Does With (nolock) Absolutely Guarantee No Locks Are Taken?
May 10, 2006
I need to run a few short-running queries against a production system. I need to be absolutely certain that SS doesn't take out any locks on the table as a result.
Does "with (nolock)" absolutely guarantee this? I've read BOL on the topic and I understand isolation level read-uncommitted. But I want to validate that there's not any undocumented behavior in SS that might violate the documentation (which clearly states that no shared locks are issued).
I've got an INSERT that's selecting data from a linked server and attempting to push 10 million rows into the blank table. More or less, it looks like this:
The instance of the SQL Server Database Engine cannot obtain a LOCK resource at this time. Rerun your statement when there are fewer active users. Ask the database administrator to check the lock and memory configuration for this instance, or to check for long-running transactions. There are no other active users. I ran it again and monitored the following DMO to watch the growth of locks for that spid:
SELECT request_session_id, COUNT (*) num_locks -- select * FROM sys.dm_tran_locks --where request_session_id = 77 GROUP BY request_session_id ORDER BY count (*) DESC
The number of locks started small and held for a while around 4-7 locks, but at about 5 minutes in the number of locks held by that spid grew dramatically to more than 8 million before finally erroring again with the same message. Researching, I can't figure out why it's not escalating from row locks to table locks at the appropriate threshold. The threshold in was set to 0 at first (Server Properties > Advanced > Parallelism > Locks). I set it to 5000, and it still didn't seem to work. Rewriting the INSERT to include a WITH (TABLOCK) allows it to finish successfully in testing. My problem is that it's coming out of an ETL with source code that I can't edit. I need to figure out how to force it to escalate to locking the entire table via table or server level settings.
A colleague suggested that installing service packs may take care of it (the client is running SQL Server 2008 R2 (RTM)), but I haven't found anything online to support that theory.
We are migrating our database(s) from ORACLE to SQL. In Oracle we were able to issue a SELECT statement and see all of the locks (Blocking and Non-Blocking) currently in the system. The query also included the Process ID of the process we needed to kill in order to get rid of the lock.
We now need to create the same type of query for Microsoft SQL Server 2012. I have seen postings on different sites saying that this info can be obtained using SP_WHO2 or using the SQL Server Management Studio Activity Monitor's PROCESSES tab, but we are looking for a SELECT statement that will give us similar information.
In my application, I need to be able to guarantee that processing for a re-used conversation is completed prior to starting processing the next (re-used) conversation. My application is based on the concepts from the sample posted on Remus's blog: http://blogs.msdn.com/remusrusanu/archive/2007/05/02/recycling-conversations.aspx#comments). Essentially (in this sample), we create a new conversation for each SPID and re-use the conversation, so that messages are sent through the queue (and processed in order) for each SPID. SPID was used in the sample code as an example of some application-specific "thing" that you care about message ordering for. To prevent a conversation from living forever (using up log/resources), they are ended after 1 hour using DialogTimer and a customer message type.
My conundrum is this:
Assume conversation 1 (on SPID 1) is flooded with a large number of messages just before the conversation timer expires. The DialogTimer then expires before the target queue is drained. The sample code (mentioned above) then creates a new conversation for the same SPID (with a DialogTimer of 1 hour). Until the queue for conversation1 is drained, we have 2 conversations being processed for the same SPID. This same problem would occur in any application where you re-use conversations for a period of time (using DialogTimer), and then start a new conversation when the DialogTimer expires.
So although I like having the idea fof being able to re-use conversations, I would need to guarantee that conversation 1 is finished processing before conversation 2 starts processing (for the same SPID, to be consistent with the sample above). If I could get these 2 conversations into the same conversation group on the target queue, the CG locking would solve the problem. But because conversation groups only apply to the initiator queue (when you begin dialog with related conversation), I have no "out of the box" way to control how the conversation groups are associated on the target queue. Remus posted an idea here (bottom of thread): http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=182646&SiteID=1, which was to just send a special message at the beginning of each new conversation (containing the conversation group to use), and then doing a move conversation to conversationgroupid on the target queue. I've tried this solution, and the problem is 1.) if the set convo message fails for some reason, the conversation group is not set and 2.) if the target queue seems to reject most of my move conversation commands with the error "The destination conversation group '<conversation guid>' is invalid." - which I am guessing is due to the fact that this convo group id is being used on the initiator as well.
