UPDATE QUERY can't update table

Question

Hi,
During 1500-2000 concurrent users, DB Transaction locks occur. So that Update query can't update table and we get inconsistent data. How can we avoid this inconsistent data?? Why we get transaction locks??
Eg. In update query it update the status of user with completed; but because of transaction lock  update query can't update status of user it remains uncompleted. So we can get wrong status of user(inconsistent data). Why UPDATE query update the status
of user???
update table set status='completed', date=@p2,score=@p3 where id=@p1

Answer 1

You are not getting inconsistent data, you are getting the data according to the isolation level you are running under. The isolation level determines the locking model and therefore determines any bad dependencies you may experience. Reducing the bad dependencies
through higher isolation level will lower concurrency. *This* is the core concept of Transactional Processing theory.
Furthermore there is not really such a thing as a DB Transaction lock - at least not in the way you mean. SQL server does use DB locks (such as Shared transaction workspace and Exclusive transaction workspace) but the highest level of lock escalation is
the object level (heap or btree) so those are the things you are really interested in. In the ideal would you want all Exclusive, Shared and U locks to be taken at the RID (heaps) or Key (cluster tables) level - and only have few of them per query.
In conclusion think carefully about your query and how it is implimented under the covers by the database engine.
Regards,
Mark Broadbent.
Microsoft Certified Master
Contact me through twitter |
blog | sqlcloud
Please click "Propose as answer" if a post solves your problem
or/and vote the post up if it's been helpful.