Select (nolock)
Mar 11, 2008Hi, I get an error when select * from a table with nolock....please help.
Cannot specify an index or locking hint for a remote data source
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Select With Nolock Has Calculation Risk??
Apr 8, 2008Hi all,
I just read this article. The kind of select is called dirty read.
So select with nolock might have inaccurate result...? PLEASE COMMENT ON THIS. I am using it to count some huge tables, and has problem on the result..
http://www.4guysfromrolla.com/webtech/101100-1.2.shtml
NOLOCK
Using NOLOCK politely asks SQL Server to ignore locks and read directly from the tables. This means you completely circumvent the lock system, which is a major performance and scalability improvement. However, you also completely circumvent the lock system, which means your code is living dangerously. You might read the not-necessarily-valid uncommitted modifications of a running transaction. This is a calculated risk.
For financial code and denormalized aggregates (those little counters of related data that you stash away and try desperately to keep accurate), you should play it safe and not use this technique.
Select With (nolock) OR TransactionScope With Option Read Uncommitted Data
May 29, 2007Hi Sql gurus :))I've got a question that I couldn't find a satisfying answer on the net.What is the difference between:1) running sql query (select from sth with nolock) with no transaction2) running sql query (select from sth) withing a TransactionScope with option Read Uncommitted dataBasically, both should do the same work. However is anyone aware of any potential problems using any of both approaches ?We use 1) to improve our web application scalability since the system works in such a way that any selects and updates on that table (sth) do not interfere with one another.However, updates are done in a TransactionScope. And when having simultaneous select with nolock and update in a Transaction scope (the select statement has a where clause and returns records that are not updated by the update statement). However sometimes ( we still cannot figure it out when) the select statement returns some records twice.For example, the select should return 1000 records , but (sometimes) it returns 1002 records ( the extra 2 records are copies of some of the original 1000 records).Removing the nolock, makes the problem does not appear - but i want to be 100% sure that nolock is our troublemaker. And if it is - why ?We also have a problem that this particular nolock select sometimes return even less records than it should.I know it sounds impossible but it happens.So anyone who has experience with select with nolock, please share :)Thanks in advance, Yani
View 4 Replies View RelatedNOLOCK Or Not To NOLOCK
Mar 9, 2005I need some help to under stand when the right time is for NOLOCK. I work in a small dev group and NOLOCK seams to be a buzz word and others are throwing it in all over for no apparent reason.
I read the thing from http://www.sql-server-performance.com/ and I am sure that our web and SQL servers are about 100x over sized for the application. While are ASP.Net (VB) app may demonstrate some hesitation from time to time I am more inclined to blame poor VB.Net coding techniques before slow SQL. The point being the NOLOCK is being added to SELECTS that are not part of a transaction and were using the SQL data adapter to return datasets or single column values.
Also I am not even sure it’s being used correctly. The OLM has the example:
SELECT au_lname FROM authors WITH (NOLOCK)
However I am seeing it formatted like this:
SELECT au_lname FROM authors (NOLOCK)
I am by no mean an expert, I follow what I read in books or from examples from others. And I have never read in a book go crazy with NOLOCK because it’s the bomb!
Any thoughts? I am trying to learn as much as I can before I raise my hand and say this might be a bad idea.
Thanks
NOLOCk
Jan 29, 1999Other than "dirty" reads, what are the cons of using NOLOCK throughout a query?
View 1 Replies View RelatedDTS- WITH (NOLOCK)
Mar 7, 2001Hi,
I have a job that runs 3 seperate DTS packages.
The first step imports a file and runs successfully.
The second step which is the 2nd DTS package is hanging in the execute mode until I manually stop the job. Apparently,We discovered a bulk insert that is blocking a select statement--both proccesses are within this second DTS package. I tried using the WITH (UNLOCK) on the tables but this DTS package is still failing.
Does anyone have any suggestion? It would be greatly appreciated.
Db2, Nolock
Mar 4, 2004Hi guys,
I am a new user for DB2.
