If you display the execution plan and run the following:
SET STATISTICS IO ON
go
SELECT ProductID, SupplierID
FROM Products
WHERE SupplierID = 1
I don't understand how come there is no
Bookmark Lookup operation happening to get the
ProductID?
I only see an Index Seek happening on SupplierID.
There is no composite index SupplierID + ProductID
so what am I not understanding here?
Thank you
I have query with an expensive Key Lookup on a joined table. The predicate is the column that I'm joining on, and the output list contains two columns from the joined table.
I've created a basic non-clustered index covering the predicate column and include-ing the two output columns. However, the execution plan ignores this, and insists on using the primary key of the joined table to do the expensive key lookup. I've tried adding the included columns to the index directly and there's no change. I've also tried running dbcc freeproccache and no change.
please explain the differences btween this logical & phisicall operations that we can see therir graphical icons in execution plan tab in Management Studio
thank you in advance
how to eliminate a key lookup from the execution plan
SET TRANSACTION ISOLATION LEVEL READ COMMITTED
SET NOCOUNT ON
SELECT COUNT(ph.lid) AS Total
FROM PLB ph
WHERE ph.lPhysician = @Physician
AND ph.BSF = CAST(0 AS bit)
[code]....
I'm in the process of trying to optimize a stored procedure with many queries. The execution plan provides a missing non-clustered index on nearly every query, and they're all fairly similar. The only real difference between them are what's in the INCLUDE statement. The two key columns are listed in every missing index. Let's say each query is approximately 5% of the total batch and 90% of the queries all fall into the category I listed above. How should I go about creating the missing indexes? Create all of the missing indexes or create one generic one that has all the INCLUDE columns? Create a minimal index with just a few of the common INCLUDE columns?
Here's an example of what I'm talking about with the missing indexes:
/*
USE [DB]
GO
CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>]
ON [dbo].[TABLE_1] ([COLUMN_A],[COLUMN_B])
INCLUDE ([C4ABCD],[C4ARTX],[C4ASTX],[C4ADNB],[C4AFNB],[C4BKVA])
GO
*/
/*
The Query Processor estimates that implementing the following index could improve the query cost by 99.9044%.
*/
/*
USE [DB]
GO
CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>]
ON [dbo].[TABLE_1] ([COLUMN_A],[COLUMN_B])
INCLUDE ([C4ARTX],[C4ASTX],[C4ADNB],[C4CZST])
GO
*/
/*
The Query Processor estimates that implementing the following index could improve the query cost by 99.5418%.
*/
/*
USE [DB]
GO
CREATE NONCLUSTERED INDEX [<Name of Missing Index, sysname,>]
ON [dbo].[TABLE_1] ([COLUMN_A],[COLUMN_B])
INCLUDE ([C4ABCD],[C4ARTX],[C4ASTX],[C4ADNB],[C4AFNB],[C4BKVA])
GO
*/
I run a query
select col1, col2, col3, col4
from Table
where col2=5
order by col1
I have a primary key on the column.The execution plan showing the clustered index scan cost 30% & sort cost 70%..When I run the query I got missing index hint on col2 with 95% impact.So I created the non clustered index on col2.The total executed time decreased by around 80ms but I didn't see any Index name that is using in the execution plan.After creating the index also I am seeing same execution plan
The execution plan showing the clustered index scan cost 30% & sort cost 70% but I can see the total time is reducing & Logical reads on that table is reducing.I am sure that index is useful but why there is no change in the execution plan?
execution plan of procedure shows
bookmark lookup cost : 46%
any way to reduce it ?
