Hi Everybody,
One of my friend asked me "How do we reduce the query logical, scan reads
in SQL Server?".
I really don't know, how to answer him.
Can anybody explain me regarding this.
thanks,
Srini
Hello
I'm doing som performance research, I have a index with following priority: ClientId, Active, ProductId. Active is a bit field telling whether the Product is active or not, it can be inactive products than active, but always at least one active product.
When I'm executing
SELECT * FROM [table] WHERE ClientId = [id] AND ProductId IN (1,2,3,5,7,9,20)
I'm getting following result: Scan count 1, logical reads 490
When I'm leading SQL Server to the right paths by including the to possible values in Active by executing the following SQL:
SELECT * FROM [table] WHERE ClientId = [id] AND ProductId IN (1,2,3,5,7,9,20) AND Active IN (0,1)
I'm getting following results: Scan count 14, logical reads 123
With this information, which version would you say is fastest and why?
When I was running this query 1000 times with different ClientId I got a average time of 172 ms for the first query, and 155 ms for the second one. I have been told that scan count is very expensive... out of this example it seems that the cost of 1 scan count is like 20 logical reads?
How do I determine which method I should use ifI want to optimize the performance of a database.I took Northwind's database to run my example.My query is I want to retrieve the Employees' Firstand Last Names that sold between $100,000 and$200,000.First let me create a function that takes the EmployeeIDas the input parameter and returns the Employee'sFirst and Last name:CREATE FUNCTION dbo.GetEmployeeName(@EmployeeID INT)RETURNS VARCHAR(100)ASBEGINDECLARE @NAME VARCHAR(100)SELECT @NAME = FirstName + ' ' + LastNameFROM EmployeesWHERE EmployeeID = @EmployeeIDRETURN ISNULL(@NAME, '')ENDMy first method to run this:SELECT EmployeeID, dbo.GetEmployeeName(EmployeeID) ASEmployee, SUM(UnitPrice * Quantity) AS AmountFROM OrdersJOIN [Order Details] ON Orders.OrderID =[Order Details].OrderIDGROUP BY EmployeeID,dbo.GetEmployeeName(EmployeeID)HAVING SUM(UnitPrice * Quantity) BETWEEN100000 AND 200000It's running in 4 seconds time. And here are theStatistics IO and Time results:SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server parse and compile time:CPU time = 17 ms, elapsed time = 17 ms.(3 row(s) affected)Table 'Order Details'. Scan count 1, logical reads 10,physical reads 0, read-ahead reads 0.Table 'Orders'. Scan count 1, logical reads 21,physical reads 0, read-ahead reads 0.SQL Server Execution Times:CPU time = 3844 ms, elapsed time = 3934 ms.SQL Server Execution Times:CPU time = 3844 ms, elapsed time = 3935 ms.SQL Server Execution Times:CPU time = 3844 ms, elapsed time = 3935 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.Now my 2nd method:IF (SELECT OBJECT_ID('tempdb..#temp_Orders')) IS NOT NULLDROP TABLE #temp_OrdersGOSELECT EmployeeID, SUM(UnitPrice * Quantity) AS AmountINTO #temp_OrdersFROM OrdersJOIN [Order Details] ON Orders.OrderID =[Order Details].OrderIDGROUP BY EmployeeIDHAVING SUM(UnitPrice * Quantity) BETWEEN100000 AND 200000GOSELECT EmployeeID, dbo.GetEmployeeName(EmployeeID),AmountFROM #temp_OrdersGOIt's running in 0 seconds time. And here are the Statistics IOand Time results:SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 0 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.Table '#temp_Orders0000000000F1'. Scan count 0, logicalreads 1, physical reads 0, read-ahead reads 0.Table 'Order Details'. Scan count 830, logical reads 1672,physical reads 0, read-ahead reads 0.Table 'Orders'. Scan count 1, logical reads 3, physical reads 0,read-ahead reads 0.QL Server Execution Times:CPU time = 15 ms, elapsed time = 19 ms.(3 row(s) affected)SQL Server Execution Times:CPU time = 15 ms, elapsed time = 19 ms.SQL Server Execution Times:CPU time = 15 ms, elapsed time = 20 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 1 ms.(3 row(s) affected)Table '#temp_Orders0000000000F1'. Scan count 1,logical reads 2, physical reads 0, read-ahead reads 0.