Hi,
I am studying for MCTS and through some of the course material it recommends that a low selectivity field i.e. First Name is a good canditate for a clustered index.
This goes against what is recommended online (completely the opposite) and goes against what I have been taught in the past.
What is correct for the exam?
Thanks
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?
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] ....
What is the easiest way to remember the definitions of clustered and non clustered indexes.
View 9 Replies View RelatedI would like to find information on Clustered and Non-clustered indexes and how B-trees are used. I know a clustered index is placed into a b-tree which makes sense for fast ordered searching. What data structure does a non-clustered index use and how? I tried to find info. on the web but couldn't get much detail...
View 3 Replies View RelatedHi,I am expanding our data warehouse solution with new filegroups onseveral subsystems.I want to know which idea is better!- create clustered indexes on tables to 'move' them to new filegroups- create these tables on the new filegroups.The background of this question is as follows:- we want the whole data on the new filegroups- we want to know if there is any difference in performance between the2 solutionsThanks in advance,Danny
View 4 Replies View Relatedhi,
how clustered indexes and non-clustered indexes been saved in memory?
non-clustered is a table of a references to the actual table?
and what about clustered indexes?
thanks.
Can anyone help ?
If you have a clustered index on an identity field are appends then forced onto the last page anyway because of the identity field order. So is there any advanbtage of having a clustered identity field ?
I need to convert several tables that currently have nonclustered indexes (primary keys) to clustered. Could anyone suggest what the easiest way of doing this would be.
View 1 Replies View Relatedhi
can someone tell me why there are only 249 non-clustered indexes,
is there any significance to that number
Hi,The more I read, the more confused I'm getting ! (no wonder they sayignorance is bliss)I just got back from the bookstore and was flipping through some SQL ServerAdministration books.One says, that to get the best query performance, youi do two things:1. Cover all the columns used in each SELECT (including the WHERE, ORDERBY , etc.) with an index2. Make sure it's a NON-CLUSTERED index.In this way, the author says, you avoid ever going directly to the basetables for data to resolve the query - i.e. it's resolved in the index.So, for example, he argues if you have:SELECT Lname,Fname, CompanyNamefrom Contactsinner join Customerson (contacts.custid = customers.custid)that you use two non-clustered indexes:1. Lname,Fname and custid from the Contacts table2. CompanyName and custid from Customers(as opposed to the standard approach of a clustered index on the PK's ofeach table)He says that clustered indexes don't speed up performance because they'rethe same as a full table scan. Should I drop clustered indexes from mylarge tables, given that there are multiple non-clustered indexes on them?Is it better to just use multiple non-clustered indexes on a heap table?Steve
View 1 Replies View RelatedWhat is the difference please?
View 1 Replies View RelatedSQL 7 created by default a clustered index on my primary key field. I would like to drop this index and recreate it on another field, but it is not allowing me. Error message states: "An explicit DROP INDEX is not allowed... It is being used for PRIMARY KEY CONSTRAINT enforcement." Can anybody advise how I can solve this? TIA
View 1 Replies View RelatedIs any one know of a way of changing the clustered index without creating in the middle the default clustered index
we have a big table that we use to switch the clustered index
whenever we change the clustered index we cannot change it directly we have
to drop the existing than the default clustered is built
and than we can built the new one - since it is a big table the process
takes a lot of time and I wonder if we can do it directly from one cluster
index to another
What we do not is running the following SQL:
-- remove the old index
drop index Tbl.I_oldId
GO
-- now create the newId as clustered
CREATE CLUSTERED
INDEX [I_newId] ON Tbl ([newId])
ON [PRIMARY]
GO
Any Idea ?
Thanks
David
Using SQL Server 2000 ... hopefully not too dumb a question.
Is there a performance hit using Clustered Index on a table that gets a lot of deletes?
I'm creating a Transaction Log table that will get about 4,000 inserts per day. The value of some of this historical data is worthless after a while, so I delete it.