Thanks
alex
The benefit of the actual execution plan is that you can see the actual number of rows passing through each step - compared to the estimated number of rows.But what about the "cost percentages" ?I believe I've read somewhere that these percentages is still just an estimate and is not based on the real execution.Does anyone know this and preferable have a link to something that documents it?Thanks
View 1 Replies View RelatedWhen a nonunique nonclustered index is built on top of a clusteredindex, is it guaranteed that the bookmark in the nonclustered indexwill be kept in the same order as the clustered index?Here's an example to demonstrate my question:CREATE TABLE indextest (col1 int NOT NULL,col2 int NOT NULL,col3int,col4 int)ALTER TABLE indextest ADD PRIMARY KEY CLUSTERED (col1,col2)CREATE INDEX ix_indextest ON indextest (col1,col3)GOINSERT indextest VALUES (1,2,1,1)INSERT indextest VALUES (1,3,2,1)INSERT indextest VALUES (1,4,2,1)INSERT indextest VALUES (2,1,1,1)INSERT indextest VALUES (1,1,1,1)SELECT col1,col2 FROM indextest WHERE col1=1 AND col3=1DROP TABLE indextestThe select statement above is covered by the nonclustered index, sothat index is used. However, the nonclustered index is defined only toensure the ordering of col1 and col3 within the index; col1 and col2follow within the index as the bookmark to the clustered index. When Irun this query, my desired result is to have the records appear in theorder supported by the clustered index:1,11,2As it happens, the result I got was indeed in that order, but I don'tknow if it was mere coincidence, or if the bookmark in the nonclusteredindex is maintained in the same order as the clustered index. If Iwant to ensure the above order, is it sufficient to have thenonclustered index defined as above, or do I need to define it as:create index ix_indextest on indextest (col1,col3,col2)just to be sure that the results are returned in ascending order forcol1,col2? If the two-column index is sufficient, is it guaranteed tostill be sufficient in SQL2005 and future versions of SQL Server, or amI better off adding the third column just to be safe?Thank you,--Dennis Culley
View 4 Replies View RelatedI have a really strange problem.
I execute this query:
declare @cid int
set @cid = 2003227
select * from sales s, product p where p.product_Id = s.product_Id and customer_id = @cid
select * from sales s, product p where p.product_Id = s.product_Id and customer_id = @cid or @cid = 0
3 Million rows in sales, 120000 in product.
The first does and index seek, the second an index scan.
The execution plan reports that the scan takes 99.87% of the cost, and the seek takes 0.13%
This problem obviously gets worse the bigger the dataset / query /etc.
The reason I query this, is because it never used to take this long to do index scans. Is there something i can change, something i can fix?
Any help would be appreciated.
Josh
Hi,
Can I use index seek and still keep 'like' 'or' functionality for the following statement?
--prepare test table
create table entity (Id int identity(1,1), FamName varchar(200), LastName varchar(200))
go
create clustered index entity_id on entity (id)
go
create nonclustered index entity_lastName on entity (lastName)
go
insert into entity select famName,FirstName from table
--test index
declare @LastName varchar(10)
set @LastName = 'a'
select FamName
from entity
where @LastName is null or LastName like @LastName --clustered index scan
I have created a nolock view off a table to prevent locks. I have users coming in through MS Access that have switched their queries to run against the views. Now we are noticing that queries that used to run as a clustered index seek against the table are running as a clustered index scan against the table and performance in the queries has dropped.
Is there any way that the same query that hits the view instead of the table can be made to run faster or at least use the index seek?
Thanks,
Steve
the query:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WHERE a.AssociationGuid IN (
SELECT ada.DataAssociationGuid FROM AssociationDataAssociation ada
WHERE ada.AssociationGuid = '568B40AD-5133-4237-9F3C-F8EA9D472662')
takes 30-60 seconds to run on my machine, due to a clustered index scan on our an index on asset [about half a million rows]. For this particular association less than 50 rows are returned.
expanding the inner select into a list of guids the query runs instantly:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WHERE a.AssociationGuid IN (
'0F9C1654-9FAC-45FC-9997-5EBDAD21A4B4',
'52C616C0-C4C5-45F4-B691-7FA83462CA34',
'C95A6669-D6D1-460A-BC2F-C0F6756A234D')
It runs instantly because of doing a clustered index seek [on the same index as the previous query] instead of a scan. The index in question IX_Asset_AssociationGuid is a nonclustered index on Asset.AssociationGuid.
The tables involved:
Asset, represents an asset. Primary key is AssetGuid, there is an index/FK on Asset.AssociationGuid. The asset table has 28 columns or so...
Association, kind of like a place, associations exist in a tree where one association can contain any number of child associations. Each association has a ParentAssociationGuid pointing to its parent. Only leaf associations contain assets.
