SQL SERVER – Tips from the SQL Joes 2 Pros Development Series – Sparse Data and Space Used by Sparse Data – Day 17 of 35

Answer simple quiz at the end of the blog post and -
Every day one winner from India will get Joes 2 Pros Volume 3.
Every day one winner from United States will get Joes 2 Pros Volume 3.

Sparse Data

Fields with fixed length data types (e.g., int, money) always consume their allotted space irrespective of how much data the field actually contains. This is true even if the field is populated with a null.

Occasionally you will encounter a column in your database which is rarely used. For example, suppose you have a field called [Violation] in a table called [Employee] but very few employees have any violations – perhaps two or three for every 1000 employees. In this case, over 99% of the Violation field values are null. This would be an example of a sparsely populated field.

To demonstrate a sparsely populated field, we will create a simple table with the design shown here. Create and populate the dbo.Bonus table by running this code in the figures below.

Please note that INSERT statements demonstrated will use row constructors, which debuted as a new feature in SQL Server 2008. However, readers who are running SQL Server 2005 must write their INSERT statements using the alternate syntax shown in the lower portion of the last Figure.

Now look at all the records in the table. Since all fields contain fixed length data types (i.e., int, char(2), money), we could have accurately calculated the per row consumption before we even added any data to the table.

Each row of the Bonus table will consume 21 bytes based on the data below.

  • Row Header – 4 bytes (true for all rows).
  • Fixed Data – 14 bytes (BonusID is an int (4 bytes) and BonusAmount’s data type is money (8 bytes).
  • Null Block (aka Null Bitmap) – 3 bytes

The nulls in the money field do not change the space consumption because fixed length data types always use the full amount of space allocated to them. At 21 bytes per row, 1000 rows of the Bonus table would require 21,000 bytes and fill up about 3 data pages (1 data page = 8060 bytes). Currently there are only three records in this table so just 1 data page of 8K has started to fill up.

Analyzing Space Used

A handy tool for checking the storage amount which an object occupies is sp_spaceused. The figure below shows the Bonus table passed into this stored procedure. We see the Bonus table contains three rows and its data has not yet exceeded its first 8 KB page.

If you added enough records the data space used would need more memory pages. Let’s run a loop to add 997 more records to the Bonus table. The first record populated will be row 4. This loop increments each subsequent BonusID value by 1, and the loop runs as long as the BonusID value is <=1000. Once the row containing BonusID 1000 has been entered into the table, the loop will end. One run the Bonus table contains 1000 records.

Since one row occupies 21 bytes, we know these 1000 rows will take up 21 KB of space and should fit within three data pages.

[21000 bytes/(8060 bytes/page) = 2.61 pages]

Since you can use half a data page SQL dedicated 3 data pages to the Bonus table. Let’s rerun the sp_spaceused sproc and confirm the number of data pages.

Using the Sparse Data Option

The sparse data option is a new SQL Server 2008 feature for fields you expect to be predominantly null. Using the sparse data option, you can instruct SQL Server to not have nulls consume space in sparsely populated fields.

To test this we’re going to delete the Bonus table and then re-create it using the same steps we took previously. The only difference will be that the BonusAmount field will be created using the sparse option. Recall we expect the BonusAmount field to contain very little actual data – most records will be null.

Recall we expect the BonusAmount field to contain very little actual data – most records will be null. The Bonus table now contains 1000 records and BonusAmount is a sparse field, but so far we don’t see any difference in the appearance of the table or the data.

Now let’s review how much space the Bonus table is consuming. Let’s confirm the space usage is less in this example. Had you not used the sparse option the consumption would have been 24KB like in our last example.

Note: If you want to setup the sample JProCo database on your system you can watch this video. For this post you will want to run the SQLArchChapter4.0Setup.sql script from Volume 3.

Question 17

You have two fields, of INT and MONEY, in your Bonus table. You have 1000 records and all instances of the money column are null. When you set up the money field, you used the Sparse option. How much space are the 1000 rows of the money field using?

  1. None
  2. 4000 bytes
  3. 8000 bytes

Do not forget to participate in special question over here: Pluralsight Giving Away Free Subscription to Quiz Participants

Rules:

Please leave your answer in comment section below with correct option, explanation and your country of resident.
Every day one winner will be announced from United States.
Every day one winner will be announced from India.
A valid answer must contain country of residence of answerer.
Please check my facebook page for winners name and correct answer.
Winner from United States will get Joes 2 Pros Volume 3.
Winner from India will get Joes 2 Pros Volume 3.
The contest is open till next blog post shows up at http://blog.sqlauthority.com which is next day GTM+2.5.