It occurs to me that this may create a lot of fragmentation. If so, is this cleaned up during weekly "Reorganize data and index pages" in the Maintenance Plan? Do I also need to select "Remove unused space from database files"?
Additional question: I though that care needed to be taken that a clustered key be a value that always increments (datestamp, identity key, etc), yet in this write-up, it shows using randomly generated key values. I'm confused. Wouldn't it have to reorganize everything with greater values to insert the new row into the appropriate spot?
http://www.sql-server-performance.com/gv_clustered_indexes.asp
Greetings all,
What's best practice for creating clustered indexes?! Should they be added to a table AFTER it has been populated or should the clustered index be created BEFORE?
Thanks for your advice in advance.
When you Upsize from Access using the wizard, unsurprisingly, a Unique index is created on the PK field, but these are all non-clustered. I presume there isn't one definitive answer to whether a index should be clustered or not, (which I understand means the table's records are held on disk contiguously), but generally, is it worth altering these all to become clustered?
Would you selectively cluster only those tables which you think would benefit most? Leave them all unclustered and look for bottle-necks?
1) is there a way in ss2005 to filter out nulls from a non clustered index?
2) if nulls are allowed in a non clustered non unique index, is there anything worth knowing about performance? I assume such an index would assist in a query that asks for rows where col A is or isnt null, but might it be better for us to reserve some invalid values for cols that would otherwise have been null and been in such an index? I'm worried specifically about a very large table we'll have, indexed on 2 columns that 50% of the time are both null. Partitioning isnt an option.
Does anyone have a recommendation for creating an index on a datetime column?
We use alot of dateranges in our statements and none of them perform very well.
Thanks
Pete Karhatsu
OK so I have this EAV system on a server that is old enough for kindergarten. Insanely enough, this company that makes more money than any of your gods can not buy me a new box.
Before you say "redesign", I need funding allocated for that. See my first statement.
Anywho, I have this page that touches the dreaded Value table and does a clustered index seek on it. Can't search faster than that, right? Well I am getting some funding for "performance tuning". I am wondering if maybe incorporating some clustered index views involving the value table and producing a smaller clustered index for it to seek may alleviate some of this. Any thoughts?
Currently we are facing some performance issue while accessing the archive data from the archive tables. the archive table is hugh and it contains around 100,000,000 records and this archive table is being used in few reports and in our commission cycles too. since we are facing performance issues we are rebuilding index once in a week on all the indexes on this archive table.
We have 1 clustered index and 5 non clustered indexes, every time when we rebuild all these indexes on this table it is taking more time, more often rebuilding the clustered index itself is taking approx. 1hr which is consuming more time. wanted to know is there any useful to rebuild clustered indexes or not, if yes then what would be the better way. if not then do we need to rebuild only non clustered indexes.
All of the 3 books I've read say it is not a good idea to create a clustered index on the primary key but it is created as the default. My question is has this changed in 2005? My understanding is to create the clustered index on columns used first in join clauses and then in where clauses, what is the answer?
View 14 Replies View RelatedI set up replication on our servers at work to streamline some procedures we run daily/weekly on them. This copies around 15 articles from two databases on the "Master" server to another server used for execution purposes. For the most part it was a pretty straight forward task and it seemed to work nicely; but I realised after some investigation that the non-clustered indexes weren't copying over to the child server.
I set the non-clustered indexes property in the properties of the publishing articles to "True" and generated a new snapshot, this seemed to work, but I've come into work this morning to find the property has reset to "False" and I have no indexes on the table again. Why is this happening and is there any way I can resolve the matter so the indexes are copied over concurrently?
Group,
I am getting the following error during replication of Database to a client:
The schema script 'Statutes_6.dri' could not be propagated to the subscriber. (Source: MSSQL_REPL, Error number: MSSQL_REPL-2147201001)
Get help: http://help/MSSQL_REPL-2147201001
Invalid locale ID was specified. Please verify that the locale ID is correct and corresponding language resource has been installed. (Source: MSSQLServer, Error number: 7696)
Get help: http://help/7696
Incorrect syntax near the keyword 'with'. If this statement is a common table expression or an xmlnamespaces clause, the previous statement must be terminated with a semicolon. (Source: MSSQLServer, Error number: 319)
The database is relatively small, only about 5 tables but there is a clustered Full-text Index.
