Stealth Indexes & Statistics Recompute
Jul 26, 1999
After our upgrade and migration from v6.5 to v7.0, there are new indexes shown on the sysindexes table. All of these new indexes have names that start with the characters '_WA_Sys_'.
Before the upgrade, one database had 88 indexes but now it has 643. One table went from 1 index to 92.
The systems person who did the install and upgrade believes that these new objects only appear to be indexes, and that they are statistics that are automatically generated to aid in performance.
a) Does anyone else have these?
b) What are they?
c) Where can I read about them?
d) Could they cause performance slowdown?
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Jan 20, 2006
We are inserting huge amount of data (could be several millions) during a fact upload. Therefore after the upload we recomputed the statistics. In oracle this can be done using the following sql statement:
analyze table <table_name> compute statistics
Do you know if there is any equivalent statement in SQL*Server? it has to run via JDBC like a SQL statement.
Thanks.
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Jul 13, 2007
I'm looking into the automatic recompilation of stored procedures andI have been reading up on the "Do not recompute statistics" option onindexes.Am I correct in concluding that disabling the "Do not recomputestatistics" option for an index, will ensure that no automaticrecompilations will occur as a result of updates to data in thatindex?Am I also correct in understanding that the "Update Statistics" willstill update statistics for the index even if the "Do not recomputestatistics" option is disabled?RegardsBjørn
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Jun 29, 2000
I am using the Maintencance Plan wizard, but it only allows me to either select the "reorganize data and indexes" option or the "update statistics" option (in the Optimizations tab). I can't select both of them. What is the reason for this?
joe
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Sep 1, 2000
Hi everyone,
I know that statistics called _WA_... are created on tables when auto create statistics is set on a database. Is this an indication that queries against the table would perform better if indexes were created on the columns in question? (The tables I'm interested in optimising are used equally for transactional querying and reporting)
Thanks for any replies!
Les
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Jul 15, 2015
I have a series of indexes that are showing as statistics. Is it because they are filtered or are defined as constraints?
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Nov 5, 2015
If I rebuild some indexes that are above 30% of average fragmentation, should I after that update statistics?
Also, How can I see if I Need to update statistics^on the tables of my database?
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Jul 20, 2005
Hello group.I have an issue, which has bothered me for a while now:I'm wondering why the column statistics, which SQL Server wants me tocreate, if I turn off auto-created statistics, are so important to theoptimizer?Example: from Northwind (with auto create stats off), I do the following:SELECT * FROM Customers WHERE Country = 'Sweden'My query plan show a clustered index scan, which is expected - no indexexists for Country. BUT, the query plan also shows, that the optimizer ismissing a statistic on Country, which tells me, that the optimizer wouldbenefit from knowing this.I cannot see why? (and I've been trying for a while now).If I create the missing statistics, nothing happens in the query plan (andwhy should it?). I could understand it, if the optimizer suggested an indexon Country - this would make sense, but if creating the missing index, queryanalyzer creates the statistics with an empty index, which seems to me to beless than usable.I've been thinking long and hard about this, but haven't been able to reacha conclusion :) It has some relevance to my work, because allowing theoptimizer to create missing statistics limits my options for designingindexes (e.g. covering) for some rather wide tables, so I'm thinking why notturn it off altogether. But I would like to know the consequences - hopesomebody has already delved into this, and knows a good explanation.RgdsJesper
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Aug 1, 2006
What is the unit of the numbers you get in the Time Statistics-part when running a query in Microsoft SQL Server Management Studio with Client Statistics turned on?
Currently I get mostly 0´s, but if I try and *** up a query on purpose I can get
it up to around 30... Is it milliseconds or som made up number based on clockcycles or... ?
I would also like to know if it´s possible to change the precision.
- Nikolaj
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Jul 1, 2014
I'm working to improve performance on a database I've inherited, and there are several thousand indexes. I've got a list of ones which should definitely exist within the database, and I'm looking to strip out all the others and start fresh, though this list is still quite large (1000 or so).
Is there a way I can remove all the indexes that are not in my list without too much trouble? I.e. without having to manually go through them all individually. The list is currently in a csv file.
I'm looking to either automate the removal of indexes not in the list, or possibly to generate the Create statements for the indexes on the list and simply remove all indexes and then run these statements.
As an aside, when trying to list all indexes in the database, I've found various scripts to do this, but found they all seem to produce differing results. What is the best script to list all indexes?
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Sep 18, 2007
So I'm reading http://www.sql-server-performance.com/tips/clustered_indexes_p2.aspx and I come across this:
When selecting a column to base your clustered index on, try to avoid columns that are frequently updated. Every time that a column used for a clustered index is modified, all of the non-clustered indexes must also be updated, creating additional overhead. [6.5, 7.0, 2000, 2005] Updated 3-5-2004
Does this mean if I have say a table called Item with a clustered index on a column in it called itemaddeddate, and several non-clustered indexes associated with that table, that if a record gets modified and it's itemaddeddate value changes, that ALL my indexes on that table will get rebuilt? Or is it referring to the table structure changing?