In DB2 V8, i have a table with some no of columns.
table test
col1
col2
col3
col4
Now i want to issue a query like this.
select col1 from test with(NOLOCK) where col1 = <some value>
when i am executing this query on that time i am getting a error message like this...
SQL0158N The number of columns specified for "MT.TEST" is not the
same as the number of columns in the result table. SQLSTATE=42811
Anyone can help me???
i tried to find out.
I did the same thing with SQL server 2000.
I am not facing any problem there.
Thanks & Regards,
Muthu
NOLOCK Help
Jun 6, 2006Paul Randal,
There has been a discussion/debate going on this thread about the benefits and drawbacks of using the NOLOCK hint:
http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=67294
It occurred to me that you might know more about this than any of us, or at least be able to point us to a white paper or knowledge base article that explains the subject in more detail. Any light you can shed on the subject would be a big help.
CODO ERGO SUM
With (nolock)
Jan 8, 2008
is really helpful use "with (nolock)" sentence in selects??
100% useful?? disadvantages?
best regards
Joseph
NOLOCK On Views
Jun 2, 1999Hello,
Does anyone know if you place NOLOCK after a view in a select statement, if the effects trickle down to the tables in the view? Or does one have to add NOLOCK to each table within the view?
Thanks
NOLOCK Sentence
Jun 23, 2004Hello !!
I'm using the sentence NOLOCK for selects, but I have many sentences, Is there any way to set a parameter in the DBMS, to use NOLOCK parameter by default ???? I mean, I don't like to lock any table for selects.
Is It possible ???? How to do It (step by step) ?
Thanks !!
NOLOCK On Views
Nov 1, 2005Hey guys,
I came across a SQL statement, thought up by a developer, in which two views were joined with the NOLOCK hint:
SELECT v1.xxx, v2.yyy
FROM dbo.vw_SomeView v1 WITH (NOLOCK)
INNER JOIN dbo.vw_SomeOtherView WITH (NOLOCK) ON v1.id = v2.id
The views are not created the NOLOCK hint. So my question is: has the NOLOCK hint any effect here?
I've looked in the BOL and searched on the net but can't find anything on this particular topic.
Lex
PS. Personally I don't like to use views in JOINs. I've seen too many cases in which tables are joined twice just because they are part of both views. Further more I don't like the "random" use of NOLOCK because most people don't seem to understand the implications of it. But this is besides the point of my question ;)
Still Getting Blocked Despite WITH (NOLOCK)
Apr 5, 2006I'm running a heavy SELECT query using WITH (NOLOCK). This still causes other processes trying to INSERT in one of the tables to get blocked.
I thought the locking hint would prevent from blocking other processes?
NOLOCK And No Resources?
Mar 31, 2008What will happen if I'm running a query with the NOLOCK hint but the SQL Server has run out of resources?
Thanks!
NOLOCK Option ?
May 12, 2008Hi,
I was sreading about NOLOCK that it could prevent deadlocks but could return data which is not committed yet.
1) Should we use NOLOCK with select statements
2) If the transaction isolation level is set appropriately (e.g. Serializable)in the component (for e.g COM+ component) but NOLOCK is specified in the select then would it return uncommitted data. I mean if the transaction is controlled at hihger level then what will be the Pros and Cons of using NOLOCK.
Thanks
What Is The Purpose Of Using WITH NOLOCK
Aug 12, 2013What is the purpose of using WITH(NOLOCK)?
View 3 Replies View RelatedNolock Problem
Dec 28, 2007Hi!
select * from rubberstock_tbl_shoppingcarttemp
It dosent take datas from the table but
select * from rubberstock_tbl_shoppingcarttemp (nolock)
This querey takes the data from the table
what can i do to retrieve records through first query.I dont know what
is happening please explain and also dont know about nolock
Thanks in advance!
NOLOCK Clarifications
Feb 25, 2008When the NOLOCK hint is included in a SELECT statement, no locks are taken when data is read. This gives a Dirty Read in a result set.
The data retrieved in the select statement may not be correct since some other process might have updated the data while it was taken in the select statement.
Now, Can I know what is the use of NOLOCK? In which way we can make efficient use of NOLOCK ???
