locking question

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locking question

hi2u

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November 19, 2012 at 3:14 pm

#393634

Hello,
For this scenario :
update Table1 with (TABLOCK, XLOCK)
...
then a "INSTEAD OF TRIGGER" on Table1 update Table1 with other value
Does the trigger keep the initial (TABLOCK, XLOCK) or the lock is released and another one is made for the trigger?
Thanks

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Bhuvnesh SSC Guru Points: 59351 More actions · Answer 1

hi2u (11/19/2012)
Does the trigger keep the initial (TABLOCK, XLOCK) or the lock is released and another one is made for the trigger?Thanks

Yes to maintain the atomicity there will be seperate LOCK

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)

hi2u Mr or Mrs. 500 Points: 502 More actions · Answer 2

hi2u

Mr or Mrs. 500

Points: 502

November 20, 2012 at 8:00 am

#1560821

Thank you for the info

Eugene Elutin SSC Guru Points: 59322 More actions · Answer 3

Bhuvnesh (11/19/2012)
hi2u (11/19/2012)
Does the trigger keep the initial (TABLOCK, XLOCK) or the lock is released and another one is made for the trigger?Thanks
Yes to maintain the atomicity there will be seperate LOCK

What do you mean "by separate LOCK"?

Intial locks placed on a table for UPDATE will be there until transaction is committed. INSTEAD OF trigger fires before SQL performs any change (not even change logging), so the only thing I can see may happen is LOCK escalation to the higher level...

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Gail Shaw SSC Guru Points: 1004504 More actions · Answer 4

hi2u (11/19/2012)
Hello,
For this scenario :
update Table1 with (TABLOCK, XLOCK)
...
then a "INSTEAD OF TRIGGER" on Table1 update Table1 with other value
Does the trigger keep the initial (TABLOCK, XLOCK) or the lock is released and another one is made for the trigger?

The exclusive table lock will be held until the end of the execution of the trigger.

Triggers execute within the transactions that fire them, exclusive locks are held until the end of the transaction, hence that lock will be held for the duration of the trigger's execution.

btw, you could have just used the TABLOCKX hint, that does the same as those two combined.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

hi2u Mr or Mrs. 500 Points: 502 More actions · Answer 5

Thank you for the clarification

GilaMonster (11/20/2012)
btw, you could have just used the TABLOCKX hint, that does the same as those two combined.

This thread showed me that i should not trust every forum post but i always thought this was not true because of this :

http://dbaspot.com/ms-sqlserver/140553-transaction-deadlock-tablelocks.html

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 6

hi2u (11/20/2012)
t i always thought this was not true because of this : http://dbaspot.com/ms-sqlserver/140553-transaction-deadlock-tablelocks.html

That thread's talking about SELECT and the locks it takes. You're talking about UPDATE. Very different locking behaviour in the default isolation level.

In read committed isolation (the default), shared locks taken by selects are released as soon as the statement completes (sometimes earlier), while the exclusive locks taken by insert, update and delete are held until the end of the transaction.

And yeah, unfortunately not everything posted in the forums is true. You have to consider the poster's history and check more than one source to be sure (or test if it's something testable).

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

hi2u Mr or Mrs. 500 Points: 502 More actions · Answer 7

hi2u

Mr or Mrs. 500

Points: 502

November 20, 2012 at 11:27 am

#1560951

well i learned something today.

Thank you !