Reference:  Pinal Dave (http://blog.SQLAuthority.com)

About these ads

100 thoughts on “SQL SERVER – Tips from the SQL Joes 2 Pros Development Series – Sparse Data and Space Used by Sparse Data – Day 17 of 35

  1. Correct answer is No. 3: The field with MONEY datatype (8 bytes) has been set up using the Sparse option, and all instances are NULL. The field with INT datatype (4 bytes) is fixed-length, so 4 x 1000 is 4000 bytes. Each row has a row header of 4 bytes, so again 4 x 1000 is 4000 bytes. This makes a total of 8000 bytes.
    Rene Castro
    El Salvador

  2. The correct answer is option 1) none.
    1000 rows of the money field which is created using sparse option having the value null takes up no space at all.

    because,
    The SQL Server Database Engine uses the SPARSE keyword in a column definition to optimize the storage of values in that column. Therefore, when the column value is NULL for any row in the table, the value requires no storage.

    Thanks & Regards
    Santosh.S
    Bangalore, India

  3. You save 8000 bytes… From your example 1000 records with sparse option only use 16k as opposed to 24k with sparse option not used. Useful demo thanks

    Matt

    US

  4. Pingback: SQL SERVER – Win a Book a Day – Contest Rules – Day 0 of 35 Journey to SQLAuthority

  5. Correct Answer is # 3.

    MONEY datatype takes up (8 Bytes) and has been set up using the SPARSE option, and all instances (1000) are NULL. SPARSE column does not take storage space for NULL rows.

    INT Datatype is fixed-length and takes (4 Bytes) = 4 * 1000 = 4000 Bytes.
    Each row has a row header of (4 Bytes) = 4 * 1000 = 4000 Bytes.

    So total bytes occupied by “Bonus” table is 8000 Bytes.

    Note: SPARSE option is set only for MONEY column.

    Gopalakrishnan Arthanarisamy
    Unisys, Bangalore, India

  6. Hi,

    Correct answer is Option

    1)None

    explanation :- when “sparse” Used and data in filed is null then is will not take any space in data-base so it is going to be None.

    I am from india.

  7. The correct answer, according to this article, is none (1st option). If all records have NULL in the Money field and we set up our table with SPARSE option, the 1000 rows will use 0 bytes for Money field.

    I am from USA

  8. Correct answer is option 1 that is

    None

    Because here we have used parse option while setting money field.

    Mahmad Khoja
    INDIA
    AHMEDABAD

  9. Option 1) is correct
    1) None

    As you have explained the money field will not contribute to the space used as it is all null with sparse option

    Malay Shah
    India

  10. You have two fields, of INT and MONEY, in your Bonus table. You have 1000 records and all instances of the money column are null. When you set up the money field, you used the Sparse option. How much space are the 1000 rows of the money field using?

    None
    4000 bytes
    8000 bytes

    Solution :

    The correct answer is None. When the money column is created with sparse option and all the 1000 rows are Null then no space is used. This is the property of sparse columns.

    The second and third options are wrong as they indicate some space occupied which doesn’t apply for sparse columns with all Null values.

    Nagaraj Ejanthkar
    USA

  11. option 1 is correct
    because money field is null so it will take no space and you have asked only space used by money field

    tej narayan maurya
    new delhi, india

  12. none that is option one is correct
    because money field is null so it will take no space and you have asked only space used by money field

    tej narayan maurya
    new delhi, india

  13. Correct Ans is 2
    2.) 4000 bytes

    Reson There is 1000 rows and Every row has a 4 byte header because we are using sparse so sparse column datatype size will be not added here

    Abhishek Mishra
    INDIA, NOIDA

  14. option 1.
    if all value for the money column is null then it will not take any space. as the column is defined as sparse.

    ghanshyam
    bangalore

  15. Correct option is: 2
    2. 4000 bytes

    As There are two field int(4 bytes) and money(8 Bytes) and there are total 1000 Rows.
    money field is declared as sparse and it contains null value so it sapce is not added
    So the result is 4(int) * 1000(rows) = 4000 Bytes

    karan,
    India

  16. Hi Sir,

    The correct option is Option No 1 : None

    Money column is created using sparse data option. Which instructs SQL Server to not have nulls consume space in sparsely populated fields.