Question About NOLOCK
Mar 30, 2008Hi,
I have never used NOLOCK, or ROWLOCK, or anything of that sort. It's something I thought was over my head when I first encountered it and as I am gaining a better grip on SQL I have decided I want to try and tackle it. Also, because I think its causing me some problems :)
I recently implemented a new query into my application.
The query below gets the COUNT(*) of certain tables. Some of these tables are tall (5 million plus rows)
The counts returned are not absolutely critical information, and we are not joining or doing any other transactions based on this data. I believe running these counts on these pretty active tables (selects,inserts) are possibly causing slowdowns ?
Would using NOLOCK be an appropriate situation for something like this ? I am looking for a performance increase hopefully, and hoping there isnt much of a downside? I'm also not sure what type of reliability to expect from NOLOCK.
Any help much appreciated !!
Thanks once again
mike123
create PROCEDURE [dbo].[select_UserStats_Admin_TEST]
(
@userID int
)
AS SET NOCOUNT ON
DECLARE @Mail_Sent INT, @Mail_Received INT, @Comments_Sent INT, @Comments_Received INT,
@friendsListCount INT
SELECT @Mail_Sent = count(*) FROM tblMessage WHERE messageFrom = @userID
SELECT @Mail_Received = count(*) FROM tblMessage WHERE messageTo = @userID
SELECT @Comments_Sent = count(*) FROM tblComment WHERE CommentFromID = @userID
SELECT @Comments_Received = count(*) FROM tblComment WHERE CommentTo = @userID
SELECT @friendsListCount = count(*) FROM tblFriends WHERE userID = @userID
SELECT @Mail_Sent as Mail_Sent, @Mail_Received as Mail_Received, @Comments_Sent as Comments_Sent,
@Comments_Received as Comments_Received, @friendsListCount as friendsListCount
With Nolock Problem
Feb 17, 2006Hi,Is there a way to catch every select comming to sql and change it toselect with nolock?or how to make database READ UNCOMMITTED permanent?any ideas?Richard
View 3 Replies View RelatedDeadlocks And Use Of Nolock
Jul 20, 2005I am getting lot of deadlocks in my application. As it is very complexti avoid deadlocks at this stage of application we have done few stepsto lessen the impact.We have added retries after deadlock is capturted.We have added select * from TABLE with (nolock) wherever possible.But interestingly second step is not working. I have few simple selectstatements where i am using nolock criteria still I am gettingdeadlock victim error. Any idead why it happening. I thought as soonas I put nolock in the query it will ignore all the locks.My sp isCREATE procedure sp_Check_denomination@supply_till_idint,@product_codechar(4),@iso_currency_codechar(3),@denominationmoneyasdeclare @product_id numeric(5)select @product_id = product_id from product with (nolock) whereproduct_code = @product_codeif exists (select *from transaction_inventory TI with (nolock),product_ccy_denom PCD with (nolock)where TI.supply_till_id = @supply_till_idand TI.product_id = @product_idand TI.iso_currency_code= @iso_currency_codeand TI.denomination = @denominationand TI.product_id = PCD.product_idand TI.iso_currency_code = PCD.iso_currency_codeand TI.denomination = PCD.denominationand PCD.product_id=@product_idand PCD.denomination = @denominationand PCD.iso_currency_code=@iso_currency_codeand PCD.tradeable = 1)beginreturn(1)endelsebeginreturn(0)endGO
View 1 Replies View RelatedWhen To Use The NOLOCK Hint.
Jul 20, 2005Background:I am currently working on a mission critical web based applicationthat is accessed 24 hours a day by users from just about every timezone. We use MS SQL Server as our database and we have lots ofproblems with time-outs. We used to have lots of problems with locksuntil my management decided that we would use the WITH (NOLOCK) hinton EVERY select statement and WITH (ROWLOCK) on EVERY updatestatement. I have argued since the beginning that the NOLOCK hintshould be the exception and not the rule. Meanwhile we continue tohave problems related to time-outs.Problem:I'm the one that they call when there are time-out errors.I am a programmer first and a DBA when I have to be. I'd really liketo hear from some of you who are the opposite. I realize that thereare many factors that contribute to slow response from a databaseserver (indexes, RAM, disk speed, etc.), but what I really need tohear from an expert is whether or not using NOLOCK on **EVERY** queryin a 30GB database that has 344 tables is a bad idea.Thanks in advance,Stephen McMahonJoin Bytes!