If so does this "pseudocode" example also cause this to occur:
sqlstring="select * from item where itemid=12345"
rs.open sqlstring, etc, etc, etc
rs.Fields("ItemName")="My New Item Name"
rs.Fields("ItemPrice")=1.00
rs.Update
Note I didn't explicitly change the value of rs.fields("ItemAddedDate")...does rs.Fields("ItemAddedDate")=rs.Fields("ItemAddedDate") occur implicitly, which would force the rebuild of all the non-clustered indexes?
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Jun 25, 2015
I have a requirement to only rebuild the Clustered Indexes in the table ignoring the non clustered indexes as those are taken care of by the Clustered indexes.
In order to do that, I have taken the records based on the fragmentation %.
But unable to come up with a logic to only consider rebuilding the clustered indexes in the table.
create table #fragmentation
(
FragIndexId BigInt Identity(1,1),
--IDENTITY(int, 1, 1) AS FragIndexId,
DBNAME nvarchar(4000),
TableName nvarchar(4000),
[Code] ....
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Sep 17, 2006
What is the difference please?
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Jul 31, 2000
I need a script to drop all statistics in a database at once.
HELP!
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Jun 14, 2001
I want to be able to generate a script that gives me all statistics that are in my database currently.
Does anyone know how to do this? Is the following correct:
select --a.id as SysIndex_id,
'create statistics ' + a.name + ' on ' + b.name + ' (' + SUBSTRING(A.NAME, 9, LEN(A.NAME)-17) + ')'
as SysIndex_name
--b.name
from
sysindexes A left join sysobjects B
on A.id = B.id
where a.name like '%wa%'
order by b.name
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Aug 3, 2007
Hi all,
As part of my automagical nightly index maintenance application, I am seeing a fairly regular (3-4 failures out of 5 attempts per week) failure on one particular table in my database. The particular line which seems to be failing is this one:
DBCC SHOWCONTIG (WON_Staging_EPSEst) WITH FAST, TABLERESULTS, ALL_INDEXES
The log reports the following transgression(s):Msg 2767, Sev 16: Could not locate statistics 'WON_Staging_EpsEst' in the system catalogs. [SQLSTATE 42000]
Msg 0, Sev 16: [SQLSTATE 01000]
Msg 0, Sev 16: -------------------- Simple ReIndex for [WON_Staging_EpsEst].[IX_WON_Staging_EpsEst] [SQLSTATE 01000]
Msg 2528, Sev 16: DBCC execution completed. If DBCC printed error messages, contact your system administrator. [SQLSTATE 01000]
Msg 0, Sev 16: [SQLSTATE 01000]
Msg 0, Sev 16: -------------------- Post-Maintenance Statistics Report for WON_Staging_EpsEst [SQLSTATE 01000]
Msg 0, Sev 16: Statistics for WON_Staging_EpsEst, WON_Staging_EpsEst [SQLSTATE 01000]
Msg 2528, Sev 16: DBCC execution completed. If DBCC printed error messages, contact your system administrator. [SQLSTATE 01000]
Msg 0, Sev 16: Statistics for WON_Staging_EpsEst, IX_WON_Staging_EpsEst [SQLSTATE 01000]
Msg 2768, Sev 16: Statistics for INDEX 'IX_WON_Staging_EpsEst'. [SQLSTATE 01000]
Updated Rows Rows Sampled Steps Density Average key length
-------------------- -------------------- -------------------- ------ ------------------------ ------------------------
Aug 3 2007 3:22AM 674609 674609 196 2.0958368E-4 8.0
(1 rows(s) affected)
This table is dropped and recreated each day during a data import job. After the table is recreated and repopulated with data (using a bulk import from a flat file), the index is also recreated using the following code:CREATE INDEX [IX_WON_Staging_EpsEst]
ON [dbo].[WON_Staging_EpsEst](OSID, [Year], Period)
ON [PRIMARY]Yet more often than not, that evening, when the index maintenance job runs, it fails with the aforepasted messages complaining of being unable to find table/index statistics.
Worth noting, perhaps, is that this same process is used on roughly 10 data staging tables in this database each day, and none of the other tables fail during the index maintenance job.
Also worth noting, perhaps, is that this IDENTICAL table/code is processed in exactly the same way on TWO other servers, and the failure has not occured in any of the jobs on those other two servers (these other two servers are identical mirrors of the one failing, and contain all the same data, indicies, and everything else.
Any thoughts, suggestions for where to look, or unrestrained abusive comments regarding my ancestry?
Thanks!
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Jun 13, 2008
I have a small doubt.
If we apply a statistics command on a particular table what will it update.
Normally statistics are created automatically by the server or we have to create it.
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Jul 20, 2005
Anybody know how many companies worldwide use SQL server and how manyindividual servers this amounts to? Also, at what rate is SQL usegrowing? Can someone at least point me to a source where I could findclose to exact numbers?