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 3 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 3 ms.SQL Server Execution Times:CPU time = 0 ms, elapsed time = 3 ms.SQL Server parse and compile time:CPU time = 0 ms, elapsed time = 0 ms.By the way why "SQL Server Execution Times"exists 3 times and not just one time?Summary:The first code is clean, 1 single SELECT statement buttakes 4 long seconds to execute. The logical reads arevery few compared to the second method.The second code is less clean and uses a temp table buttakes 0 second to execute. The logical reads are waytoo high compared to the first method.What am I supposed to conclude in this example?Which method should I use over the other and why?Are both methods good depending on which I prefer?If I can wait four seconds, it's better to reduce the logicalreads in order to provide less Blocking on the live tablesin a heavily accessed database?Which method should I choose on my own database?Calling a function like dbo.GetEmployeeName getsprocessed per each returned row, correct? That meansIf i had a scenario where 1000 records were to be returnedwould it be better to dump 1000 records to a temp tablevariable and then call a function to process each recordone at a time?Or would the direct approach without usinga temp table cause slower processing and moreblocking/deadlocks because I am calling the functionper each row as I am accessing directly from the tables?Thank you
View 1 Replies View Relatedwe had some slow down complaints lately and this query seems to be the culprit almost every single time. The estimated execution plan is a clustered index seek as there is a clustered index on the uidcustomerid column. setting profile statistics on shows that every time it executes it does an index seek.
profiler session showed a huge number of reads for these queries depending on the value being looked up. 1500 through 50000. i set up profile io on and the culprit is lob logical reads. everything else is 0 or very low. in this case lob logical reads is over 1700.
3 of the columns in the select statement are text columns. when i take them out of the query the lob logical reads drops to 0 and goes up incrementally as i add each column back in.
is there anyway to improve the performance without changing data types to varchar(max)?
select SID,Last_name,Name_2,First_name,Middle_initial,Descriptives,Telephone_number,mainline,Residence,ADL,
DID_number,Svce_street,Svce_town,Svce_state,Svce_appt,Mailing_street,Mailing_town,Mailing_state,Mailing_appt,
Mailing_zip,Listing,Addl_listing,Published,Listed,Gold_number,PIN,status,SSnumber,tax_jurisdiction,
Bill_date,Past_balance,Service_start_date,Service_end_date,LOA,FCC_type,Line_type,I_W,Jacks,Voice_messaging,
vms_ring_cycles,CCS,phonesmarts,ringmate,voice_dialing,Bill_detail,Contact_Number,Contact_extension,
Best_Time,suspend,suspend_start,suspend_end,credits_allowed,credits_granted,home_region,Calling_Plan,Local_Plan,
Local_Plan_Rate,Flat_Rate,Sales_agent,Community,Building_Mgmt,How_Heard,Incentive_1,Incentive_1a,Incentive_1b,
Incentive_1c,Incentive_2,Incentive_2a,Incentive_2b,Incentive_2c,Incentive_3,Incentive_3a,Incentive_3b,
Incentive_3c,block_operator,block_collect,block_group,block_adult,block_call_return,block_repeat_dialing,
block_call_trace,block_caller_id,block_anonymous,block_all_high_toll,block_regional_and_ld,block_DA_Call_Completion,
block_DA,block_3rd_party,bank,prepayment,dial_around_number,custid,waive_interest,Financial_Treatment,
Other_Feature_1_code,Other_Feature_1_rate,Other_Feature_2_code,Other_Feature_2_rate,Other_Feature_3_code,
Other_Feature_3_rate,Other_Feature_4_code,Other_Feature_4_rate,Partial_Account,mail_date,snp_1_date,snp_2_date,
terminate_date,snp1notified,snp1peak,snp1offpeak,snp2notified,snp2peak,snp2offpeak,avg_days_paid,Pulled_Ld,SNP1,
SNP2,Treatment,Collections,Installment,Nynex_BTN,LD_rate,local_discount,to_month,rounds_up,full_package_made,
local_made,PIC,LPIC,tax_exempt_local,tax_exempt_federal,CommissionedAgent,LDRateID,UidCustomerId,
accVchLineClassUSOC,block_Inter_Reg_LD,block_international,block_DA_3rd_Collect,block_DH2,block_ISP_2,block_ISP_3,
block_ISP4_3_GBAS,block_ISP3_3_GBAS,block_collect_only,block_LD_Reg_DA,block_usage_based,block_ISP5_3_GBAS,
block_ISP5_2_GBAS,block_group_adult,csr_PIC,csr_LPIC,csr_SA,csr_exception,cutover_status,cutover_datetime,
OutsideAgent,prfVchAttributes,uidResellerID,Category,uidDealID
from profiles where UidCustomerID in (352199267)
I have a table with 50% Logical Scan Fragmentation. [ according to Dbcc Showcontig (myTable) ]
Why after running DBCC INDEXDEFRAG (myDB,myTable) does it still sit at 50%.