Any ideas?
Thanks,
Frank
I have a database where records are Inserted by an external process.
There is no updating or deleting of the data once inserted. The table in
question has a Clustered Index on the Machine_ID (integer) (data is from
manufacturing processes). Each record bears a start and end time. Most
queries involve the Machine, a time span (start time between to points in
time), the Downtime Cause, and the Running Mode.
I want to add an index on the Start Time, the Downtime Cause, and the
Runtime Mode.
My question is: should this new index also contain the Machine_id column
or does the existence of the Clustered Index already on that column negate
its need in the new index?
RC - Dedicated to only creating original mistakes!
I've been asked to look at using Clustered Columnstore indexes for one of my tables. The table contains about 5 million records with about 50 columns. The max field size is a NVarchar(MAX) with max field length currently of about 4k characters. It's only about a gigabyte's worth of data. The table is about 50% R/W operations. Currently, we have multiple indexes with no clustered index due to some performance issues that happened in the past. I've been attempting to determine if it's even really worth it to switch over. I feel that the table is still fairly small with minimal columns and don't believe there will be any noticeable improvement over traditional indexing.
View 3 Replies View RelatedI have a database in which I have some tables in which I have implemented Clustered columnstore Index. How to find the fragmentation levels of all these indexes via a single T-SQl script
View 3 Replies View RelatedWhy should we consider selectivity of a table to create index?
Which is best selectivity value to create an index ?
Hi,
Is there a way to configure mirroring to go from High Availability to High Protection without having to reconfigure Database Mirroring? Using the interface in Management Studio, I can change the configuration option to High Performance, but not High Protection despite both of them being Synchronous.
If not, what are the recommended steps to configure the mirror once it already has been configured? Is just like initially setting up the mirror or would there be any shortcuts I could take? If I stop the mirroring and remove the witness, will the High Protection option be available?
Thanks,
J.
Hi There
I realise this is a stupid quesiton but i cannot really find any confirmation of this in BOL.
If you are running High Safety with automatic failover, when failover occurs does this automatically change to High Performance mode. SInce for failover to occur something has happen with the primary , it will be impossible to commit transactions on the new primary and mirror asyncronously since 1 of them is no longer available.
So am i correct in assuming that automatic failover also automatically changes the mode to High Performacne for that session?
Thanx
We are going to use SQL Sever change tracking. The problem is that some of our tables, which are to be tracked, have no primary keys. There are only unique clustered indexes. The question is what is the best way to turn on change tracking for these tables in our circumstances.
View 4 Replies View RelatedI desire to have a clustered index on a column other than the Primary Key. I have a few junction tables that I may want to alter, create table, or ...
I have practiced with an example table that is not really a junction table. It is just a table I decided to use for practice. When I execute the script, it seems to do everything I expect. For instance, there are not any constraints but there are indexes. The PK is the correct column.
CREATE TABLE [dbo].[tblNotificationMgr](
[NotificationMgrKey] [int] IDENTITY(1,1) NOT NULL,
[ContactKey] [int] NOT NULL,
[EventTypeEnum] [tinyint] NOT NULL,
[code]....
I have created two tables. table one has the following fields,
Id -> unique clustered index.
table two has the following fields,
Tid -> unique clustered index
Id -> foreign key of table one(id).
Now I have created primary key for the table one column 'id'. It's created as "nonclustered, unique, primary key located on PRIMARY". Primary key create clustered index default. since unique clustered index existed in table one, it has created "Nonclustered primary key".
My Question is, What is the difference between "clustered, unique, primary key" and "nonclustered, unique, primary key"? Is there any performance impact between these?