View 2 Replies View RelatedNOLOCK Deprecated?
Dec 5, 2007Is the NOLOCK optimizer hint being deprecated? Or does this apply only to use of NOLOCK in UPDATE and DELETE statements or what exactly?
I can see that in this article that there are circumstances in which the hint is deprecated; however, I have developers that are acting like NOLOCK is about to be dropped entirely. As far as I know, that is not the case but I would definitely like some feedback on this.
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 Hint On Views?
Nov 27, 2007Hi all
If i have a view:
CREATE VIEW vw_Users
AS
SELECT * FROM Users WITH(NOLOCK)
Is it suggested to use nolock in views?
And if i needed to use this view in stored procs is it then suggested to apply the nolock hint?
CREATE PROC [dbo] .[usp_GetCompanyUsers]
AS
SELECT * FROM Companies WITH(NOLOCK) JOIN
vw_Users WITH(NOLOCK) --<< ---is this suggested?
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 RelatedWrong Result Set When Using NoLock
Oct 22, 2007I have a Store Procedure on a Sql Server 2000 Where I use the Table Hint"NoLock" on all selects.One of my clients (OleDbConnection from C#) doesn't get the same Result Setas the others. The result Set should have 31 rows but this client only gets5!When I remove all the "NoLocks" everything works fine. How can that be?
View 5 Replies View RelatedInstallation Error - 'NOLOCK'
Jun 27, 2007I get the following error when installing SQL Server Express SP2 on Windows XP SP2 with all current updates. The only other thing installed is .NET 2.0. Does anyone know how to resolve the issue.
[Microsoft][SQL Native Client][SQL Server]Could not continue scan with NOLOCK due to data movement
Thanks,
Connection Level NOLOCK
Aug 2, 2007Hi!
when WITH (NOLOCK) statement is used in a select statement, it allows to retrieved data from a set of data locked by another transaction. Is it possible to enforce this at connection level?
I mean to open a connection using sqlclient and enforce NOLOCK so that all select statements post to database using that connection are not locked by other transactions.
thanks in advance
With Nolock In Sql Server Please Advice
Jan 27, 2008
I have read lots of article about with nolock, and have seen many projects using with nolock option.
Please advice me if i am right.
1.Normal select queries can use with no lock
2. Batch jobs should not use with no lock.
please guide me, am i right.
Thanks
Extensive Use Of NOLOCK, Any Issues?
Oct 20, 2007
I'm currently working on a system that makes a number of read queries whilst updates are taking place. Assuming that these reads don't need to be 100% accurate (i.e. they may incorrectly reflect partial updates) is there any other problem/danger from using WITH (NOLOCK)?
I'm aware of one specific NOLOCK bug but I wanted to see what the community thought.
Is There A Difference Between NOLOCK And READUNCOMMITTED?
Nov 5, 2007Hi All,
Just out of Curiosity, is there any difference between NoLock and ReadUncommitted? From my knowledge there is no differenece. But I am not sure.
Lookup Task With NOLOCK
Mar 2, 2006I have an SSIS package that unpivots data - each row from the source becomes 20-24 rows in the destination db. In the dataflow it looks up some type-data IDs before inserting into the destination table. The whole process flies through the data at an incredible rate, however I find that the final commit on data insertion takes a very long time, and two of the lookup tasks remain yellow throughout. It appears that there may be a contention issue because the final table has FKs to those lookup tables.
In T-SQL it is possible to do SELECT..... WITH (NOLOCK), but when I modified the SQL statement of the lookup task by adding this clause, it caused an error "Incorrect syntax near the keywork 'with'."
Is there any way around this problem? THNX!
PhilSky