AssociationDataAssociation, a table consisting of two columns, AssociationGuid, DataAssociationGuid. This is a table used to quickly find leaf associations [DataAssociationGuid] beneath a particular association [AssociationGuid]. In the above case the inner select () returns 3 rows.
I'd include .sqlplan files or screenshots, but I don't see a way to attach them.
I understand I can specify to use the index manually [and this also runs instantly], but for such a simple query it is peculiar it is necesscary. This is the query with the index specified manually:
SELECT a.AssetGuid, a.Name, a.LocationGuid
FROM Asset a WITH (INDEX (IX_Asset_AssociationGuid)) WHERE
a.AssociationGuid IN (
SELECT ada.DataAssociationGuid FROM AssociationDataAssociation ada
WHERE ada.AssociationGuid = '568B40AD-5133-4237-9F3C-F8EA9D472662')
To repeat/clarify my question, why might this not be doing a clustered index seek with the first query?
create table t1(a varchar(50) , b varchar(50))
create index i1 on t1(a)
create index i2 on t1(b)
create view v1
as
select * from t1 where isnull(a,b) = 'test'
select * from v1
The above SQL "select * from v1" is doing a table scan.
What do I do to make it perform an index seek ????
TIA
- ForXLDB
Hey,
what is the difference between Table Scan und Index Scan?
I find no difitions in the internet
Finchen
Hi,
I want to know wht is a
TABLE SCAN
INDEX SCAN
INDEX SEEKand When they are used, Wht is the difference between all these.????
I'm new to SQL server but familiar enough with databases to know this doesn't seem right.
Here's the situation:
I have a table with real estate property information. There are about 650,000 rows in it. I have a nonclustered non-unique index on the city where the property is located. There are about 40 unique values in this index.
I do a simple query like:
SELECT city,address from propinfo where city= 'CARLSBAD'. The query will return about 4,000 rows. The problem is that the execution plan that it chooses is to do a full table scan. I.E. Even though there is an index on City, it chooses to look through 650,000 rows rather than do an index seek. Something sounds inefficient here. BTW, this happens in both SQL 7 and SQL 2000. Can anyone explain why this happens? I've got to think that SQL Server is more efficient here.
Hello, I have been looking at the execution plan for a procedure call and the select, compute scalar, stream aggregates, constant scan, nested loops, asserts are all at 0% cost, the PK costs are 2% apart from a rogue 7% and a few 20%, tables scans are all at 23%. The query cost realtive to the batch is 100%. What does this all mean?
I have put non-clustered indexes on all the table attributes that are involved in the select statements but this has made no difference, i am guessing this is because my tables are not heavily populated and i may have seen a difference if i had thousands of entries in the tables the select statements acted on, is this assumption correct?
Does anyone else bother using the execution plan to tweak there DB or is it a negligible tool?
Jill
In sql server 2005 management studio where do I find the option to run the sql query in the query analyser and also show the execution plan?
At present I see the option under Query menu which is "Display estimated Execution plan" which only shows the plan but does not execute the query.
Thanks
Does anyone know of a good way to copy the execution plan when using "Include Actual Execution Plan"?
I often need to copy this and mail it.
I know I can use PrintScreen button, but I need a more efficient way to do this.
If I just could rightclick the execution plan and select "Copy" and get complete plan it would be great.
Mladen?
E 12°55'05.25"
N 56°04'39.16"
Which of the following does NOT cause the execution plan of a query to berecompiled ?- new column is added to a table accessed by a query OR- index used by a query has been dropped from the database OR- query perfoms a join to return data from multiple tables OR- significant amount of data in a table has been mofified
View 1 Replies View RelatedHi,I have a table-valued user defined function (UDF) my_fnc.The execution of statement "select * from my_fnc" takes much longertime than runnig the code inside my_fnc (with necessary changes).What can be the reason?How can I see an execution plan used for UDF?Thanks a lotMartin
View 1 Replies View RelatedHi,I want to access the real execution plan via my webapplication after I have executed an SQL statement. I know how to get the estimated execution plan:1 cmd.CommandText = "SET SHOWPLAN_XML ON";2 cmd.ExecuteNonQuery();3 4 cmd.CommandText = myStatement;5 SqlDataReader dataReader = cmd.ExecuteReader();6 7 String plan = String.Empty;8 9 while (dataReader.Read()) {10 plan += dataReader.GetSqlString(0).ToString();11 }12 13 cmd.CommandText = "SET SHOWPLAN_XML OFF";14 cmd.ExecuteNonQuery();I want do compare the estimated costs with the real costs of the same statement. If I change code line 1 an 13 to "SET STATISTICS XML [ON|OFF]" the string "plan" will contain the result of the submitted SELECT statement, but I just need to get the plan and not the result itself. Thanks in Advance,Dominik
View 6 Replies View RelatedWhat does 'tablename. index... cost: 100%' mean when I use display estimated execution plan?