Why isn't it lower?
Why is there often such a dramatic discrepancy between the logical reads recorded in the trace file versus the output of STATISTICS IO?
In the server-side trace I have running I found a reporting procedure that shows having 136,949,501 reads (yes, in hundreds of millions), and it's taking 13,508 seconds to complete.
So I pull the code from the trace and execute it via SSMS - it runs < 1 second, and only generates about 4,000 reads (using various different parameters I get the same result)
The execution plan shows nothing unusual
A table in one of my databases is running very slowly. The IO is very high and below is a printout from the SET STATISTICS IO ON command run on a common query used on the table:
(4162 row(s) affected)
Table 'WebProxyLog'. Scan count 3, logical reads 873660, physical reads 3493, read-ahead reads 505939, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
I have a clustered unique index and a nonclustered index on the table. I have ran SQL Profiler and opened the trace in Database Tuning Advisor, DTA displays 0% improvement suggestions. I have a number of statistics on the table and index which are all up to date and fragmentation is less than 1%. I've tried a number of variations on indexes to improve performance but to no avail. There is only one query which runs on the table, and the nonclustered index created on the table did significantly improve performance, however the query still runs at around 23 seconds. The query does bring back a large amount of data however i'm sure there is a way to bring down the IO and logical reads to improve performance.
The table and index scripts are below:
Code Snippet
-- =================== Table and Clustered index ===========================
CREATE TABLE [dbo].[WebProxyLog](
[ClientIP] [bigint] NULL,
[ClientUserName] [nvarchar](514) NULL,
[ClientAgent] [varchar](128) NULL,
[ClientAuthenticate] [smallint] NULL,
[logTime] [datetime] NULL,
[servername] [nvarchar](32) NULL,
[DestHost] [varchar](255) NULL,
[DestHostIP] [bigint] NULL,
[DestHostPort] [int] NULL,
[bytesrecvd] [bigint] NULL,
[bytessent] [bigint] NULL,
[protocol] [varchar](12) NULL,
[transport] [varchar](8) NULL,
[operation] [varchar](24) NULL,
[uri] [varchar](2048) NULL,
[mimetype] [varchar](32) NULL,
[objectsource] [smallint] NULL,
[rule] [nvarchar](128) NULL,
[SrcNetwork] [nvarchar](128) NULL,
[DstNetwork] [nvarchar](128) NULL,
[Action] [smallint] NULL,
[WebProxyLogid] [int] IDENTITY(1,1) NOT NULL,
CONSTRAINT [pk_webproxylog_webproxylogid] PRIMARY KEY CLUSTERED
(
[WebProxyLogid] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
-- =================== Nonclustered Index ===========================
CREATE NONCLUSTERED INDEX [dta_ix_WebProxyLog_Kaction_clientusername_logtime_uri_mimetype_webproxylogid] ON [dbo].[WebProxyLog]
(
[Action] ASC
)
INCLUDE ( [ClientUserName],
[logTime],
[uri],
[mimetype],
[WebProxyLogid]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
-- =================== Query which is called regularly on the table ===========================
SELECT [User] = CASE
WHEN LEFT(clientusername,3) = domain' THEN RIGHT(clientusername,LEN(clientusername) - 3)
ELSE clientusername
END,
logtime AS [Date],
desthost AS [Site],
uri AS [Actual Site]
FROM webproxylog
WHERE CONVERT(Datetime,CONVERT(VarChar(25),logtime,106),106) BETWEEN '20 apr 2008' AND '14 may 2008'
AND(RIGHT(uri,4) NOT IN('.css','.jpg','.gif','.png','.bmp','.vbs'))
AND (RIGHT(uri,3) NOT IN('.js'))
AND LEFT(mimetype,6) = 'text/h'
AND (uri NOT LIKE '%sometext.local%')
AND (uri NOT LIKE '%sometext.co.uk%')
AND [action] = 9
AND (clientusername IN ('USERNAME'))
ORDER BY logtime ASC;
PS There are 60,078,605 rows in the table
Please help!
