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Recently I had a deadlock problem because Sql Server locks more then necessary page. You can't really do anything against it. Now we are catching deadlock exceptions Edit: We are using snapshot isolation meanwhile, which solves many, but not all of the problems. Unfortunately, to be able to use snapshot isolation it must be allowed by the database server, which may cause unnecessary problems at customers site. Now we are not only catching deadlock exceptions which still can occur, of course but also snapshot concurrency problems to repeat transactions from background processes which cannot be repeated by the user.
But this still performs much better than before. I have a similar problem, I want to lock only 1 row. So, if you don't define a index to direct access to the row, all the preceded rows will be locked. In your example:. Asume that you have a table named TBL with an id field. You need to define a index for the field id or any other fields that are involved in you select :.
You cannot have snapshot isolation and blocking reads at the same time. The purpose of snapshot isolation is to prevent blocking reads. The full answer could delve into the internals of the DBMS. It depends on how the query engine which executes the query plan generated by the SQL optimizer operates. You can also run into problems if the DBMS applies page-level locking by default; locking one row locks the entire page and all the rows on that page.
There are some ways you could debunk this as the source of trouble. The database does not have to be in single-user mode. OK, a single select wil by default use "Read Committed" transaction isolation which locks and therefore stops writes to that set. You can change the transaction isolation level with. The escalation goes to page, then table lock.
I'm assuming you don't want any other session to be able to read the row while this specific query is running Question - is this case proven to be the result of lock escalation i. If so, there is a full explanation and a rather extreme workaround by enabling a trace flag at the instance level to prevent lock escalation.
If you are deliberately locking a row and keeping it locked for an extended period, then using the internal locking mechanism for transactions isn't the best method in SQL Server at least. All the optimization in SQL Server is geared toward short transactions - get in, make an update, get out.
That's the reason for lock escalation in the first place. So if the intent is to "check out" a row for a prolonged period, instead of transactional locking it's best to use a column with values and a plain ol' update statement to flag the rows as locked or not. Application locks are one way to roll your own locking with custom granularity while avoiding "helpful" lock escalation. MSSQL often escalates those row locks to page-level locks even table-level locks, if you don't have index on field you are querying , see this explanation.
So the advice on that site is not applicable to your problem. I solved the rowlock problem in a completely different way. I realized that sql server was not able to manage such a lock in a satisfying way.
I choosed to solve this from a programatically point of view by the use of a mutex How about trying to do a simple update on this row first without really changing any data? After that you can proceed with the row like in was selected for update. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 12 years, 3 months ago. Active 7 years, 1 month ago.
Viewed k times. Improve this question. Bill Paetzke Using above two methods together, we can construct a paging component in our web or Swing application.
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