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sql server programming
group:Preventing Deadlock
sql server programming:
Trace 1204 has narrowed the cause of deadlock to these delete statements.
There are a total of 10 delete statements in this SP. create procedure del_emp @empid int Delete from tbl_employees where empid in (Select empid from tbl_location where empid = @empid) Delete from tbl_management where mge_ID in (Select mge_ID from tbl_sunmanagement where empid = @empid) ......... ......... Questions: 1. should i add (nolock) within the select statement? ex: Select empid from tbl_location WITH (NOLOCK) 2. should i add (updlock) within the delete statement? ex: Delete from tbl_employees WITH (UPDLOCK) Any suggestions highly appreciated.
Hi
To prevent deadlocks first of all you have to access table in the same order. That means if Connection1 runs DELETE tbl_employees and Delete from tbl_management so the Connection2 has to touch tbl_employees and tbl_management in the same order. I don't know your business requirements so design your application properly Regarding NOLOCK hint I'd say you can get dirty data and again it may or may not accepted by your requirements [quoted text, click to view] "morphius" <morphius@discussions.microsoft.com> wrote in message news:79328F46-6C5E-4424-A29F-275654225E5E@microsoft.com... > Trace 1204 has narrowed the cause of deadlock to these delete statements. > There are a total of 10 delete statements in this SP. > > create procedure del_emp @empid int > > Delete from tbl_employees > where empid in (Select empid from tbl_location where empid = @empid) > > Delete from tbl_management > where mge_ID in (Select mge_ID from tbl_sunmanagement where empid = > @empid) > > ........ > ........ > > Questions: > 1. should i add (nolock) within the select statement? ex: Select empid > from > tbl_location WITH (NOLOCK) > 2. should i add (updlock) within the delete statement? ex: Delete from > tbl_employees WITH (UPDLOCK) > > Any suggestions highly appreciated. > > >
UPDLOCK can reduce the chance of deadlocks but at the expense of concurrent
operations. Although you might view fast response time as performance, I think it's better to distinguish between performance (query/index tuning) and concurrency (blocking, deadlocking) so you can address the underlying causes. Performance and concurrency are closely related, though; the faster queries run, the less likely you will run into concurrency problems . Of course, you'll ultimately need to address both for the best response time. [quoted text, click to view] > Do you recommend UPDLOCK, READPAST to improve performance? Did you examine the execution plans for scans? Are the delete statements run as part of a transaction? UPDLOCK is ok but I would be wary of using READPAST except in special situations. -- Hope this helps. Dan Guzman SQL Server MVP [quoted text, click to view] "morphius" <morphius@discussions.microsoft.com> wrote in message
news:3C7A531D-CD07-44BA-A782-ECA299EFBE69@microsoft.com... > Hi Dan, > I've used the UPDLOCK and it prevented the deadlocks, however it slowed > down > the SP it takes a while to finish but it works. Do you recommend UPDLOCK, > READPAST to improve performance? > Thank you! > > "Dan Guzman" wrote: > >> > The PADLOCK hint >> >> Sorry, should be UPDLOCK. Damn spell checker :-) >> >> -- >> Hope this helps. >> >> Dan Guzman >> SQL Server MVP >> >> "Dan Guzman" <guzmanda@nospam-online.sbcglobal.net> wrote in message >> news:1F917170-D039-4C95-9D14-5E3DE97F3FE9@microsoft.com... >> >> 1. should i add (nolock) within the select statement? ex: Select empid >> >> from >> >> tbl_location WITH (NOLOCK) >> > >> > Only if it's acceptable to accidentally delete the wrong data or skip >> > data >> > that should be deleted. >> > >> >> 2. should i add (updlock) within the delete statement? ex: Delete from >> >> tbl_employees WITH (UPDLOCK) >> > >> > Since you have no explicit transaction (at least in your post), each >> > delete statement is in an independent atomic transaction. The PADLOCK >> > hint has little value in that case. A UPDLOCK, HOLDLOCK hint might be >> > appropriate in your SELECT subqueries if you have an explicit >> > transaction >> > and the row is subsequently deleted. >> > >> > In addition to Uri's suggestion about the delete order, I suggest you >> > review the execution plans to avoid scans and tune indexes/queries >> > accordingly. Scans greatly increase deadlock likelihood because more >> > rows >> > are accessed than needed and the performance hit results in more >> > concurrent queries. >> > >> > -- >> > Hope this helps. >> > >> > Dan Guzman >> > SQL Server MVP >> > >> > "morphius" <morphius@discussions.microsoft.com> wrote in message >> > news:79328F46-6C5E-4424-A29F-275654225E5E@microsoft.com... >> >> Trace 1204 has narrowed the cause of deadlock to these delete >> >> statements. >> >> There are a total of 10 delete statements in this SP. >> >> >> >> create procedure del_emp @empid int >> >> >> >> Delete from tbl_employees >> >> where empid in (Select empid from tbl_location where empid = @empid) >> >> >> >> Delete from tbl_management >> >> where mge_ID in (Select mge_ID from tbl_sunmanagement where empid = >> >> @empid) >> >> >> >> ........ >> >> ........ >> >> >> >> Questions: >> >> 1. should i add (nolock) within the select statement? ex: Select empid >> >> from >> >> tbl_location WITH (NOLOCK) >> >> 2. should i add (updlock) within the delete statement? ex: Delete from >> >> tbl_employees WITH (UPDLOCK) >> >> >> >> Any suggestions highly appreciated. >> >> >> >> >> >> >> > >>
Hi Dan,
I've used the UPDLOCK and it prevented the deadlocks, however it slowed down the SP it takes a while to finish but it works. Do you recommend UPDLOCK, READPAST to improve performance? Thank you! [quoted text, click to view] "Dan Guzman" wrote:
> > The PADLOCK hint > > Sorry, should be UPDLOCK. Damn spell checker :-) > > -- > Hope this helps. > > Dan Guzman > SQL Server MVP > > "Dan Guzman" <guzmanda@nospam-online.sbcglobal.net> wrote in message > news:1F917170-D039-4C95-9D14-5E3DE97F3FE9@microsoft.com... > >> 1. should i add (nolock) within the select statement? ex: Select empid > >> from > >> tbl_location WITH (NOLOCK) > > > > Only if it's acceptable to accidentally delete the wrong data or skip data > > that should be deleted. > > > >> 2. should i add (updlock) within the delete statement? ex: Delete from > >> tbl_employees WITH (UPDLOCK) > > > > Since you have no explicit transaction (at least in your post), each > > delete statement is in an independent atomic transaction. The PADLOCK > > hint has little value in that case. A UPDLOCK, HOLDLOCK hint might be > > appropriate in your SELECT subqueries if you have an explicit transaction > > and the row is subsequently deleted. > > > > In addition to Uri's suggestion about the delete order, I suggest you > > review the execution plans to avoid scans and tune indexes/queries > > accordingly. Scans greatly increase deadlock likelihood because more rows > > are accessed than needed and the performance hit results in more > > concurrent queries. > > > > -- > > Hope this helps. > > > > Dan Guzman > > SQL Server MVP > > > > "morphius" <morphius@discussions.microsoft.com> wrote in message > > news:79328F46-6C5E-4424-A29F-275654225E5E@microsoft.com... > >> Trace 1204 has narrowed the cause of deadlock to these delete statements. > >> There are a total of 10 delete statements in this SP. > >> > >> create procedure del_emp @empid int > >> > >> Delete from tbl_employees > >> where empid in (Select empid from tbl_location where empid = @empid) > >> > >> Delete from tbl_management > >> where mge_ID in (Select mge_ID from tbl_sunmanagement where empid = > >> @empid) > >> > >> ........ > >> ........ > >> > >> Questions: > >> 1. should i add (nolock) within the select statement? ex: Select empid > >> from > >> tbl_location WITH (NOLOCK) > >> 2. should i add (updlock) within the delete statement? ex: Delete from > >> tbl_employees WITH (UPDLOCK) > >> > >> Any suggestions highly appreciated. > >> > >> > >> > >
Dan,
A transaction is explicitly started outside this procedure and between 100-300 users could be using the transaction simultaneously. [quoted text, click to view] "Dan Guzman" wrote:
> > The PADLOCK hint > > Sorry, should be UPDLOCK. Damn spell checker :-) > > -- > Hope this helps. > > Dan Guzman > SQL Server MVP > > "Dan Guzman" <guzmanda@nospam-online.sbcglobal.net> wrote in message > news:1F917170-D039-4C95-9D14-5E3DE97F3FE9@microsoft.com... > >> 1. should i add (nolock) within the select statement? ex: Select empid > >> from > >> tbl_location WITH (NOLOCK) > > > > Only if it's acceptable to accidentally delete the wrong data or skip data > > that should be deleted. > > > >> 2. should i add (updlock) within the delete statement? ex: Delete from > >> tbl_employees WITH (UPDLOCK) > > > > Since you have no explicit transaction (at least in your post), each > > delete statement is in an independent atomic transaction. The PADLOCK > > hint has little value in that case. A UPDLOCK, HOLDLOCK hint might be > > appropriate in your SELECT subqueries if you have an explicit transaction > > and the row is subsequently deleted. > > > > In addition to Uri's suggestion about the delete order, I suggest you > > review the execution plans to avoid scans and tune indexes/queries > > accordingly. Scans greatly increase deadlock likelihood because more rows > > are accessed than needed and the performance hit results in more > > concurrent queries. > > > > -- > > Hope this helps. > > > > Dan Guzman > > SQL Server MVP > > > > "morphius" <morphius@discussions.microsoft.com> wrote in message > > news:79328F46-6C5E-4424-A29F-275654225E5E@microsoft.com... > >> Trace 1204 has narrowed the cause of deadlock to these delete statements. > >> There are a total of 10 delete statements in this SP. > >> > >> create procedure del_emp @empid int > >> > >> Delete from tbl_employees > >> where empid in (Select empid from tbl_location where empid = @empid) > >> > >> Delete from tbl_management > >> where mge_ID in (Select mge_ID from tbl_sunmanagement where empid = > >> @empid) > >> > >> ........ > >> ........ > >> > >> Questions: > >> 1. should i add (nolock) within the select statement? ex: Select empid > >> from > >> tbl_location WITH (NOLOCK) > >> 2. should i add (updlock) within the delete statement? ex: Delete from > >> tbl_employees WITH (UPDLOCK) > >> > >> Any suggestions highly appreciated. > >> > >> > >> > >
[quoted text, click to view]
> 1. should i add (nolock) within the select statement? ex: Select empid > from > tbl_location WITH (NOLOCK) Only if it's acceptable to accidentally delete the wrong data or skip data that should be deleted. [quoted text, click to view] > 2. should i add (updlock) within the delete statement? ex: Delete from > tbl_employees WITH (UPDLOCK) Since you have no explicit transaction (at least in your post), each delete statement is in an independent atomic transaction. The PADLOCK hint has little value in that case. A UPDLOCK, HOLDLOCK hint might be appropriate in your SELECT subqueries if you have an explicit transaction and the row is subsequently deleted. In addition to Uri's suggestion about the delete order, I suggest you review the execution plans to avoid scans and tune indexes/queries accordingly. Scans greatly increase deadlock likelihood because more rows are accessed than needed and the performance hit results in more concurrent queries. -- Hope this helps. Dan Guzman SQL Server MVP [quoted text, click to view] "morphius" <morphius@discussions.microsoft.com> wrote in message
news:79328F46-6C5E-4424-A29F-275654225E5E@microsoft.com... > Trace 1204 has narrowed the cause of deadlock to these delete statements. > There are a total of 10 delete statements in this SP. > > create procedure del_emp @empid int > > Delete from tbl_employees > where empid in (Select empid from tbl_location where empid = @empid) > > Delete from tbl_management > where mge_ID in (Select mge_ID from tbl_sunmanagement where empid = > @empid) > > ........ > ........ > > Questions: > 1. should i add (nolock) within the select statement? ex: Select empid > from > tbl_location WITH (NOLOCK) > 2. should i add (updlock) within the delete statement? ex: Delete from > tbl_employees WITH (UPDLOCK) > > Any suggestions highly appreciated. > > >
[quoted text, click to view]
> The PADLOCK hint Sorry, should be UPDLOCK. Damn spell checker :-) -- Hope this helps. Dan Guzman SQL Server MVP [quoted text, click to view] "Dan Guzman" <guzmanda@nospam-online.sbcglobal.net> wrote in message
news:1F917170-D039-4C95-9D14-5E3DE97F3FE9@microsoft.com... >> 1. should i add (nolock) within the select statement? ex: Select empid >> from >> tbl_location WITH (NOLOCK) > > Only if it's acceptable to accidentally delete the wrong data or skip data > that should be deleted. > >> 2. should i add (updlock) within the delete statement? ex: Delete from >> tbl_employees WITH (UPDLOCK) > > Since you have no explicit transaction (at least in your post), each > delete statement is in an independent atomic transaction. The PADLOCK > hint has little value in that case. A UPDLOCK, HOLDLOCK hint might be > appropriate in your SELECT subqueries if you have an explicit transaction > and the row is subsequently deleted. > > In addition to Uri's suggestion about the delete order, I suggest you > review the execution plans to avoid scans and tune indexes/queries > accordingly. Scans greatly increase deadlock likelihood because more rows > are accessed than needed and the performance hit results in more > concurrent queries. > > -- > Hope this helps. > > Dan Guzman > SQL Server MVP > > "morphius" <morphius@discussions.microsoft.com> wrote in message > news:79328F46-6C5E-4424-A29F-275654225E5E@microsoft.com... >> Trace 1204 has narrowed the cause of deadlock to these delete statements. >> There are a total of 10 delete statements in this SP. >> >> create procedure del_emp @empid int >> >> Delete from tbl_employees >> where empid in (Select empid from tbl_location where empid = @empid) >> >> Delete from tbl_management >> where mge_ID in (Select mge_ID from tbl_sunmanagement where empid = >> @empid) >> >> ........ >> ........ >> >> Questions: >> 1. should i add (nolock) within the select statement? ex: Select empid >> from >> tbl_location WITH (NOLOCK) >> 2. should i add (updlock) within the delete statement? ex: Delete from >> tbl_employees WITH (UPDLOCK) >> >> Any suggestions highly appreciated. >> >> >> >
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