Many Thanks
I am running a query in SQL 2000 SP4, Windows 2000 Serverthat is not being shared with any other users or any sqlconnections users. The db involves a lot of tables,JOINs, LEFT JOINs, UNIONS etc... Ok it's not a prettycode and my job is to make it better.But for now one thing I would like to understand with yourhelp is why the same SP on the same server and everythingthe same without me changing anything at all in terms ofSQL Server (configuration, code change, ...) runs inQuery Analyzer in 1:05 minute and i see one table get ahit of 15 million logical reads:Table 'TABLE1'. Scan count 2070, logical reads 15516368,physical reads 147, read-ahead reads 0.This 'TABLE1' has about 400,000 recordsThe second time i ran right after in Query Analyzer again:Table 'TABLE1'. Scan count 2070, logical reads 15516368,physical reads 0, read-ahead reads 0.I can see now the physical reads being 0 as it isunderstandable that SQL is now fetching the data frommemory.But now the third time I ran:Table 'TABLE1'. Scan count 28, logical reads 87784,physical reads 0, read-ahead reads 0.The Scan count went down from 2070 to 28. I don'tknow what the Scan count is actually. It scanned thetable 28 times?The logical reads went down to 87,784 reads from 15million and 2 seconds execution time!Anybody has any ideas why this number change?The problem is i tried various repeats of my test, irebooted the SQL Server, dropped the database, restoredit, ran the same exact query and it took 3-4-5 secondswith 87,784 reads vs 15 million.Why i don't see 15 million now?Well i kept working during the day and i happen to run intoanother set of seeing 15 million again. A few runs wouldkeep running at the paste of 15 million over 1 minute andeventually the numbers went back down to 87,784 and 2seconds.Is it my way of using the computer? Maybe i was openingtoo many applications, SQL was fighting for memory?Would that explain the 15 million reads?I went and changed my SQL Server to used a fixed memoryof 100 megs, restarted it and tested again the samequery but it continued to show 87,784 reads with 2 secondsexecution time.I opened all kinds of applications redid the same testand i was never able to see 15 million reads again.Can someone help me with suggestions on what could bethis problem and what if i could find a way to come tosee 15 million reads again?By the way with the limited info you have here about thedatabase I am using, is 87,784 reads a terrible number ofreads, average or normal when the max records in the manytables involved in this SP is 400,000 records?I am guessing it is a terrible number, am I correct?I would appreciate your help.Thank you
View 4 Replies View RelatedWe would like to benchmark our logical reads daily to show our improvement as we tune the queries over time.
I am using sys.dm_exec_query_stats summing the Physical and Logical Reads. Is this a viable option for gathering this metric? Is this a viable metric to gather?
select sum(total_physical_reads) as TotalPhyReads, sum(total_logical_reads) as TotalLogReads from sys.dm_exec_query_stats;
How best to provide performance based metrics.
How can I improve performance of my search if I am looking in a table with more than ten million rows with a "like query"?
Does putting an index mean only telling the computer to start in a particular order?
if I index all the coloums does my search get faster ?
how can I decide on an indexing strategy?
I am doing sp tuning. It has several lines. SO I divided into several small queries and executed individually and check the execution plans. In one small query, I found table scan is happening. That query is basically retrieving all columns from a table but the table doesn't have any pk or Indexes. So is it better to create non-clustered index to remove table sca.
View 2 Replies View RelatedHi Friends,
I have three tabels A,B,C having relation of primery & forign key, and i want to fetch data from all three.
In case if only A have the values and B & C dont have values, then also i want values.
But my simple sql statement dose not show any data, if B & C dont have values.
Any one tell me that how to fetch data from this type of Situation???????
pls
Thanks,
gs
Hi,
Te following situtation is :
ReportModel is created ,there is only a named query in DSV ,it has a few tables in it(The relationship are inner joins and outer joins).
