Thursday, March 29, 2012

Estimating the Size of a Clustered Index

Dear All,
I am trying to calculate the size of a cluster index using the "Estimating
the Size of a Clustered Index" section of Books online. Can some body tell me
what the below formula means
Calculate the number of pages in the index:
Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
where 1 <= Level <= LevelsShri.DBA wrote:
> Dear All,
> I am trying to calculate the size of a cluster index using the "Estimating
> the Size of a Clustered Index" section of Books online. Can some body tell me
> what the below formula means
> Calculate the number of pages in the index:
> Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
> where 1 <= Level <= Levels
>
for each value of variable 'level' between 1 and Levels (levels is
variable calculated earlier):
calculate (Index_Rows_Per_Page)^(Level â' 1)
sum all (Index_Rows_Per_Page)^(Level â' 1)
I used ^ to mark exponent
that means:
let's say we have 3 levels, Levels=3:
calculate:
- for level = 1: (Index_Rows_Per_Page)^(1 â' 1) =(Index_Rows_Per_Page)^0=1
- for level = 2: (Index_Rows_Per_Page)^(2 â' 1) =(Index_Rows_Per_Page)^1=Index_Rows_Per_Page
- for level = 3: (Index_Rows_Per_Page)^(3 â' 1) =(Index_Rows_Per_Page)^2=Index_Rows_Per_Page*Index_Rows_Per_Page
now, sum all these: 1 + Index_Rows_Per_Page +
Index_Rows_Per_Page*Index_Rows_Per_Page
OK?|||> Can some body tell me
> what the below formula means
The calculation means that the number of non-leaf node index pages required
for a clustered index is the sum of the number pages need at all levels.
The number of required pages at a given level is Index_Rows_Per_Page to the
power of level - 1. Below is the Transact-SQL equivalent.
DECLARE
@.Num_Index_Pages int,
@.Index_Rows_Per_Page int,
@.Level int
SELECT
@.Num_Index_Pages = 0,
@.Index_Rows_Per_Page = 10,
@.Level = 3 --init at number of levels
WHILE @.Level > 0
BEGIN
SET @.Level = @.Level - 1
SET @.Num_Index_Pages = @.Num_Index_Pages + POWER(@.Index_Rows_Per_Page,
@.Level)
END
SELECT @.Num_Index_Pages AS Num_Index_Pages
--
Hope this helps.
Dan Guzman
SQL Server MVP
"Shri.DBA" <ShriDBA@.discussions.microsoft.com> wrote in message
news:5634D0D1-7B1F-4D3A-8878-DE30960D7255@.microsoft.com...
> Dear All,
> I am trying to calculate the size of a cluster index using the "Estimating
> the Size of a Clustered Index" section of Books online. Can some body tell
> me
> what the below formula means
> Calculate the number of pages in the index:
> Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
> where 1 <= Level <= Levels
>|||"Zarko Jovanovic" wrote:
> Shri.DBA wrote:
> > Dear All,
> >
> > I am trying to calculate the size of a cluster index using the "Estimating
> > the Size of a Clustered Index" section of Books online. Can some body tell me
> > what the below formula means
> >
> > Calculate the number of pages in the index:
> >
> > Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
> >
> > where 1 <= Level <= Levels
> >
> >
> for each value of variable 'level' between 1 and Levels (levels is
> variable calculated earlier):
> calculate (Index_Rows_Per_Page)^(Level â' 1)
> sum all (Index_Rows_Per_Page)^(Level â' 1)
> I used ^ to mark exponent
> that means:
> let's say we have 3 levels, Levels=3:
> calculate:
> - for level = 1: (Index_Rows_Per_Page)^(1 â' 1) => (Index_Rows_Per_Page)^0=1
> - for level = 2: (Index_Rows_Per_Page)^(2 â' 1) => (Index_Rows_Per_Page)^1=Index_Rows_Per_Page
> - for level = 3: (Index_Rows_Per_Page)^(3 â' 1) => (Index_Rows_Per_Page)^2=Index_Rows_Per_Page*Index_Rows_Per_Page
> now, sum all these: 1 + Index_Rows_Per_Page +
> Index_Rows_Per_Page*Index_Rows_Per_Page
> OK?
