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
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
View 5 Replies View RelatedHi all,
I'm using SQL 7, there is a setting on DB properties called "Auto update statistics", what kind of statistics does this refers to and how can this stats be accessed?
Thanks for your help!
Gustavo
Thanks,
GS
I have Auto Create Statistics and Auto Update Statistics ON in one of my databases.
How do I know what time the Auto Update Statistics Kicks on ?
I dont see it in the log.
Is there a way for me to find out when was the last time Auto Update Statistics kicked on?
TIA
Hi all,
We are using SQL Server 2005. The auto update statistics and auto create statistics for a database is set to ON. This database has a very heavy work load. When I checked the individual statitics , still the last updated statistics is in a old date value (few months ago).
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,
Hariarul
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
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?
I have a series of indexes that are showing as statistics. Is it because they are filtered or are defined as constraints?
View 5 Replies View RelatedMy question: Is it okay to drop all the auto generated column statistics? (for the following scenario)
- I am cleaning up unnecessary objects (tables, unused indexes, overlapping statistics etc) from databases and found out there are more than 1400 auto generated column statistics on one database (lets call it A).
- 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.
We have implemented a very small reporting database which has a main table that started off small and has now grown to around half a million rows. Initially, there were no indexes on the table apart from a clustered index, but as the data has grown, performance has dropped and so we have added a number of indexes. This has resolved the performance issues.
Before creating the indexes SQL Server had auto created a number of statistic objects (_WA_Sys_000... etc). After creating the indexes, new statistic objects where created for the new indexes. In some cases, there are duplicate statistics (auto and index) for the same columns.Should I go through and drop the duplicate auto statistics? Will having duplicates cause issues at all?
Over the past week and a half we started experiencing a sporadic slowdown in our production x64 SQL 2005 Ent. Edition server. Users started complaining of slowness then they started getting timeouts. In looking at sp_who2 and perfmon we saw the following during the slow/frozen periods:
* Dramatic increase in Perfmon Active Transactions
* CPU higher than norm, but not dramatically so
* sp_who2 shows a number of spids in SUSPENDED state (and not running waits)
* no blocking indicated from sp_who2
* active connections slowly increasing
* no disk queuing (or at most some spikes to 1)
After a couple of minutes of this we would then see the following:
* no more spids in SUSPENDED state
* Logins per second spikes dramatically
* Active transactions spikes down to "normal levels"
* CPU goes high then levels out at moderately higher than normal
* active connections slowly decreases back towards normal levels
* large spike in lock wait time
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?
Anyone?
Thx
Ron
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?
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?
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?
Does the create statistics on an index on a table leave the table usable? Meaning is it an online operation? Also, I don't really get how it improves performance after reading the BOL.
-Kyle
statistics in sql server. how to create it and update it on tables.?
View 9 Replies View RelatedHow does one figure out, I mean compare the results after some changes have been done to the SQL Server, I mean the method in which the comparision is done, lets say I have a query I ran it it gave me the results in 40 seconds , I ran it again this time it took 30 seconds, then I again ran it it took 35 seconds, I then created an index , this time the query ran in 30 seconds ... how does one compare such things , I mean i need to give stats as too what kind of performace has takern place ... please helpo , I need to knw as a DBa how would you convince your maanger that becasue of some changes the performance has improved, cause when you ask the users they say its ok , we dont see the differnece & stuff , please help.
View 1 Replies View RelatedI created a table with a field called myID. I set the data type as "uniqueidentifier", but it won't auto generate. How do I create a field to auto generate a unique number? I'm working with SQL Server 2000 and I'm creating the table from Enterprise Manager.
View 5 Replies View RelatedWhen creating the indexes on the table, SQL 7.0 also created some type of system indexes ( ex. _WA_Sys_curr_int_rate_2C88998B nonclustered, statistics, auto create located on PRIMARY, etc. ). I want to know how can I clear up these system indexes.
View 1 Replies View RelatedSlayer writes "Probably a really lame question but in the absence of our DBA I have been asked to create a couple of indexes on a table. No problem with that, just need to know if this is a safe operation whilst users are using the database.