The question is how could I create a unique logical primary key to identify each unique row in the named query dataset, and also you cannt generate a model unless the named query has a logical primary key . how can I solve this problem,any help?
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.????
Hi,
This is on Sybase but I'm guessing that the same situation would happen on SQL Server. (Please confirm if you know).
I'm looking at these new databases and I'm seeing code similar to this all over the place:
if not exists (select 1 from dbo.t1 where f1 = @p1)
begin
select @errno = @errno | 1
end
There's a unique clustered in dex on t1.f1.
The execution plan shows this for this statement:
FROM TABLE
dbo.t1
EXISTS TABLE : nested iteration.
Table Scan.
Forward scan.
Positioning at start of table.
It's not using my index!!!!!
It seems to be the case with EXISTS statements. Can anybody confirm?
I also hinted to use the index but it still didn't use it.
If the existence check really doesn't use the index, what's a good code alternative to this check?
I did this and it's working great but I wonder if there's a better alternative. I don't really like doing the SET ROWCOUNT 1 and then SET ROWCOUNT 0 thing. SELECT TOP 1 won't work on Sybase, :-(.
SET ROWCOUNT 1
SELECT @cnt = (SELECT 1 FROM dbo.t1 (index ix01)
WHERE f1 = @p1
)
SET ROWCOUNT 0
Appreciate your help.
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?
Hi!
I was assigned to solve performance problems for an application. I fired up Sql Server profiler and started a trace. Downloaded Sql Server Trace Analyzer. It's a trial version so it's very limited. What I found is that one stored procedure generates almost 400 000 reads everytime it's used and it's used everytime the user wants to see his orders. I've tried to translate the t-sql to english from swedish, it looks something like this:
select top 100
o.orderid,
o.name,
o.latestdeldate,
os.name as OrderStatus,
os.orderstatusID,
p.placeID,
p.name as place,
p.address,
p.city,
a.name as worktype,
noOfActions=(select count(*) from actions a where a.order_orderid=o.orderid),
noOfServiceObjects = (select count(*) from Serviceobject s, Actions a where s.Place_PlaceID = o.Place_PlaceID and a.order_orderid = o.orderid and a.Serviceobject_serviceobjectid = s.serviceobjectid),
...
...
...
It has 8 select count(*) in the select statement then in the where statement it has 2 more select count(*).
I know it's very difficult for you to come up with a solution but do you know a better way than to use select count(*) everywhere? The count is used for to show different status flags on the website.
/Magnus
Jesus saves. But Gretzky slaps in the rebound.
If I'm doing a dirty reads and a someone updates a record when I'm trying to read it is it possible to read both the old and new records thereby retrieving two records?
View 2 Replies View RelatedHow can You find the reads and writes per second of your hard drives in sql. I am reading my SQL book and it says that your average disk should have 125 or less i/o's. And it gave the forumal but as mentioned I don't know how to find the reads and writes.
View 4 Replies View Relatedserver: QAT on clustering server ----> 23 seconds
----------------------------------------------------
SS 2000 developer edition SP4
win NT 5.2 (3790) SP4
MeM 7935 MB
processors 4
root directory C:program files...
use a fixed memeroy size 640 MB
reserve physical memory for sql server
minimum query memory 1024 kb
use all available processors
minimum query plan threshold for considering 5
PROFILER READS = 5234
server: MILLER ----> 3 seconds
----------------------------------------------------
SS 2000 developer edition no service pack
win NT 5.2 (3790) SP4
MeM 2047 MB
processors 4
root directory f:MSSQL$INAQAT
dynamically configure sql server memory
use all available processors
minimum query plan threshold for considering 5
PROFILER READS = 598
----------------------------------------------------
Making story short. I got an application that hits only 1 database called RECORDS. I'm getting different duration when running an application. 23 and 3 seconds.
Same database, same objects and same application.
SERVER QAT is our staging server, means lots of databases
SERVER MILLER is just a server i just assembled, means just one database (RECORDS).
Not sure if it's because it's a clustering server that is causing the issue nor the reads. If its the reads, what is causing it? Do you think is the how the memory is configured?. Will the experts pls stand up?
