READPAST Example
Jul 31, 2001Does anyone have an example on how to make use of READPAST and ROWLOCK so that when a SELECT statement retrieves a record, other SELECT statements will 'Read Past' that record until it is unlocked?
Thanks!
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(readpast Readcommitted) Vs (readpast Repeatableread) Vs Readpast
Sep 25, 2007
What is the difference among them ? who can tell ?
select * from table (readpast readcommitted)
select * from table (readpast repeatableread)
select * from table (readpast)
I suppose they are the same as readpast.
I cannot tell the differece.
thank you
NoLock Vs ReadPast
Oct 25, 2006I have been experiencing deadlock errors with two stored procs that I am using.
SP1 is a read query that gets all unprocessed orders (status = 0)
SP2 is an insert query that inserts new orders (Status = 0) uses a transaction.
I have a multithreaded application and once in a while the read query (SP1) will try to read a new row that has just been inserted but not committed yet hence the deadlock arises.
If i use a hint "With(NoLocks)" this will be a dirty read and still read the uncommitted insert from SP2 - is this correct?
Where as if I use hint "With(ReadPast)" this will now only read committed rows and hence the deadlock should not arise - it will not read any uncommitted rows - Correct?
So I think that it is better to use READPAST than NOLOCK. Any orders that have status = 0 not picked up will get picked up on the next round when SP1 is executed again.
Any thougths or suggestions are always appreciated.
Jawahar
NOLOCK And READPAST On Same Table?
Sep 17, 2005Is it possible to use With (NOLOCK) and With (READPAST) in the sameSELECT query and what whould be the syntax?@param intSELECTmyRowFROMdbo.myTable WITH (NOLOCK)WHEREmyRow = @paramThanks,lq
View 6 Replies View RelatedWith Readpast Changing Isloation Level
Nov 2, 2007We have an application that accesses a SQL Server 2005 database. The isolation level is set to Read Committed. When the app calls a procedure to insert,update, or delete it seems to change the isolation level after the commit. After the commit, it calls another proc to fill a drop down and it gets the following message
"You can only specify the READPAST lock in the READ COMMITTED or REPEATABLE READ isolation levels"
The proc that fills the drop down isn't even using a with readpast command, but it is being used in some of the procs used prior to the commit.
Does anyone have any ideas?
Queue Processing Using Updlock, Readpast Locking Hints
Apr 25, 2008This article instructed me on how to process rows from a table used as a data queue for multiple processes.
http://www.mssqltips.com/tip.asp?tip=1257
I tested this against the AdventureWorks DB (SQL 2005) and multiple SQL connections inside of Sql Mgmt. Studio).
Connection1:
BEGIN TRANSACTION
SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) --skips over locked rows
--COMMIT TRANSACTION
Connection2:
BEGIN TRANSACTION
SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) --skips over locked rows
COMMIT TRANSACTION
This works like I want where connection 2 skips over the locked row from connection 1 and gets the next available record from the table / queue. However, when I add ORDER BY tsql to each sql statement, connection 2 is now blocked waiting for Connection 1 to commit. (This is not what I want)
Connection1:
BEGIN TRANSACTION
SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) order by DueDate
--COMMIT TRANSACTION
Connection2:
BEGIN TRANSACTION
SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) order by DueDate --is blocked until connection 1 commits transaction
COMMIT TRANSACTION
How do I prevent blocking when using these locking hints with ORDER BY?
thanks