View 1 Replies View RelatedHello ,
I wanted to know whether we have an execution plan enabled in SQL 6.5 as we have it in SQL 7.0 and SQL 2000 .
I.e when we execute a query and if we enable ' show execution plan 'then it creates a map and shows the vital statistics .
If that is available on SQL 6.5 then i am missing that tool .
How can i have it installed on my SQL 6.5 server ??
Thanks.
Hi,
I want to know how to analyze query execution plan for complex queries and what information is useful from that for improving the performance. I have gone through details in some sites like www.like sql-performance.com (http://www.sql-server-performance.com/query_execution_plan_analysis.asp), where it was more generic. I want more info regarding this.
Can any one tell about the resources for this or do you have any white papers or documents, which you can share with me.
Thanks in advance,
sekhar
Hi ,
when
operator = then index SEEK
operator <> then index SCAN
Is normal ?
Example
SELECT *
FROM dbo.Batch
WHERE (Status = 'Batch Completed')
(1 row(s) affected)
StmtText
---------------------------------------------------------------------------------------------------------------------------------
|--Bookmark Lookup(BOOKMARK:([Bmk1000]), OBJECT:([PriceAvisPr].[dbo].[Batch]))
|--Index Seek(OBJECT:([PriceAvisPr].[dbo].[Batch].[IX_Batch]), SEEK:([Batch].[Status]='Batch Completed') ORDERED FORWARD)
StmtText
---------------------------------------------------------------------------------
SELECT *
FROM dbo.Batch
WHERE (Status <> 'Batch Completed')
(1 row(s) affected)
StmtText
------------------------------------------------------------------------------------------------------------------------
|--Clustered Index Scan(OBJECT:([PriceAvisPr].[dbo].[Batch].[PK_Batch]), WHERE:([Batch].[Status]<>'Batch Completed'))
Hi all,
I am experiencing performance problems with one of my stored procedures. When the stored procedure is first compiled an executed, it behaves as expected (it usually takes 1 or 2 seconds to complete). But its performace it is degradated, so in 1 day, it usually takes 120 seconds to complete !!!. Once the stored procedure is compiled, its performance it is then the expected.
It is a complex stored procedure with two integer parameters with only one select, but composed by multiple views and sub-queries. We have been trying to break the query into small pieces using temporary tables but without success. The SQL Profiler shows an unusual number of reads when it goes wrong (more than a million reads).
I think the problem is in the execution plan. I know than compiling the stored procedure, the problem is fixed, but I do not know exactly when and why it starts to happen.
The stored procedure is running under the following configuration:
- Microsoft SQL Server Standard Edition (64-bit).
- Version: 9.00.1399.06
- RAM 16 MB
- 8 CPUs
Anyone has any ideas or possible solutions?
Thanks in advance,
Carlos.
