Triggers

  • Hi,

    I would like to know the difference between disabling and dropping a trigger. To me, Trigger is basically coupled with transaction hence write/reads entry from the log for the action. If that is the case, disabling a trigger would only stop the read operation however the write happens to the transaction log. For a big table with more transactions(updates/delete/insert), it would be great if we can drop the trigger instead of disabling so I can save the log file growth. So dropping a trigger would be the best one rather than disabling if it is not going to use in future.

    Please correct me perhaps I am wrong on anything.

  • If you aren't going to use the trigger anymore, drop it. If you do plan on using it in the future, I would disable it. Another alternative is to script the trigger out and recreate it/drop it with a script or job.

  • Whether you have triggers on a table or not has no bearing on whether transactions are written to the transaction log. All transactional operations are logged (in all recovery models) so you will not gain anything tangible by dropping vs disabling a trigger.

    Also, triggers do not operate asyncronously, somehow mining the transaction log. They will be fired for each relevant DML statement as part of the same transaction.

  • Thanks for your comment!!!

    Am really looking for an answer or confirmation as how the disabling of a trigger is working. As I mentioned, is this the way that it will log an entry in transaction log but it wont read from it or it wont write the entry at all if it is in disabled state?

  • sqlchanakya (2/28/2011)


    Am really looking for an answer or confirmation as how the disabling of a trigger is working. As I mentioned, is this the way that it will log an entry in transaction log but it wont read from it or it wont write the entry at all if it is in disabled state?

    No, triggers have absolutely no effect on whether the original transaction gets logged to the transaction log.

  • Could you plese check the below link and correct me where I interpreted wrongly...

    http://sqlblogcasts.com/blogs/tonyrogerson/archive/2006/10/27/1248.aspx

  • Interesting...

    That is written for 2000 (this is the 2008 forum) - what it's saying is that because the inserted and deleted tables need to include all columns, not just the ones affected by the update, some operations may end up with increased logging information.

    I've never heard of this before and I can't see any official reference that supports it, but it does make some sense. I suspect that the huge changes between 2000 and 2008 will have changed this one way or another, however I'll see if I can do some digging (if one of the heavy weights hasn't answered it definitively by then)

  • Okei, In Paul Randal's blog, he mentioned for SQL 2005 or behind, they changed the way the trigger working. But I could not find how it works.

    I would really appreciate if you could help me on the same as you said....I would also definitely look and share the same.

  • So, to clarify, which version of SQL Server are you using?

  • SQL Server 2008; however 80 compatibility ....

  • HowardW (2/28/2011)


    sqlchanakya (2/28/2011)


    Am really looking for an answer or confirmation as how the disabling of a trigger is working. As I mentioned, is this the way that it will log an entry in transaction log but it wont read from it or it wont write the entry at all if it is in disabled state?

    No, triggers have absolutely no effect on whether the original transaction gets logged to the transaction log.

    IIRC, they can have an impact on whether minimal logging of bulk loads will take place. I don't believe that's the case here, though.

    --Jeff Moden


    RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
    First step towards the paradigm shift of writing Set Based code:
    ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

    Change is inevitable... Change for the better is not.


    Helpful Links:
    How to post code problems
    How to Post Performance Problems
    Create a Tally Function (fnTally)

  • I guess my question would be... what does the trigger do?

    --Jeff Moden


    RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
    First step towards the paradigm shift of writing Set Based code:
    ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

    Change is inevitable... Change for the better is not.


    Helpful Links:
    How to post code problems
    How to Post Performance Problems
    Create a Tally Function (fnTally)

  • Actually, we had a trigger which used to pull data from one db to another db using Service Broker. We changed currently the entire architecture as if we found critical issues in this case. However, we only disabled the triggers. As I read the article mentioned in my previous post, alos the table is undergoing high transactions(insert/update/delete), (replication is also set up on the DB) thought it would be great to stop there by reduce the transaction log size.

    From my googling, it was clear that in SQL server 2000, it is very mcuh true the case. Also it is mentioned trigger functionality had a great change in SQL Server 2005. Thought of understanding how it would have done in SQL server 2005 and later there by coming to a conclusion.

    Is there any link I can go through about this architectural change in Trigger. I am still googling out, but no clues so far...

  • In SQL 2005 and above, the inserted and deleted tables are materialised from the row version store in TempDB, not the transaction log. Hence they do not cause log reads any longer.

    Disabled trigger = metadata retained, trigger not executed at all

    Dropped trigger = metadata dropped, trigger completely removed.

    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
  • Thank you Gail!!! It is clear now.

    However a question behind is the change is applicable for the SQL version or its compatibility. In my case, Compatibility is 80 on SQL server 2008.

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