An interesting discussion yesterday. One of the programmers asked about the use of the NOLOCK optimizer hint with an iterator table aka table of numbers. His comment was that this optimizer hint was not efficient. Rather than give a knee-jerk response I thought it would be better to ask. The main circumstance is that the iterator table is completely static with a fill factor of 100%. My purpose is to eliminate lock contention if I can.
Are there reasons to not use the NOLOCK hint in this case to potentially improve performance?
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!
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?
I try do some tests and I get one doubt, why the optimizer don€™t make a constant scan in normal tables, for instance:
Code Snippet --drop table #tmp create table #tmp (id Int Identity(1,1) Primary key, name VarChar(250)) go insert into #tmp(name) values(NEWID()) insert into #tmp(name) values(NEWID()) go set statistics profile on go -- Execution plan create a Constant Scan select * from #tmp where id = 1 and id = 5 go set statistics profile off
GO
--drop table tmp create table tmp (id Int Identity(1,1) Primary key, name VarChar(250)) go insert into tmp(name) values(NEWID()) insert into tmp(name) values(NEWID())
go set statistics profile on -- Why execution plan does not create a Constant Scan for this case? select * from tmp where id = 1 and id = 5 go set statistics profile off
Is possible to use like hint with subselect? , i mean i want to find all rows in table A that contains a word in a field(CALLED CONTENT) in table B, concretely in a field called content too, i show you the idea although the syntax is incorrect.
select ' + char (39) + @country + char (39) + ' as PAIS, A.ID, A.IDUSUARIO MSISDN, NULL AS MSISDN_COD, convert(char(19),A.FECHA_ALVENTO, 121) AS FECHA_MO_LOCAL, NULL AS FECHA_MO_LOCAL_D,
I have a SQL command which I run on two separate servers. Both servers and configured and built the same. On server 1 it takes mere seconds, but on server 2 it takes over 5 minutes.
I have checked the execution plan on both servers and they are completely different. I ran UPDATE STATISTICS WITH FULLSCAN on both servers, but the execution plans were still different.
My question is why are the execution plans so different and how do I get them to execute with the same plan.
I tried this:use northwindgoSELECT OrderDateFROM Orders WHERE OrderDate > '19950101'see the query plan? okSELECT OrderDate, EmployeeIdFROM Orders WHERE OrderDate > '19950101'see the query plan? what appened?the only way to make an index seek instead of an index scan is toforce theindex usage ( with(index=orderdate) ), but I don't like this solutionalso try this:SELECT *FROM Orders WHERE employeeId > 9andSELECT *FROM Orders WHERE employeeId > 8Can someone explain why this appens? and how can I overturn theperformance loss problem (well not in orders table, but in my tablethere are 300K records and making a scan to retrieve 50 records is notexactly what I want)thanks to all
Is possible to use like hint with subselect? , i mean i want to find all rows in table A that contains a word in a field(CALLED CONTENT) in table B, concretely in a field called content too, i show you the idea although the syntax is incorrect.
select ' + char (39) + @country + char (39) + ' as PAIS, A.ID, A.IDUSUARIO MSISDN, NULL AS MSISDN_COD, convert(char(19),A.FECHA_ALVENTO, 121) AS FECHA_MO_LOCAL, NULL AS FECHA_MO_LOCAL_D,
Hi All,I have a question about lock hint for you :If the first user currently run a select commandwith share lock and hold it. What kind oflock (lock hint) should be used by the second userin the select command (from the same table) so thatthis command will wait until the first user releasesthe lock ?I have tried using tablock, tablockx, xlock andupdlock hint in the select command for the seconduser, but it is not successful. Below is myunsuccessful test :The first user :Begin Transactionselect fprefix from ut1 where fprefix = '000'The second user :select * from ut1 with (tablockx)Please help meThanks in advanceAnita Hery*** Sent via Developersdex http://www.developersdex.com ***Don't just participate in USENET...get rewarded for it!
Can I use the NO Lock hint when running a SELECT against a view that points to another server? Will the no lock "travel" to the other server through the view?
I'm looking for an in depth book, article, faq, whatever, regarding the query optimizer...
I've read the books online pretty thoroughly and have been sql coding for a number of years. The system I work on relies heavily on real time access to data and the number crunching procedures we use are a critical part of the design. For the most part, sometimes through trial and error, I have been able to find ways to achieve the performance we need, but I'm often surprised by the methods that prove most effective.