The cost of query with usage of functions is as same as that of withoutfunctionsIn the below code, the query cost of insert is 0.02% and two selectstatements costs same 0.04%Declare @t table(mydate datetime)Declare @i intset @i=1while @i<=5000Begininsert into @t values(getdate())set @i=@i+1EndSelect mydate from @tSelect convert(varchar,mydate,112) from @tBut I thought usage of convert function will take more query costWhat do you think of this?Madhivanan
View 5 Replies View RelatedWe've got as slightly unusual scenario happening whereby a statement ispassed to SQL which consists of two parts.BEGIN TRANSACTIONDELETE * FROM WhateverBULK INSERT INTO Whatever...(etc)COMMIT TRANSACTIONThe first is a deletion of the data and the second is the bulk insertof replacement data into that table. The error that we see is aviolation of the primary key (composite).The violation only happens if we run both processes together. If we runone, then the other, it works fine. If we set a line by line insert, itworks fine.My suspicion is that the execution plan that is being run is mostlikely working the two parts in parallel and that the records stillexist at the point that the insert is happening. Truncate is not anoption. The bulk insert was added for performance reasons. There is anoption of trying the bulk insert, and if that fails, do the line byline insert, but it's far from ideal.I think we can probably wrap this into two individual transactionswithin the one statement as follows :BEGIN TRANSACTIONDELETE * FROM WhateverCOMMIT TRANSACTIONBEGIN TRANSACTIONBULK INSERT INTO Whatever...(etc)COMMIT TRANSACTIONWill this give sufficient hint to SQL about the order it processes itso that it completes as we intend and not as it sees being the mostefficient method ?Or, is there a better approach to this ?I've seen that some hints can be passed to SQL for optimizing, but myunderstanding was that it was always better to trust the optimiser andre-work the query as needed.With the server having two processors, is it feasible that one is doingone part and the other processor the other part in parallel ? Willtelling it to use a single processor be worthwhile looking at ? MAXDOP1 ?Finally, I'd imagine that the insert is quicker to process than thedeletion. Is this correct ?ThanksRyan
View 14 Replies View RelatedUsing SQL Server 2000 SP4.There is a relatively complex stored procedure that usually completes inless than 20 seconds. Occasionally it times out after 180 seconds. The SPis called via ADO 2.8, using adCmdStoredProc command type. If I useProfiler to capture the EXEC that ADO sends to run the procedure, and runthat from QA, the procedure completes in less than 20 seconds as it should.The procedure is created WITH RECOMPILE. One additional twist is thatsp_setapprole is called from the client before running the procedure inquestion. This may be irrelevant, because even if I include the samesp_setapprole call when running the procedure from QA, it still executesquickly, and even if I comment out the call to sp_setapprole in the clientcode, the proc still times out when run from the client.The only thing that fixes it, at least for a day or two, is DBCCFREEPROCCACHE. So it appears that a bad plan is somehow stuck in memory andis only used when the procedure is called from the client app, and is notflushed even though the procedure was created WITH RECOMPILE.Other than scheduling the DBCC call to run every night, is there anythingelse I could try to get this resolved? Thanks.--(remove a 9 to reply by email)
View 5 Replies View RelatedI was hoping someone could shed some light on wierd situation i'm experiencing. I have the following query:
select count(*) LeadCount
from auto_leads al
where received > dbo.GetDay(GetDate())
dbo.GetDay simply returns a smalldatetime value of today's date.
Now I recently got thrown into a data mess and for some reason this query takes 8 seconds to run. Now the first thing I did was update the stats on the Received column of this auto_leads table. I re-run the query and I'm still getting 8 seconds. I look at the execution plan I can make figure out why this is happening.
I then change the above query so the filter received > dbo.GetDay(GetDate()) is now just received > '5/31/2006' and the query comes back immediately. This doesn't make sense to me because the GetDay function is really simple and comes back immediately. I then try the following query to confirm it isn't a problem with the GetDay function:
declare @Today DateTime
set @Today = dbo.getday(GetDate())
select count(*) leads
from auto_leads al
join type_lead_status tls on (tls.type_lead_status_id = al.type_lead_status_id)
where received > @Today
Sure enough, the query came back immediately. Next thing to go through my mind is that the query execution plan has been cached by SQL Server using the execution plan from before I updated the stats on the received column. So I executed sp_recompile 'auto_leads' and tryed the original query again. Still taking 8-10 seconds to come back.
So my question, is why when I remove the GetDay function call in my query filter is the query slow, as opposed to me just passing a variable into the query? Thanks!
- James
I'm new to sql server 2005 and was reviewing the execution plan on one of my queries.
I have a query that selects about 62,000 rows from a table of about 20 million
I see there is a index seek indicated but further down the execution plan I see that a large percent is being assigned to a RID LOOKUP on the same table.
Should I be concerned with this and if so, what would you recommend I do to correct it?