>
----
Some how I am not conveniced with this formula for calculating the number of
index pages.
I have created below table and loaded 1000000 records. When I calculate the
number of index pages it gives me 387507 pages. I don't understand why so
many index pages are required to store clustered index key size of 4 bytes.
Regards
Balaji
USE [MyDB]
GO
/****** Object: Table [dbo].[Log] Script Date: 10/30/2007 17:39:04 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[Log](
[LogID] [int] IDENTITY(1,1) NOT NULL,
[LogMessage] [varchar](50) NOT NULL,
[LogDateTime] [datetime] NOT NULL,
CONSTRAINT [PK_Log] PRIMARY KEY CLUSTERED
(
[LogID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY =OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_PADDING OFF|||Balaji wrote:
> "Zarko Jovanovic" wrote:
>> Shri.DBA wrote:
>> Dear All,
>> I am trying to calculate the size of a cluster index using the "Estimating
>> the Size of a Clustered Index" section of Books online. Can some body tell me
>> what the below formula means
>> Calculate the number of pages in the index:
>> Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
>> where 1 <= Level <= Levels
>>
>> for each value of variable 'level' between 1 and Levels (levels is
>> variable calculated earlier):
>> calculate (Index_Rows_Per_Page)^(Level â' 1)
>> sum all (Index_Rows_Per_Page)^(Level â' 1)
>> I used ^ to mark exponent
>> that means:
>> let's say we have 3 levels, Levels=3:
>> calculate:
>> - for level = 1: (Index_Rows_Per_Page)^(1 â' 1) =>> (Index_Rows_Per_Page)^0=1
>> - for level = 2: (Index_Rows_Per_Page)^(2 â' 1) =>> (Index_Rows_Per_Page)^1=Index_Rows_Per_Page
>> - for level = 3: (Index_Rows_Per_Page)^(3 â' 1) =>> (Index_Rows_Per_Page)^2=Index_Rows_Per_Page*Index_Rows_Per_Page
>> now, sum all these: 1 + Index_Rows_Per_Page +
>> Index_Rows_Per_Page*Index_Rows_Per_Page
>> OK?
> ----
> Some how I am not conveniced with this formula for calculating the number of
> index pages.
> I have created below table and loaded 1000000 records. When I calculate the
> number of index pages it gives me 387507 pages. I don't understand why so
> many index pages are required to store clustered index key size of 4 bytes.
> Regards
> Balaji
> USE [MyDB]
> GO
> /****** Object: Table [dbo].[Log] Script Date: 10/30/2007 17:39:04 ******/
> SET ANSI_NULLS ON
> GO
> SET QUOTED_IDENTIFIER ON
> GO
> SET ANSI_PADDING ON
> GO
> CREATE TABLE [dbo].[Log](
> [LogID] [int] IDENTITY(1,1) NOT NULL,
> [LogMessage] [varchar](50) NOT NULL,
> [LogDateTime] [datetime] NOT NULL,
> CONSTRAINT [PK_Log] PRIMARY KEY CLUSTERED
> (
> [LogID] ASC
> )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY => OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
> ) ON [PRIMARY]
> GO
> SET ANSI_PADDING OFF
did you read whole article in BOL?|||Hi Dan Guzman,
Thanks very much for your help. I see there is a difference of 10-15% from
the calculated value and original value. Any thoughts.
Regards
Balaji
"Dan Guzman" wrote:
> > Can some body tell me
> > what the below formula means
> The calculation means that the number of non-leaf node index pages required
> for a clustered index is the sum of the number pages need at all levels.
> The number of required pages at a given level is Index_Rows_Per_Page to the
> power of level - 1. Below is the Transact-SQL equivalent.
>
> DECLARE
> @.Num_Index_Pages int,
> @.Index_Rows_Per_Page int,
> @.Level int
> SELECT
> @.Num_Index_Pages = 0,
> @.Index_Rows_Per_Page = 10,
> @.Level = 3 --init at number of levels
> WHILE @.Level > 0
> BEGIN
> SET @.Level = @.Level - 1
> SET @.Num_Index_Pages = @.Num_Index_Pages + POWER(@.Index_Rows_Per_Page,
> @.Level)
> END
> SELECT @.Num_Index_Pages AS Num_Index_Pages
> --
> Hope this helps.