Thanks for your help"
Hi all
I just got SQL server 2k5 installed and working....im just trying to figure out how to make an auto incremement column wiht an integer..
or has it been replaced with the "unique identifyer"
Abyss
how can i create an auto number field in sql server 2000?
thanks kris
Hello,
A few months ago, the company I work for switched to SQL 7.0 from 6.5. All is running fine but recently I noticed that we have a ton of indexes on each table that start like this: _WA_SYS_....0B679CE2 (here are some specific examples: _WA_SYS_PRODUCT_LINE_0B679CE2, _WA_SYS_RMA_DISPOSITION_0B679CE2)
Did SQL 7.0 do this? If so why? What is it trying to do? Why doesn't it use current indexes (clustered and non-clustered)? Why don't they get Fragmented like User defined indexes? I have a lot of questions associated with this if someone can explain it.
Tech Net, MSDN, BOL and other manual resources don't mention anything about it. At least I haven't found anything on it and I have spent some time looking.
Please help if you can.
Troy
1)When we create Indexes, key columns are the columns that use in where clause and included columns are the columns that can be used in the select list and on join clause column.
2) I am thinking that we have to create new Index, only if we found at least 50 msec time save.
I found out how to create clustered index using TSQL, but how can you create clustered index and manage indexes using SQL Server Management Studio?
Thanks
Goldmember
Hi,I have a new job. It needs to drop and re-create (by insert) a tableevery night. The table contains approximately 3,000,000 (and growing)records. The insert is fine, runs in 2 minutes. The problem is thatwhen I create the indexes on the table, it is taking 15-20 minutes.There is one clustered index and 11 non-clustered. This is a lookuptable that takes many different paremeters, so it really needs theindexes for the user interface to run efficiently. However, thedatabase owners aren't keen on a job taking 20 minutes to run everynight.Any ideas?
View 5 Replies View RelatedFirst, I'd like some help stablishing if it's a good idea or not what I'm thinking, and second is what would be the easyist way to achive the result.
Background. We have a multicompany ERP system (200GB, 200+ tables). All data tables have a companyid, counter1id, counter2id, fields. Each table has a primary clusterd index on these fields in that order. And also has multiple other indexes that usually include companyid filed first. ( Note we have 10 companies, ids are 1..10, companies 2 and 5 are the most active, inserts, selects ). MY GUESS IS THAT THIS IS VERY BAD HAVING COMPANYID FIRST. AM I CORRECT? LEADS TO AL LOT OF FRAGMENTATION? VERY BAD TO FIND DATA ON THE INDEXES?
I want to re-create all my indexes and have them counter2id, companyid, counter2id. ( counter1id is a counter for each company, and counter2id is a global counter like identity ) GOOD OR BAD IDEA?
Since I have hundreds of indexes what is the correct procedure? I was thinking on scripting the database, then dropping all indexes, then recreate clustered indexes, then recreate other indexes. Do I have to take care of anything else foreing relationships, etc.
Hi does anyone know how to create a sql table and then import a list by just clicking on a button to call a procedure?CREATE TABLE clients(ClientID VARCHAR(5), ClientName VARCHAR(30), PRIMARY KEY (ClientID));LOAD DATA LOCAL INFILE 'C:/client.csv' INTO TABLE clientsLINES TERMINATED BY '
';
I am new to writing SQL code and I read that you can use ALTER statements to create an index for a table. How would I go about doing that? Everything that I have tried in Query Analyzer comes up with an error.
Any help is appreciated.
is there a function that i can use in a store procedure that allow me to create an Indexes/Keys Property
thanx
With help of others on this group, I've been learning and researchingabout indexes; an area I neglected.I see I can specify which filegroup I wish to create an index, whichthe default is Primary.I have more than one drive in my SQL server where I put data and logson their own logical raid groups.My databases are SIMPLE, so they dont use much, if any logs (none as Iunderstand).I was thinking of adding an additional file to my database and use itsolely for the indexes.Any thoughts?SQL Server 2005 Enterprise x64 SP28 disk SAS Raid 1+0 w/ 512mb ram w/ battery backup.Thanks,Rob
View 2 Replies View RelatedI have a pretty large database that has tables that will contain millions of rows of records. I will predominantly be using Views just to select the data. (I will not be performing any updates or inserts). I propose creating indexes on the views. My question is - if I create indexes on my views, do I have to create them on the tables as well? Is it good practice to create indexes on tables by default even if I am not going to be performing select statements directly on my tables but via my indexed views? Any advice is appreciated.
Thanks
Ran
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 0īs, 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 itīs possible to change the precision.
- Nikolaj