For example, I have cases where I can only get the performance I'm looking for using table functions, and other cases where indexed temporary tables are the only way. I have statements that run fast as a select statement, but when converted to an update statement limp along, forcing me to resort to cursors, temp tables, or table hints with varying degrees of success.
I'm wondering if anyone has come across material that takes an in depth look at the various technologies available and how to tweek queries. I want to get away from hours of testing and hacking.
Way back when, and at least in version 7 IIRC, the query optimizer gaveup when the where clause in a statement contained more than 4 searchconditions.Does anyone know if such a limitation still exist in MS SQL 2005? TheBOL seems to be silent on the issue.Boa
I'm very puzzled by the choice of NC index being made by the optimizerin this example. I don't actually think it should use an NC index atall.I have:Table: CustomerStatus_TSingle data page19 recordsClustered Index on CustomerStatusID:CREATE TABLE [CustomerStatus_T] ([CustomerStatusID] [int] NOT NULL ,[Name] [varchar] (50) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,[Description] [varchar] (200) COLLATE SQL_Latin1_General_CP1_CI_ASNULL ,[Code] [varchar] (30) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,[CodeAlt] [varchar] (30) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,[Ordinal] [int] NULL ,[Default] [int] NULL ,[Display] [bit] NOT NULL ,[StatusType] [varchar] (1) COLLATE SQL_Latin1_General_CP1_CI_AS NULL,[DateCreated] [smalldatetime] NULL ,[DateUpdated] [smalldatetime] NULL ,[DateArchived] [smalldatetime] NULL ,CONSTRAINT [PK_ROMS_CustomerStatus] PRIMARY KEY CLUSTERED([CustomerStatusID]) ON [PRIMARY]) ON [PRIMARY]If I run the following query, it does exactly what I expect and scansthe clustered index:SELECT customerStatusID, [Name] FROM CustomerStatus_TWHERE dateArchived IS NULLAND Display = 1AND StatusType = 'Q‘and gives the following QEP and IO statistics:|--Clustered Index Scan(OBJECT:([Reach_Roms].[dbo].[CustomerStatus_T].[PK_ROMS_CustomerStatus]),WHERE:(([CustomerStatus_T].[DateArchived]=NULL AND[CustomerStatus_T].[StatusType]='Q') ANDConvert([CustomerStatus_T].[Display])=1))Table 'CustomerStatus_T'. Scan count 1, logical reads 2, physicalreads 0,read-ahead reads 0.If I now put a NC index on the statustype column:create index ix_nci_statustype on customerstatus_t(statustype)the query plan changes to:SELECT customerStatusID, [Name] FROM CustomerStatus_TWHERE dateArchived IS NULLAND Display = 1AND StatusType = 'Q‘|--Filter(WHERE:([CustomerStatus_T].[DateArchived]=NULL ANDConvert([CustomerStatus_T].[Display])=1))|--Bookmark Lookup(BOOKMARK:([Bmk1000]),OBJECT:([Reach_Roms].[dbo].[CustomerStatus_T]))|--IndexSeek(OBJECT:([Reach_Roms].[dbo].[CustomerStatus_T].[ix_nci_statustype]),S EEK:([CustomerStatus_T].[StatusType]='Q') ORDEREDFORWARD)Table 'CustomerStatus_T'. Scan count 1, logical reads 7,physical reads 0, read-ahead reads 0.For some bizarre reason, the optimizer thinks that a NC index lookupon a single-page table, which ultimately costs 7 IOs, is cheaper thana table (or Clustered Index) scan of a single page. Why? Theshowplan cost also shows that it expects the NC index to be cheaper(which is presumably why it goes and uses it), but even after runningUPDATE STATISTICS on the table it still chooses the same idiotic queryplan.Any thoughts, or has anyone seen similar behaviour before, and cananyone please explain it to me?p.s. I don't actually WANT to put a NC index on this table, but Inoticed the behaviour by accident which is why I'm asking the question:-)
I need to get back the actual characters (without trailing blanks) contained in a char(43) field. So i tried: - substring(fieldname,1,len(fieldname)) which yields a 43 char column - using a variable that contains the actual length in substring(fieldname,1,@nchar)) the same. - tricking by concatenating the resulting string with a dummy like "" didn't work either. So apparently I am at a dead end. Anybody a clue, hint or solution???? Thanks to all contributors
Is it possible to place an exclusive row lock when running a SELECT query by using a lock hint (or otherwise).