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Jun 20, 2001
Here my data sample on which I need to perform some stats
Time(Sec) Result
1 2
2 8
3 6
4 2
5 2
6 4
7 2
8 7
9 8
What I need from this is a result set that looks as follows
GroupNo Value
1 5.33
2 2.67
3 5.67
This is a grouping of the result data in 3's by time. Value is the average of the Group.
In need to write a select statement to do this.
Note the Group could be done from 1 to 10
The end result of this is to display a Range Chart which shows Results grouped according to requirements.
Any Help would nice.
Pargat
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Oct 10, 2001
Hello List,
I would like to know, How can I drop Statistics from tables. My user tables has two indexes and and some statistics created onto them. I would like to drop the statistics indexes and apprecaite, If someone please advice.
The statistics indexes looks something like this:
"_WA_Sys_status_01EAB64E"
Any help would be apprecaited.
Thanks,
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Jun 6, 2000
What are some ways to analyze index coverage and usage? I have a 18 GB database, half is data, other half is indexes and I want to cut down that number as much as I can without affecting performance. Thanks
Peter Karhatsu
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Nov 17, 2000
Does anyone have any generic scripts that Drop all the statistics that SQL auto generates?? I have hundreds of '_WA_....'
indicies that are auto created by SS7 and I just want to get rid of ALL of them. Thanks!
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Feb 14, 2001
I have been monitoring some indexes on a table with a lot of inserts, no updates and no deletes. I was wanting to determine when to update the statistics on the index. Does anyone know what would be a good target range for the density when you run the dbcc show_statistics?
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Jun 14, 2000
When the "create statistics" command is run, what table entries are made into system tables?
I want to check for the existence of statistics on certain columns and if they are not there, create them. What is a good way to see if they are already created?
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Feb 6, 2001
I am using SQL 6.5. We have tables of upto 2.5GB in size. Running update statistics againts these tables takes too long, and locks out users.
Anyone know how I can make this quicker?
Davy
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Jun 9, 2000
I was wondering how often you should reindex. By looking at dbcc showcontig and statistics I see that I am heavily fragmented and scan density is between 10-30% on my important indexes. I'm thinking of scheduling this to be done nightly. nay help is much appreciated.
Pete Karhatsu
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Dec 9, 2004
Hi,
I am contemplating creating a job to execute every 5 mins which will update index statisics if they are more than say 8% out. I would like to know what thoughts people have on this? i.e. pros and cons.
I like forward to what you have to say.
I have auto stats on. Our stats are often more than 10% out. At what level do you reckon the query plan might be effected by out of data stats?
Thanks
Jamie.
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Dec 7, 2005
Is the Update Statistics found in a Maintenance Plan performed online or offline? Will it kick users out when this is run on SQL Server 2000?
Thanks
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Sep 6, 2006
Hi,
It seems to me there are many ways to update statistics for a table. i.e. "sp_updatestats", "sp_recompile", "dbcc updateusage"
Can somebody tell me the difference between those commands and what's the best way for updating your statistics? Does reindexing update the statistics?
thx,
Wilfred van Dijk
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Feb 12, 2002
Can I copy statistics in SQL Server from one environment to another without copying the actual data. For example from production to development. It is possible to copy statistics in other databases, like DB2/UDB, Oracle. Reason is to execute some poor performing SQLs and analyze their execution plan.
Did not find anything on this subject in BOL. Since statistics is stored in the statblob column of sysindexes, I tried updating statblob column of the index and rowcnt columns of table & index to mimic the copy. After my updates to 'TO' table
dbcc show_statistics ( stat_test2, stat_test2_idx)
showed the results that is identical to the statistics of my FROM table.
But when I execute a small SELECT on (FROM) table(which contains the original, required stats) and the (TO) table (where the statistics is now copied), I get 2 different execution plans. This means I am not successful in my attempt to cheat the optimizer.
Is there any more columns to be updated?
Is there another direct way to do this?
Thanks in advance.
Gana.
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Nov 5, 1999
I am supporting a SQL Server 6.5 databases that users query using
pre-configured reports. The reports use views, stored procedures,
and triggers set up by the programmers and accessed thru a client
on the workstation.
I need to be able to count which users log in (SQL Server security),
how often, and either which reports they use or what tables they
select.
I do not have access to the WindowsNT server, so the solution
has to work with SQL Server SA rights.
Thanks for any suggestions.
Joan
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Aug 6, 2004
Hi,
another daily problem ...
I've a table with half million records that my application uses continious with several UPDATE e SELECT statement (about 5 requests/sec).
After several (4-5) hours I've a degrade of performance, but if I update the statistics (of thi table) all return ok.
Now the situation is I create a job to maintenance this table updating statististic two times a day ....
Is it normal? SQL should update statistics by itself?
I choose the wrong way or ... what can i do?
Thx
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Jan 17, 2007
Hi All,
I have few quries
1) Do we need downtime or to make database offline while updating statistics for table? Or this can be done online?
2) If this can be done online, will it consume CPU or memory?
3) Will the log file will grow during statistics updation?
Thanks in Advance
Regards
SS
Don't sit back because of failure. It will come back to check if you still available. -- Binu
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