SQL server update statements cause deadlocks - sql-server-2005

Question

I have an application which is running multiple sql statements simultaneously in different threads, causing various deadlocks which all seem to come from one table. For example the two update statements below:
UPDATE WF SET QUEUETIME='2011-02-18 13:06:53.578', STATE = 'outbound', USER = '', TIME = null
WHERE PID = 'MessageProcessing' AND ACTIVITYID = 'Delete' AND ITEMID = '120' AND TRANID = 'Created' AND STATE = 'ready' AND USER = ''
UPDATE WF SET QUEUETIME='2011-02-18 13:06:53.625', STATE = 'ready', USER = '', TIME = null
WHERE PID = 'standardOutbound' AND ACTIVITYID = 'Node1' AND ITEMID = '121' AND TRANID = 'toNode1' AND STATE = '' AND USER = ''
produce the following deadlock:
<deadlock-list>
<deadlock victim="process6d8e38">
<process-list>
<process id="process6d8e38" taskpriority="0" logused="272" waitresource="RID: 7:1:564:14" waittime="625" ownerId="430343" transactionname="implicit_transaction" lasttranstarted="2011-02-18T13:06:53.640" XDES="0xb44a258" lockMode="U" schedulerid="1" kpid="2632" status="suspended" spid="58" sbid="0" ecid="0" priority="0" transcount="2" lastbatchstarted="2011-02-18T13:06:53.640" lastbatchcompleted="2011-02-18T13:06:53.640" clientapp="jTDS" hostname="INTERWOV-FP1" hostpid="123" loginname="database1" isolationlevel="read committed (2)" xactid="430343" currentdb="7" TIMEout="4294967295" clientoption1="671088672" clientoption2="128058">
<executionStack>
<frame procname="adhoc" line="1" stmtstart="336" sqlhandle="0x0200000077e2b21749c20d3ca2ca8d4d89ea5ea29336e03e">
UPDATE WF SET QUEUETIME = #P0 , STATE = #P1 , USER = #P2 , TIME = #P3 WHERE PID = #P4 AND ACTIVITYID = #P5 AND ITEMID = #P6 AND TRANID = #P7 AND STATE = #P8 AND USER = #P9 </frame>
</executionStack>
<inputbuf>
(#P0 datetime,#P1 nvarchar(4000),#P2 nvarchar(4000),#P3 datetime,#P4 nvarchar(4000),#P5 nvarchar(4000),#P6 int,#P7 nvarchar(4000),#P8 nvarchar(4000),#P9 nvarchar(4000))UPDATE WF SET QUEUETIME = #P0 , STATE = #P1 , USER = #P2 , TIME = #P3 WHERE PID = #P4 AND ACTIVITYID = #P5 AND ITEMID = #P6 AND TRANID = #P7 AND STATE = #P8 AND USER = #P9 </inputbuf>
</process>
<process id="process8ccb68" taskpriority="0" logused="900" waitresource="RID: 7:1:564:12" waittime="625" ownerId="430341" transactionname="implicit_transaction" lasttranstarted="2011-02-18T13:06:53.623" XDES="0xaeccf48" lockMode="U" schedulerid="2" kpid="312" status="suspended" spid="53" sbid="0" ecid="0" priority="0" transcount="2" lastbatchstarted="2011-02-18T13:06:53.640" lastbatchcompleted="2011-02-18T13:06:53.623" clientapp="jTDS" hostname="INTERWOV-FP1" hostpid="123" loginname="database1" isolationlevel="read committed (2)" xactid="430341" currentdb="7" TIMEout="4294967295" clientoption1="671088672" clientoption2="128058">
<executionStack>
<frame procname="adhoc" line="1" stmtstart="336" sqlhandle="0x0200000077e2b21749c20d3ca2ca8d4d89ea5ea29336e03e">
UPDATE WF SET QUEUETIME = #P0 , STATE = #P1 , USER = #P2 , TIME = #P3 WHERE PID = #P4 AND ACTIVITYID = #P5 AND ITEMID = #P6 AND TRANID = #P7 AND STATE = #P8 AND USER = #P9 </frame>
</executionStack>
<inputbuf>
(#P0 datetime,#P1 nvarchar(4000),#P2 nvarchar(4000),#P3 datetime,#P4 nvarchar(4000),#P5 nvarchar(4000),#P6 int,#P7 nvarchar(4000),#P8 nvarchar(4000),#P9 nvarchar(4000))UPDATE WF SET QUEUETIME = #P0 , STATE = #P1 , USER = #P2 , TIME = #P3 WHERE PID = #P4 AND ACTIVITYID = #P5 AND ITEMID = #P6 AND TRANID = #P7 AND STATE = #P8 AND USER = #P9 </inputbuf>
</process>
</process-list>
<resource-list>
<ridlock fileid="1" pageid="564" dbid="7" objectname="database1.dbo.WF" id="lock3a63dc0" mode="X" associatedObjectId="72057594077577216">
<owner-list>
<owner id="process6d8e38" mode="X"/>
</owner-list>
<waiter-list>
<waiter id="process8ccb68" mode="U" requestType="wait"/>
</waiter-list>
</ridlock>
<ridlock fileid="1" pageid="564" dbid="7" objectname="database1.dbo.WF" id="lock3a65f40" mode="X" associatedObjectId="72057594077577216">
<owner-list>
<owner id="process8ccb68" mode="X"/>
</owner-list>
<waiter-list>
<waiter id="process6d8e38" mode="U" requestType="wait"/>
</waiter-list>
</ridlock>
</resource-list>
</deadlock>
</deadlock-list>
I realise some amount of deadlocks are inevitable and the application should handle them (which it does), but I don't understand why they should be happening in this case. In my simplistic mind these two statements should be locking different rows, and even if they were updating the same row, one should just wait for the other.
Can anyone explain why they are causing deadlocks, or give any suggestions as to how to prevent them?
We have 3 non-clustered indexes on the table (PID, ACTIVITYID, ITEMID, TRANID), (ITEMID), and (PID, ACTIVITYID). (PID, ACTIVITYID, ITEMID, TRANID) form the primary key. I've tried (somewhat blindly) playing about with the indexes, but seemingly to no avail.
The application is running on weblogic and sql server 2005, and I've reproduced the deadlocks on websphere and sql server 2008. The don't seem to occur when using an oracle database, but this is unfortunately not an option for our client!
Many thanks to anyone who can offer help or insight into this.

Answer 1

Problem are usually not updates alone, but combination of selects and updates. Consider scenario, where transaction selects some row and then updates it. If two such transactions run parallel, deadlock occurs.
Simplest solution is use UPDLOCK (and optionally ROWLOCK) hint in select statements; of course only for records, updated after - otherwise you may end in slow application.

Answer 2

Is there any clustered index? Any indexed views? Any other indexes? The columns being updated don't appear to be in any indexes. Row-level locking should be fine, but something must be causing an escalation. The sets appear to be disjoint, but perhaps the pages are overlapping (hence my question about the choice of clustered index).
http://msdn.microsoft.com/en-us/library/ms184286.aspx