We have an app that threads together emails coming out of Exchange, using their messageid. To ensure threading works correctly, we need to ensure uniqueness of messageid, which we do with a unique index (we also need to be able to lookup by messageid when a message comes in).
We are currently porting the app from Oracle and PostgreSQL to SQL Server and are having problems with the 900 byte max length of an index. The problem is that the maximum size of a messageid (according to the Exchange docs) is 1877 bytes.
Relative newb to SSRS here, but the answer to this question evades me; answers and insight are appreciated.
Report in question is an invoice form. It requires an absolutely bottom-of-page aligned footer that has databound elements.
This is so that whatever page that footer finally appears on will print in such a way that the address will align in a windowed envelope.
Ironically, Books Online gives this exact scenario in explaining headers and footers in SSRS, but they cleverly don't explain how an absolutely bottom-of-page-aligned and data-bound footer can be made to happen. Headers at absolute page top is obviously no problem. Footers at page bottom, not so much.
So, this is not a "page footer"--page footers are employed in the body. Also this footer is databound, so a page footer as it's known in SSRS is out the window anyway.
Most of the time this will print on a single page, but if it breaks to multiple pages, that footer needs to go all the way to the absolute bottom.
I grasp that the "report footer" for SSRS is just what appears at the end of any repeating controls that you've implemented in your body. Because SSRS uses this kind of repeating-control based idiom rather than a section-based idiom as Crystal does, this kind of (what I would consider very basic) positioning control is looking fairly impossible right now.
Among what I've tried:
--Page footer (can't; databound)
--Specifying a page break after the pre-footer controls, and/or a page break before the controls that make up the footer in their properties. This leads to unpredictable results with blank printed pages (as many as 8 for what previews as a 2-page report, how silly is that?).
--Putting in a page-height rectangle as part of the footer (with and without the page breaks mentioned above), with the idea of forcing a basically blank page at the end of the report so that the footer will go to the bottom. SSRS will go ahead and break the page anyway on long elements like that, which again leads to the "footer" being printed in the middle or top of the final page, or whereever it happens to fall.
I may be having to explain to my client that you can't get there from here, and they may have to redesign their report. Does anyone have any insight?
Report in question is an invoice form. It requires an absolutely bottom-of-page aligned footer that has databound elements. This is so that whatever page that footer finally appears on will print in such a way that the address will align in a windowed envelope. Ironically, Books Online gives this exact scenario in explaining headers and footers in SSRS, but they cleverly don't explain how an absolutely bottom-of-page-aligned and data-bound footer can be made to happen. Headers at absolute page top is obviously no problem. Footers at page bottom, not so much.So, this is not a "page footer"--page footers are employed in the body. Also this footer is databound, so a page footer as it's known in SSRS is out the window anyway.
Most of the time this will print on a single page, but if it breaks to multiple pages, that footer needs to go all the way to the absolute bottom.I grasp that the "report footer" for SSRS is just what appears at the end of any repeating controls that you've implemented in your body. Because SSRS uses this kind of repeating-control based idiom rather than a section-based idiom as Crystal does, this kind of (what I would consider very basic) positioning control is looking fairly impossible right now.Among what I've tried:
--Page footer (can't; databound) --Specifying a page break after the pre-footer controls, and/or a page break before the controls that make up the footer in their properties. This leads to unpredictable results with blank printed pages (as many as 8 for what previews as a 2-page report, how silly is that?). --Putting in a page-height rectangle as part of the footer (with and without the page breaks mentioned above), with the idea of forcing a basically blank page at the end of the report so that the footer will go to the bottom. SSRS will go ahead and break the page anyway on long elements like that, which again leads to the "footer" being printed in the middle or top of the final page, or whereever it happens to fall.
I may be having to explain to my client that you can't get there from here, and they may have to redesign their report.
ID varchar (contains alphanumeric values,not unique) Territory (combined with ID unique) Total_Used int can be null Date_ date (date of the import of the data) ID Territory Total_Used Date_ ACASC CAL071287 2014-06-01 ACASC CAL071287 2014-08-01 ACASC CAL071288 2014-09-01
[Code] .....
Now the problem,per month I need the most recent value so I'm expecting
I 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.
Hi, 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.
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.
Hello, 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?
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.
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 ;)
I'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?
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.
When 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 ???
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
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
Hi,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
I 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
Background: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!
Is 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.
I 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.
Hi 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?
Is 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
I 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?
