &lt;/waiter-list&gt; &lt;/ridlock&gt; &lt;ridlock fileid="1" pageid="127478" dbid="5" objectname="MYDATABASE.dbo.MyNumber" id="lockfffffffff1974980" mode="X" associatedObjectId="72057594131120128"&gt; &lt;owner-list&gt; &lt;owner id="process6c492e8" mode="X"/&gt; &lt;/owner-list&gt; &lt;waiter-list&gt; &lt;waiter id="processb6a988" mode="U" requestType="wait"/&gt; &lt;/waiter-list&gt; &lt;/ridlock&gt; &lt;/resource-list&gt; &lt;/deadlock&gt; &lt;/deadlock-list&gt; </code></pre>
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      1. POSQL Server 2008: U and X locks - deadlock on one table without any indexes. How?
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    1. COWhy on earth did you think removing the clustered index would solve your deadlocks?? The locks happen on the data rows - whether or not you have a clustered index makes **no difference** whatsoever ....
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    2. COWhat are the queries involved and the deadlock graph?
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      1. USMartin Smith
    3. COAdded them in the post, sorry forgot about the queries
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      1. POSQL Server 2008: U and X locks - deadlock on one table without any indexes. How?
      1. USmike
 

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