Basically, when a select statement is run against a table I don't won't any other users to read that row until it has been updated - at some later stage.
Any suggestions on whether this is possible would be welcome.
I want to implement the following pattern (pseudo-code follows):
[for index in x different databases, where x is rather big]
create database MyDatabase_#{index}_Temp launch a dedicated ssis package on this database if I detect no error, proudly rename MyDatabase_#{index}_Temp to MyDatabase_#{index}_Last_Known_Good (drop the last_known_good first if it exist)
Later on, a consolidation process collect the data in Last_Known_Good versions of the databases.
My question: what is the simpliest way to achieve the rename operation (step 3) ?
I have tried an "alter database #{old_database_name} modify name = #{new_database_name}", but it works only once: once renamed, the database keeps the old mdf and ldf filenames, and the next create database will choke on this.
I have also tried to rename the logical filenames with ALTER DATABASE XXX MODIFY FILE (NAME = YYY, NEWNAME = ZZZ) but it doesn't work either.
I'd like to avoid specifying absolute mdf and ldf filenames myself, is it possible ?
Is there a DMV or similar in SQL 2012, or SQL 2008, that shows when a statistic was last used by the optimizer? I would like to cleanup some of the auto-generated stats, assuming it's possible to do so. In particular I'm looking to drop those statistics that were created by one-off queries, data loads, etc, and are now doing nothing but adding to the execution time of Update Statistics jobs.
declare @ContactId as integerset @ContactId = 5select *from Person.Contactwhere ContactId = @ContactIdOR @ContactId = -1If you run this in SQL 2005 on the AdventureWorks database,why the logical reads is 561Table 'Contact'. Scan count 1, logical reads 56and not 2 when you run without the second OR condition:declare @ContactId as integerset @ContactId = 5select *from Person.Contactwhere ContactId = @ContactIdHow can i use the same SP and either get one record returnedby passing the ID of the field, or pass a dummy parameter like-1 in order to get ALL the records returned.In this case even when i pass a parameter like ContactID = 5there is still a table scan (clustered index scan in this case)happening for the other OR condition.There's no method to tell SQL to start checking the first conditionwhether or not it is true then if it is false then check the second ORconditon. On the same topic does this mean all OR conditions areALWAYS verified regardless if one of them has already been determinedto be True?Thank you
Guys,what I need is a tool which gives details on the choice of anexecution plan by the SQL Server. For example, the cost for a hashjoin might be 200 and 100 for a nested loop, and therefore a nestedloop is used. Same thing for the access paths for each table/viewinvolved. In Oracle, we turn on event 100053 to see this kind of info.ThanxDaniel
I am trying to resolve performance issues in a third party application. I have run the profiler and found a transaction that performs a table scan against a 6 million row table. This transaction occurs repeatedly, so I thought, just add an index on the columns in the where clause used here. After adding the index, I looked at the estimated execution plan in Query analyzer, and I find that it is still performing the table scan. If I run the query it takes over 60 seconds to run, if i add an index hint, it runs in under a second. I ran DBCC SHOW_STATISTICS to see if the statistics were up to date:
Statistics for INDEX 'IX_Finish_dept'. Updated Rows Rows Sampled Steps Density Average key length -------------------- -------------------- -------------------- ------ ------------------------ ------------------------ Jun 26 2007 5:18PM 6832336 6832336 150 2.1415579E-7 18.0
(1 row(s) affected)
All density Average Length Columns ------------------------ ------------------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 2.1875491E-7 8.0 finish 1.9796084E-7 18.0 finish, dept
Hello All, I have a series of Stored Procedure that has a query taking a join of 5 tables. These tables are quiet large with couple of them having around 10 million rows. As this is a DSS application having periodic data loads, I thought of creating Indexed View on top of these tables. Now the problem is that the Indexed View is not directly used by the optimizer. I need to change my queries and put a WITH (NOEXPAND) query hint to make sure the indexed views are used. This is inspite getting dramatic improvement in the query timings (from 64 secs down to 3 secs) after using the Indexed Views. I would like to know what can be the possible reason for the optimizer not using the Indexed View by itself. Is it because my Indexed View caters to multiple queries or I am missing out on something basic.
My God! What happens if I miss a step, or put it in a different order??? I know I can specify ORDER BY StepID, but what about a missing step? I do have "missing ranges" script, but posting questions filtered through the script process may become a full-time job in itself...What to do, what to do...