> Dan Guzman
> SQL Server MVP
> "Shri.DBA" <ShriDBA@.discussions.microsoft.com> wrote in message
> news:5634D0D1-7B1F-4D3A-8878-DE30960D7255@.microsoft.com...
> > Dear All,
> >
> > I am trying to calculate the size of a cluster index using the "Estimating
> > the Size of a Clustered Index" section of Books online. Can some body tell
> > me
> > what the below formula means
> >
> > Calculate the number of pages in the index:
> >
> > Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
> >
> > where 1 <= Level <= Levels
> >
> >
>|||> Thanks very much for your help. I see there is a difference of 10-15% from
> the calculated value and original value. Any thoughts.
What original value are you referring to?
--
Hope this helps.
Dan Guzman
SQL Server MVP
"Balaji" <Balaji@.discussions.microsoft.com> wrote in message
news:AA2312C8-5C72-43F3-A283-E4D7AE2EFE3A@.microsoft.com...
> Hi Dan Guzman,
> Thanks very much for your help. I see there is a difference of 10-15% from
> the calculated value and original value. Any thoughts.
> Regards
> Balaji
> "Dan Guzman" wrote:
>> > Can some body tell me
>> > what the below formula means
>> The calculation means that the number of non-leaf node index pages
>> required
>> for a clustered index is the sum of the number pages need at all levels.
>> The number of required pages at a given level is Index_Rows_Per_Page to
>> the
>> power of level - 1. Below is the Transact-SQL equivalent.
>>
>> DECLARE
>> @.Num_Index_Pages int,
>> @.Index_Rows_Per_Page int,
>> @.Level int
>> SELECT
>> @.Num_Index_Pages = 0,
>> @.Index_Rows_Per_Page = 10,
>> @.Level = 3 --init at number of levels
>> WHILE @.Level > 0
>> BEGIN
>> SET @.Level = @.Level - 1
>> SET @.Num_Index_Pages = @.Num_Index_Pages + POWER(@.Index_Rows_Per_Page,
>> @.Level)
>> END
>> SELECT @.Num_Index_Pages AS Num_Index_Pages
>> --
>> Hope this helps.
>> Dan Guzman
>> SQL Server MVP
>> "Shri.DBA" <ShriDBA@.discussions.microsoft.com> wrote in message
>> news:5634D0D1-7B1F-4D3A-8878-DE30960D7255@.microsoft.com...
>> > Dear All,
>> >
>> > I am trying to calculate the size of a cluster index using the
>> > "Estimating
>> > the Size of a Clustered Index" section of Books online. Can some body
>> > tell
>> > me
>> > what the below formula means
>> >
>> > Calculate the number of pages in the index:
>> >
>> > Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
>> >
>> > where 1 <= Level <= Levels
>> >
>> >|||Hi Dan,
The original value I am referring to here is the result of sp_spaceused.
Regards
Balaji.T
"Dan Guzman" wrote:
> > Thanks very much for your help. I see there is a difference of 10-15% from
> > the calculated value and original value. Any thoughts.
> What original value are you referring to?
> --
> Hope this helps.
> Dan Guzman
> SQL Server MVP
> "Balaji" <Balaji@.discussions.microsoft.com> wrote in message
> news:AA2312C8-5C72-43F3-A283-E4D7AE2EFE3A@.microsoft.com...
> > Hi Dan Guzman,
> >
> > Thanks very much for your help. I see there is a difference of 10-15% from
> > the calculated value and original value. Any thoughts.
> >
> > Regards
> > Balaji
> >
> > "Dan Guzman" wrote:
> >
> >> > Can some body tell me
> >> > what the below formula means
> >>
> >> The calculation means that the number of non-leaf node index pages
> >> required
> >> for a clustered index is the sum of the number pages need at all levels.
> >> The number of required pages at a given level is Index_Rows_Per_Page to
> >> the
> >> power of level - 1. Below is the Transact-SQL equivalent.
