Auto Created Statistics And Missing Statistics

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 to
create, if I turn off auto-created statistics, are so important to the
optimizer?

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 index
exists for Country. BUT, the query plan also shows, that the optimizer is
missing a statistic on Country, which tells me, that the optimizer would
benefit 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 (and
why should it?). I could understand it, if the optimizer suggested an index
on Country - this would make sense, but if creating the missing index, query
analyzer creates the statistics with an empty index, which seems to me to be
less than usable.

I've been thinking long and hard about this, but haven't been able to reach
a conclusion :) It has some relevance to my work, because allowing the
optimizer to create missing statistics limits my options for designing
indexes (e.g. covering) for some rather wide tables, so I'm thinking why not
turn it off altogether. But I would like to know the consequences - hope
somebody has already delved into this, and knows a good explanation.

Rgds
Jesper

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Dec 7, 2007

Hi all,

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Is it necessary to manually update the statistics for the same database? Or can we rely upon "auto update statistics" itself ?

Usually in what frequency the manual UPDATE STATISTICS should be run on production system which has heavy transactions ?

Thanks & Regards,

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Dec 29, 2014

My question: Is it okay to drop all the auto generated column statistics? (for the following scenario)

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- Database A was used to be our reporting database but from last several years we are using database B for reporting. DB A has all the historical data while DB B only has valid records.
- We are updating all the column statistics with full scan nightly on database A and it is talking almost 2.5 hours to do that. Now I want to drop all the "unnecessary" statistics those were created when DB A was reporting database and they are no longer in use. There is no way to know the creation date of the column statistics that I know of. Statistics "last update date" is of no use because of our nightly job. So I was thinking of dropping all the auto generated column statistics and let the sql server create as it needs from now.

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After a couple of minutes of this we would then see the following:
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We turned on the Async Auto Update Statistics option (after testing in our staging environment) on the primary database about a week before we saw this problem. By turning it off we can visually see the problem go away by watching the above metrics. So my question is, What metrics can I use to see the "blocking" or resouce locking that is causing these problems?
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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,
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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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Hello List,

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