SQL 2012 :: How To Determine When A Statistic Was Last Used By The Optimizer
Aug 25, 2015
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.
I've got this query that runs in 30 seconds and returns about 24000. The table variable returns about 145 rows (no performance issue here), and the TransactionTbl table has 14.2 Million rows, a compound, clustered primary key, and 6 non-clustered indexes, none of which meet the needs of the query.
Actual execution plan shows SQL is doing an index seek, then a nested loop join, and then fetching the remaining data from the TransactionTbl using a Key Lookup.
I designed a new indexes based on the query, which when I force it's usage via an index hint, reduces the run time to sub-second, but without the index hint the SQL optimiser won't use the new index, which looks like this:
CREATE INDEX IX_Test on GLSchemB.TransactionTbl (CltID, Date) include (Ledger_Code, Amount, CurrencyID, AssetID)and I tried this: CREATE INDEX IX_Test on GLSchemB.TransactionTbl (CltID, Date, Ledger_Code, CurrencyID, AssetID) include (Amount)and even a full covering index!
I did some testing, including disabling all indexes but the PK, and the optimiser tells me I've got a missing index and recommends I create one EXACTLY like the one I designed, but when I put my one back it doesn't use it.
I though this may be due to fragmentation and/or stats being out of date, so I rebuilt the PK and my index, and the optimiser started using my index, doing an index seek and running sub-second. Thinking I had solved the problem I rebuilt all the indexes, testing after each one, and my index was used BUT as soon as I flushed the related query plan, the optimiser went back to using a less optimal index, with a seek and key lookup plan and taking 30 seconds.
For now I've resorted to using the OPTION (TABLE HINT(G, INDEX(IX_Test))) to force this, but it's a work around only. Why the optimiser would select a less optimal query plan?
I must determine FILEGROUP on my DB in SQL Server. Because when i wants to retrieve files which is stored in db, it would be face with error about FILEGROUP.
i must determin FILEGROUP on my DB in SQL Server. because when i wants to retrieve files which is stored in db, it would be face with error about FILEGROUP.
I am working on Sql Server 2012. and I have multiple databases there. Out of those, i want to move one of my databases to other SQL server 2012, For that i was trying to get approximate size of my database on current server. As i don't have the admin rights, so i can't get that. Can i get the approximate size by right clicking on database and by using the size property Under Database category to get the size idea?
Is there a way to determine when the SSAS Service last restarted? preferably a [mdx] query like you can do with the DB engine using a T-SQL query but any method that does not going to the servers OS and checking would be fine.
I can find many examples of loading DBCC results into tables. They all begin with a create table statement defining the results. My question is , other than trial and error, is there a way to determine what data types will be returned. Sure you can say that first element looks like an integer, but is it really a bigint, and that text string can be varchar(max) but will char(2) work.
I'm not looking for an answer for a specific DBCC function, but rather a generic way I can determine the characteristics of any DBCC result set.
I tried
SELECT * INTO #tmp FROM OPENROWSET('SQLOLEDB', 'Server=ray;Trusted_Connection=Yes;Database=Ed_sandbox', 'Set FmtOnly OFF; DBCC loginfo WITH tableresults ')
but I got back
Msg 11527, Level 16, State 1, Procedure sp_describe_first_result_set, Line 1
The metadata could not be determined because statement 'DBCC loginfo WITH tableresults' does not support metadata discovery.
Has anyone implemented or knows an easy refernce to implement F-statistic for single variable linear regression? I was told it's not implemented in SSAS, so it seems like implementing it manually is the only way to go.
Hi, Is there possibility to get somehow statistic for mostly used SPs in the SQL Server 2000 Database? Any field in sysobjects for number of executions for certian SP?
We are having an occasional problem occur where a process will not stop blocking.
We are trying to trace the problem, but in the interim, I would like to set up an alert that notifies me when a process has been blocking for too long.
Are any of the lock wait times good statistics to use for such an alert? If not, is there anything else I could look at from the alert level?
If I had to, I could periodically create a table of sysprocess spids that are at the top of blocking chains, then test for a spid that lingers. I'm hoping I can avoid this and use the built-in monitoring instead, though.
I'm moving data from one database to another (INSERT INTO ... SELECT ... FROM ....) and am encountering this error:
Msg 8114, Level 16, State 5, Line 6 Error converting data type varchar to numeric.
My problem is that Line 6 is:
set @brn_pk = '0D4BDE66347C440F'
so that is obviously not the problem and my query has almost 200 columns. I can go through one by one and compare what column is int in my destination table and what is varchar in my source tables, but that could take quite a while. How I can work out what column is causing the problem?
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
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
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:-)
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.