> >>
> >>
> >> DECLARE
> >> @.Num_Index_Pages int,
> >> @.Index_Rows_Per_Page int,
> >> @.Level int
> >> SELECT
> >> @.Num_Index_Pages = 0,
> >> @.Index_Rows_Per_Page = 10,
> >> @.Level = 3 --init at number of levels
> >> WHILE @.Level > 0
> >> BEGIN
> >> SET @.Level = @.Level - 1
> >> SET @.Num_Index_Pages = @.Num_Index_Pages + POWER(@.Index_Rows_Per_Page,
> >> @.Level)
> >> END
> >> SELECT @.Num_Index_Pages AS Num_Index_Pages
> >>
> >> --
> >> Hope this helps.
> >>
> >> Dan Guzman
> >> SQL Server MVP
> >>
> >> "Shri.DBA" <ShriDBA@.discussions.microsoft.com> wrote in message
> >> news:5634D0D1-7B1F-4D3A-8878-DE30960D7255@.microsoft.com...
> >> > Dear All,
> >> >
> >> > I am trying to calculate the size of a cluster index using the
> >> > "Estimating
> >> > the Size of a Clustered Index" section of Books online. Can some body
> >> > tell
> >> > me
> >> > what the below formula means
> >> >
> >> > Calculate the number of pages in the index:
> >> >
> >> > Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
> >> >
> >> > where 1 <= Level <= Levels
> >> >
> >> >
> >>
>|||> The original value I am referring to here is the result of sp_spaceused.
Perhaps extra space is required due to fragmentation.
--
Hope this helps.
Dan Guzman
SQL Server MVP
"Balaji" <Balaji@.discussions.microsoft.com> wrote in message
news:CE6A90B3-E3D1-4CD1-A67F-B6DA9F78D754@.microsoft.com...
> Hi Dan,
> The original value I am referring to here is the result of sp_spaceused.
> Regards
> Balaji.T
> "Dan Guzman" wrote:
>> > Thanks very much for your help. I see there is a difference of 10-15%
>> > from
>> > the calculated value and original value. Any thoughts.
>> What original value are you referring to?
>> --
>> Hope this helps.
>> Dan Guzman
>> SQL Server MVP
>> "Balaji" <Balaji@.discussions.microsoft.com> wrote in message
>> news:AA2312C8-5C72-43F3-A283-E4D7AE2EFE3A@.microsoft.com...
>> > Hi Dan Guzman,
>> >
>> > Thanks very much for your help. I see there is a difference of 10-15%
>> > from
>> > the calculated value and original value. Any thoughts.
>> >
>> > Regards
>> > Balaji
>> >
>> > "Dan Guzman" wrote:
>> >
>> >> > Can some body tell me
>> >> > what the below formula means
>> >>
>> >> The calculation means that the number of non-leaf node index pages
>> >> required
>> >> for a clustered index is the sum of the number pages need at all
>> >> levels.
>> >> The number of required pages at a given level is Index_Rows_Per_Page
>> >> to
>> >> the
>> >> power of level - 1. Below is the Transact-SQL equivalent.
>> >>
>> >>
>> >> DECLARE
>> >> @.Num_Index_Pages int,
>> >> @.Index_Rows_Per_Page int,
>> >> @.Level int
>> >> SELECT
>> >> @.Num_Index_Pages = 0,
>> >> @.Index_Rows_Per_Page = 10,
>> >> @.Level = 3 --init at number of levels
>> >> WHILE @.Level > 0
>> >> BEGIN
>> >> SET @.Level = @.Level - 1
>> >> SET @.Num_Index_Pages = @.Num_Index_Pages +
>> >> POWER(@.Index_Rows_Per_Page,
>> >> @.Level)
>> >> END
>> >> SELECT @.Num_Index_Pages AS Num_Index_Pages
>> >>
>> >> --
>> >> Hope this helps.
>> >>
>> >> Dan Guzman
>> >> SQL Server MVP
>> >>
>> >> "Shri.DBA" <ShriDBA@.discussions.microsoft.com> wrote in message
>> >> news:5634D0D1-7B1F-4D3A-8878-DE30960D7255@.microsoft.com...
