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..
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.
Hi 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
I am trying to do a calculation where I show the [YesEmail] / [TotalCustomers]. It wont let me do it unless i do two queries. Is there a way to put this all in this select statment.
Code:
SELECT customer_lifetime_totals.occurrence_1_store_no as [StoreNo], COUNT( case when customer.email_address IS NULL then 1 end) as [NoEmail], COUNT( case when customer.email_address IS NOT NULL then 1 end) as [YesEmail], COUNT(customer.customer_no) AS [TotalNewCustomers]
FROM customer_lifetime_totals INNER JOIN customer ON customer_lifetime_totals.customer_id = customer.customer_id WHERE (occurrence_1_transaction_date > CONVERT(DATETIME, '2006-08-01 00:00:00', 102)) GROUP BY customer_lifetime_totals.occurrence_1_store_no ORDER BY customer_lifetime_totals.occurrence_1_store_no
This works ... but only when i put the previous query in a temp table and then run another query referring to it.
Code:
cast(100*(cast(YesEmail as float) / TotalNewCustomers) as numeric (5,2)) as [Percent]
I want to calculate the Total_Cost and get the result of the formula from SELECT Query. Following is the formula of Total_Cost. I have declared variables for formula. How I can create SELECT/RUN query successfully for mathematical calculation to calculate the Total_Cost.
--Formula of Total_Cost = [min (price, Pay1) x Interest1 + max (min (price - Pay1, Pay2), 0) x Interest2 + Max ((price - Pay2), 0) x Interest3, LMT]
declare @price numeric(18,7)=255550 declare @Pay1 numeric(18,7)=645500 declare @Pay2 numeric(18,7)=235000 declare @Interest1 numeric(18,7)=0.05500 declare @Interest2 numeric(18,7)=0.03533 declare @Interest3 numeric(18,7)=1.00000 declare @LMT numeric(18,7)=10000.00 Select [min (@price, @Pay1) x @Interest1 + max (min (@price - @Pay1, @Pay2), 0) x @Interest2 + Max ((@price - @Pay2), 0) x @Interest3, LMT] as Total_Cost
Now each table holds different measures e.g. 326, 229 & 278. I would like to subtract the measure_value of 229 from 278 and then add the measure_value from 278 from this. e.g
(326-229) + 278 = new measure_value.
This is for each id-product where the following 3 conditions meet:
the ID_PRODUCT, ID_MARKET AND ID_BUCKET match. Im lost, any help would be great.
thanks
Jay
p.s this what i have started with at the moment as a test however it dont work.
SELECT ID_PRODUCT, ID_MARKET, ID_BUCKET, ID_COLLECTION, ID_MEASURE, MEASURE_VALUE FROM (SELECT TOP 100 PERCENT dbo.DPOUT_EXCEPTIONS_326.ID_PRODUCT, dbo.DPOUT_EXCEPTIONS_326.ID_MARKET, dbo.DPOUT_EXCEPTIONS_326.ID_BUCKET, dbo.DPOUT_EXCEPTIONS_326.ID_COLLECTION, dbo.DPOUT_EXCEPTIONS_326.ID_MEASURE, dbo.DPOUT_EXCEPTIONS_326.MEASURE_VALUE + DBO.DPOUT_LSBP_229.MEASURE_VALUE as 'MEASURE_VALUE' FROM dbo.DPOUT_EXCEPTIONS_326 INNER JOIN dbo.dpout_lsbp_229 on dbo.dpout_exceptions_326.id_product = dbo.dpout_lsbp_229.id_product where dbo.DPOUT_EXCEPTIONS_326.ID_PRODUCT = dbo.dpout_lsbp_229.id_product and dbo.DPOUT_EXCEPTIONS_326.ID_MARKET = DBO.DPOUT_LSBP_229.ID_MARKET and dbo.DPOUT_EXCEPTIONS_326.ID_BUCKET = DBO.DPOUT_LSBP_229.ID_BUCKET)
We have an old ASP application that authenticates to a SQL Server 2000 database using the IUSER account.
We are exploring the possibility of moving it to a DMZ so users can access from home. The IUSER account is being used for all database activity for this application. Is there any reason to be concerned about using IUSER as opposed to sql authentication for this tool, or any other security risks I should be wary of. Mind you there may be some sensitive information contained in the database. Thanks in advance.
I am sertainly no SQL expert so I am looking for a bit of help(actually quite desperate).The extra CPU and 1GB of RAM to be added to a server (Compaq DL380 G2:1.4 GHz PIII with a Gig of RAM) have not come in and we are scheduledto go live tomorrow with a MS SQL Server web app. Will potentiallyinsufficient hardware resources endanger the data of other appsrunning on the SQL Server or will the system simply be slow foreveryone?Basically, I need to know whether SQl Server bogs down gracefully(under 2x-3x an acceptable load) or will we be corrupting the databasewith a crash.Thanks a million,Bert
Use the view master.sys.sql_logins (new in 2005) to get at the varbinary passwords like you did in your Sql Server 2000 scripts (instead of using passwords from master.dbo.sysxlogins).
I have altered the sp_help_revlogin (from Microsoft article # 246133 )
PLEASE TEST/FIX before you use this:
if exists (select * from dbo.sysobjects where id = object_id(N'[dbo].[sp_help_revlogin_2005]') and OBJECTPROPERTY(id, N'IsProcedure') = 1)
drop procedure [dbo].[sp_help_revlogin_2005]
GO
SET QUOTED_IDENTIFIER OFF
GO
SET ANSI_NULLS OFF
GO
CREATE PROCEDURE sp_help_revlogin_2005 @login_name sysname = NULL AS
DECLARE @name sysname
DECLARE @logintype char(1)
DECLARE @logindisabled int
DECLARE @binpwd varbinary (256)
DECLARE @txtpwd sysname
DECLARE @tmpstr varchar (256)
DECLARE @SID_varbinary varbinary(85)
DECLARE @SID_string varchar(256)
IF (@login_name IS NULL)
DECLARE login_curs CURSOR FOR
SELECT sid, name, type, is_disabled FROM master.sys.server_principals
WHERE name <> 'sa' and type in ('S','U','G')
ELSE
DECLARE login_curs CURSOR FOR
SELECT sid, name, type, is_disabled FROM master.sys.server_principals
WHERE name = @login_name
OPEN login_curs
FETCH NEXT FROM login_curs INTO @SID_varbinary, @name, @logintype, @logindisabled
I have created calcalated measures in a SQL Server 2012 SSAS multi dimensional model by creating empty measures in the cube and use scope statements to fill the calculation.
(so I can use measure security on calculations
as explained here )
SCOPE [Measures].[C];
THIS = IIF([B]=0,0,[Measures].[A]/[Measures].[B]);
I've read a bunch of articles saying you should always remove the guest user from the user databases and model. It seems to me that if a user only has public access then the user can't do anything on the database. If the guest user only has public access to a user database how is it a security threat? I must be missing something.
We are developing an application that requires change tracking.We tested it in development and test environments and we are preparing our production deployment.The very first thing that needs to be done is an
ALTER DATABASE [db_name] SET CHANGE_TRACKING = ON (CHANGE_RETENTION = 2 DAYS, AUTO_CLEANUP = ON)
We are holding on this first step because this statement alone executed for a good 4min on the development server. The production environment is many times larger and busier, and we can’t afford service disruption, so we are at the point where we need to understand what’s involved in running this ALTER DATABASE statement.Is there any documentation on what is happening behind the scene when this statement executes such that we can assess the risks of running it in production?
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.