So I€™m at a dead-end looking for the reason behind the following behavior. Just to make sure no one misses it, the 'behavior' is the difference in the number of reads between using sp_executesql and not.
The following statements are executed against a SQL 2000 database that contains >1,000,000 records in the act_item table. They are run using Query Analyzer and the Duration and Reads come from SQL Profiler
SQL 1:
exec sp_executesql N'update act_item set Priority = @Priority where activity_code = @activity_code', N'@activity_code nvarchar(40),@Priority int', @activity_code = N'46DF335F-68F7-493F-B55E-5F9BC6CEBC69', @Priority = 0
Reads: ~22000
Duraction: 250-350 ms
SQL 2:
DECLARE @Priority int
DECLARE @Activity_Code char(36)
SET @Priority = 0
SET @Activity_Code = '46DF335F-68F7-493F-B55E-5F9BC6CEBC69'
update act_item set Priority = @Priority where activity_code = @activity_code
Reads: ~160
Duration: 0 ms
Random information:
Activity_code is an indexed field on the table, although it is not the primary key. There are a total of four indexes on the table, none of which include the priority as one of the fields.
There are two triggers on the table, neither of which is executed for this SQL statement (there is an IF UPDATE(fieldname) surrounding the code in the trigger)
There are no foreign relationships
I checked (using perfmon) to see if a compilation/recompilation was happening. No it's not.
Any suggestions as to avenues that could be examined would be appreciated.
TIA
I write a work about database, and I want to write the diffrence between Table scan and Index scan. When is the index scan effectient? Use the database a Table scan when there is an index on the table or always a index scan when the index is nonselective? Can be a Table Scan effecient than a index scan?
Hello,
im using sqldatareader to read my data and whenever time i loop through the reader it starts from second row why is that?
here is my code:while (reader.Read()){hinfo.Name = reader["_name"].ToString();hi.Add(hinfo);}
i look at the database and i have two rows but its reading only the second row, skiping the first row
I have a set of triggers that log the history of changes to a table - i.e. I record inserts, updates, deletes (pretty standard audit stuff I suppose). I want to also log reads on that data. If I were using sprocs for reading data, this would be relatively painless, but I am using an O/R mapper to handle my data access, which writes dynamic sql at runtime (and I don't want to use sprocs with it) and then sends it down to the DB. Is there a way I can intercept reads and log them to the same table I am logging other actions? I know very little about the new capabilities of SQL Server 2005, but I would think I could somehow, maybe via the new CLR capabilities or similar, get access to these types of events within the database? Anyone? I know I could always do this higher up in the application layers, but I would like to keep all of this at the database level if possible....Thanks,
View 1 Replies View RelatedSQL 6.5 - 5.5 Gig
NT
Hello,
Throughout the day our Document Management application generates high busts of physical page reads when users query the database.
What SQL configuration parameter(s) should I check/modify to insure that the database is performing at it's optimun during these bursts?
Thank You in advance.
Is there a way to get a total count of all SELECT, UPDATE, DELETE and INSERT statements to a SQL Server 6.5 database during a 12 hour period? I'm thinking maybe someone knows of a software that reads the log or monitors the server... I've been looking at the performance monitor and, although it has good information, it doesn't capture DML's.
FYI - it's for capacity planning.
TIA,
Mike
I'm trying to insert all the rows from a table to a new table.
(insert A select * from AA)
The reads on Profiler shows ar really high value (10253548).
First I created a unique clustered index and the reads shows (3258445), then I created a non clustered index expecting to have lower reads. Instead the reads shows (10253548).
I read creating indexes helps reduce reads. But it's not happening.
Any ideas what is going on?
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GUys,
Is there any way track tables which have most no of reads and writes from a database of 400 tables.
Thanks
Hi,
Can any of can explain, what the "Reads" column in Profiler exactly mean ? I'm not comfortable with the explanation given in BOL.
"The number of read operations on the logical disk that are performed by the server on behalf of the event. These read operations include all reads from tables and buffers during the statement's execution"
For the same procedure with same parameters, if the server is not loaded much, the Reads are in a few hundreds, but when there are more than 1000 concurrent users, why it is going to millions ? What other parameters affecting this reads ? And how can I reduce it ?