>> >> > Dear All,
>> >> >
>> >> > I am trying to calculate the size of a cluster index using the
>> >> > "Estimating
>> >> > the Size of a Clustered Index" section of Books online. Can some
>> >> > body
>> >> > tell
>> >> > me
>> >> > what the below formula means
>> >> >
>> >> > Calculate the number of pages in the index:
>> >> >
>> >> > Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
>> >> >
>> >> > where 1 <= Level <= Levels
>> >> >
>> >> >
>> >>|||Ok...thank you very much for the reply.
"Dan Guzman" wrote:
> > The original value I am referring to here is the result of sp_spaceused.
> Perhaps extra space is required due to fragmentation.
> --
> Hope this helps.
> Dan Guzman
> SQL Server MVP
> "Balaji" <Balaji@.discussions.microsoft.com> wrote in message
> news:CE6A90B3-E3D1-4CD1-A67F-B6DA9F78D754@.microsoft.com...
> > Hi Dan,
> >
> > The original value I am referring to here is the result of sp_spaceused.
> >
> > Regards
> > Balaji.T
> >
> > "Dan Guzman" wrote:
> >
> >> > Thanks very much for your help. I see there is a difference of 10-15%
> >> > from
> >> > the calculated value and original value. Any thoughts.
> >>
> >> What original value are you referring to?
> >>
> >> --
> >> Hope this helps.
> >>
> >> Dan Guzman
> >> SQL Server MVP
> >>
> >> "Balaji" <Balaji@.discussions.microsoft.com> wrote in message
> >> news:AA2312C8-5C72-43F3-A283-E4D7AE2EFE3A@.microsoft.com...
> >> > Hi Dan Guzman,
> >> >
> >> > Thanks very much for your help. I see there is a difference of 10-15%
> >> > from
> >> > the calculated value and original value. Any thoughts.
> >> >
> >> > Regards
> >> > Balaji
> >> >
> >> > "Dan Guzman" wrote:
> >> >
> >> >> > Can some body tell me
> >> >> > what the below formula means
> >> >>
> >> >> The calculation means that the number of non-leaf node index pages
> >> >> required
> >> >> for a clustered index is the sum of the number pages need at all
> >> >> levels.
> >> >> The number of required pages at a given level is Index_Rows_Per_Page
> >> >> to
> >> >> the
> >> >> power of level - 1. Below is the Transact-SQL equivalent.
> >> >>
> >> >>
> >> >> DECLARE
> >> >> @.Num_Index_Pages int,
> >> >> @.Index_Rows_Per_Page int,
> >> >> @.Level int
> >> >> SELECT
> >> >> @.Num_Index_Pages = 0,
> >> >> @.Index_Rows_Per_Page = 10,
> >> >> @.Level = 3 --init at number of levels
> >> >> WHILE @.Level > 0
> >> >> BEGIN
> >> >> SET @.Level = @.Level - 1
> >> >> SET @.Num_Index_Pages = @.Num_Index_Pages +
> >> >> POWER(@.Index_Rows_Per_Page,
> >> >> @.Level)
> >> >> END
> >> >> SELECT @.Num_Index_Pages AS Num_Index_Pages
> >> >>
> >> >> --
> >> >> Hope this helps.
> >> >>
> >> >> Dan Guzman
> >> >> SQL Server MVP
> >> >>
> >> >> "Shri.DBA" <ShriDBA@.discussions.microsoft.com> wrote in message
> >> >> news:5634D0D1-7B1F-4D3A-8878-DE30960D7255@.microsoft.com...
> >> >> > Dear All,
> >> >> >
> >> >> > I am trying to calculate the size of a cluster index using the
> >> >> > "Estimating
> >> >> > the Size of a Clustered Index" section of Books online. Can some
> >> >> > body
> >> >> > tell
> >> >> > me
> >> >> > what the below formula means
> >> >> >
> >> >> > Calculate the number of pages in the index:
> >> >> >
> >> >> > Num_Index_Pages = â'Level (Index_Rows_Per_Page)Level â' 1
> >> >> >
> >> >> > where 1 <= Level <= Levels
> >> >> >
> >> >> >
> >> >>
> >>
>

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