Environment: SQL Server 2005 64-bit Enterprise Edition on Windows Server 2003 R2 Server x64 Enterprise Edition SP2
Thanks in Advance.
Regards
Babu
Hi,
I have been seeing a basic scenario of a write transaction appearing to unexpectedly lock-out reading.
The database has isolation set to "READ COMMITTED".
The scenario is:
1.) Start a transaction (for doing a write)
2.) Do a read before the transaction (for doing the write) is committed (e.g. sqlCommand2.ExecuteReader()).
--> the code will appear to lock-up (then time out).
I see the same behavior if I step through the "write" code with the debugger (to a point after the transaction is started, but before it is committed), and run a "SELECT * FROM" type query from Microsoft SqlServer Management Studio.
Following is the code sample demonstates the issue.
Thoughts on how to resolve the issue (to let me do "read committed" reading of the database table)?
Thanks!
Andy
Module Transaction
Sub Main()
Dim exception1 As Exception
Try
' Create/Open Database Connection
Dim sqlConnection1 As New System.Data.SqlClient.SqlConnection("Server=GRB-AB;Database=Transaction;Trusted_Connection=True;")
sqlConnection1.Open()
' Start transaction
Dim sqlTransaction1 As System.Data.SqlClient.SqlTransaction = sqlConnection1.BeginTransaction()
' Set Parent record
Dim sqlCommand1 As New System.Data.SqlClient.SqlCommand("INSERT INTO Parent (Name) VALUES ('ParentValue');", sqlConnection1)
sqlCommand1.Transaction = sqlTransaction1
sqlCommand1.ExecuteNonQuery()
' Get Id from parent record (note: this code assumes the table was empty when this program starts)
sqlCommand1 = New System.Data.SqlClient.SqlCommand("SELECT Id FROM Parent;", sqlConnection1)
sqlCommand1.Transaction = sqlTransaction1
Dim parentId As Integer = CType(sqlCommand1.ExecuteScalar(), Integer)
'
' Do reading test to test concurrently reading table being written to
'
' Create/Open Database Connection for reading test
Dim sqlConnection2 As New System.Data.SqlClient.SqlConnection("Server=GRB-AB;Database=Transaction;Trusted_Connection=True;")
sqlConnection2.Open()
Dim sqlCommand2 As New System.Data.SqlClient.SqlCommand("SELECT Id FROM Parent;", sqlConnection2)
sqlCommand2.ExecuteReader()
Dim i As Integer
While (sqlCommand2.ExecuteReader.Read = True) ' <===== LOCKS UP HERE **************
i = i + 1
End While
'
' End reading test
'
' Set child record
sqlCommand1 = New System.Data.SqlClient.SqlCommand( _
"INSERT INTO Child (Name, ParentId) VALUES ('ChildValue', " & parentId.ToString & ");", sqlConnection1)
sqlCommand1.Transaction = sqlTransaction1
sqlCommand1.ExecuteScalar()
' Either 1.) commit transaction OR 2.) rollback transaction
Dim test As Boolean = False
If test = False Then
sqlTransaction1.Commit()
Else
sqlTransaction1.Rollback()
End If
sqlConnection1.Close()
sqlConnection2.Close()
Catch ex As Exception
exception1 = ex
End Try
End Sub
End Module
I have written a same stored proc in TSQL and SQL CLR which basically takes an input xml and returns xml document. In SQL Profiler, I am getting reads value about five times more for the CLR. Does anyone has any idea why the CLR is doing more reads than TSQL? Thanks in advance.
View 5 Replies View RelatedI am having problems w/ the indexes on a particular table. Currently the scan density if 25%. I have ran the dbcc dbreindex and the scan density does not improve. I have manually dropped and recreated all of the indexes on the table (there are only two) and still no help.
I have a clustered Primary Key index on my part_number and project_number fields and another index on the project_number field. If I drop the second index and only have my primary key index, it still doesn't help. The fill factor was originally set to 90% and I changed this to 30%, 20%, 10%, 0% and the best scan density I could acheive was 50%.
The data in this table is not updated that often, on average about 15 records a day are updated, and there are only 107 records. This is a small table, but there is a possibility for it to grow rapidly and I want to be prepared now.
Does anyone have any ideas or suggestions? I've tried everything I can think of with no luck.
TIA,
Chris