    So the other two options are not valid in the above question which asks how much space is consumed by the 1000 rows of the money field.

    P.Anish Shenoy,
    INDIA

  17. Correct Answer: 1. None

    Since the column is having Null values, designate it as SPARSE will not consume any space; however not-null values will required additional 4 bytes of storage space along with the normal space required by the data-type.

    Sudeepta,
    India.

  18. Ans is 1. None

    Though money column is as sparse so it will not allocated any space for null.
    Though all thousand column is null so this column will not use any space for storing data..

    Partha
    India

  19. Option 1) is correct
    1) None

    As you have explained the money field will not contribute to the space used as it is all null with sparse option

  20. Correct Option is 1. None.
    Because using the sparse data option, we instruct SQL Server not to have nulls consume space in sparsely populated fields, therefore, when the money field was set up with the Sparse option, 1000 rows of the money field will not use any space.

    (Sale, Nigeria)

  21. Correct Answer is Option 1

    Explanation: As it is described in question that table is created with sparse option for money field. So, it will not consume any space for null values in that field and all the values in that field are NULL. Hence, the space used by 1000 rows of money field is using 0 bytes of space.

    Country – INDIA (Gujarat)

  22. Answer is #1 (none).

    To prove, two tables are set-up: one with non-null int column + sparse money column, another with just the non-null int column. After adding 1000 rows to both, sp_spaceused says they match in size.

    I am from USA.

  23. Correct answer is #1
    NULL = no space used
    Using the sparse data option, you can instruct SQL Server to not have nulls consume space in sparsely populated fields.

    USA

    Mike Michalicek

  24. The table will consume space, but the Money column will not consume any space by itself. Based on the way I read the question, the correct answer should be option 1 None.

    Country: United States

  25. The correct answer is number 1.

    There will be no space consumed since the money field was created with the sparse option and all 1000 records are null.

    Country: USA

  26. If you are using sparse option, and sparse explanation say “Using the sparse data option, you can instruct SQL Server to not have nulls consume space in sparsely populated fields.”

    So, the fields use 0 space.

    The answer is Option 1 : None

    Leonardo

    Country: Chile

  27. Hi Pinal,

    The correct answer for the above question asked is Option #1

    Explanation:

    In the question you asked “How much space are the 1000 rows of the money field using?”

    So we need only the space consumed by the money column as very nicely explained by you that money column with sparse option will never consume any space or no space will be allocated.

    Hence the correct Option is 1 NONE

    Diljeet Kumari
    Country : India

  28. Hi Pinal,

    Challenge:
    Question 17
    You have two fields, of INT and MONEY, in your Bonus table. You have 1000 records and all instances of the money column are null. When you set up the money field, you used the Sparse option. How much space are the 1000 rows of the money field using?

    1.None
    2.4000 bytes
    3.8000 bytes

    Correct Answer:
    The correct answer is the 1st choice: None

    Explanation:
    When you created this Bonus table (for the question), you have two columns, consisting of a column with an INT Data Type and a column with a MONEY Data Type.

    The column with the MoNEY Data Type is using the SPARSE option.

    You have 1000 rows. In every row, the column with the MONEY Data Type contains NULL Values.

    Since you are using the SPARSE option, SQL Server hasn’t assigned or allocated any space for the column with the MONEY Data Type with the SPARSE option, since all rows contain NULL Values for that column.

    Country:
    United States

    Thanks for the knowledge!

    Regards,

    Bill Pepping

  29. option 1 is the ans….none

    when money column is defined as sparse the actual space occupied by money column wont be used as all the values are null….so option1 none is correct

    Dharani

    INDIA

  30. correct answer : 1

    According to this article, is none (1st option). If all records have NULL in the Money field and we set up our table with SPARSE option, the 1000 rows will use 0 bytes for Money field.

    Country : USA

  31. The correct Option for the Question 17 is #1 st option

    Explanation:

    Asked : How much space are the 1000 rows of the money field using?

    Given : We have 1000 records and all instances of the money column are null. When you set up the money field, you used the Sparse option.

    Here we require only the space consumed by the money column as just learned that money column with sparse option will never consume any space or no space will be allocated to it until it has some Data in it.

    Hence the correct Answer is 1 = NONE

    Dilip Kumar Jena
    Country : INDIA

  32. 1. None – sparse fields that are empty consume no space

    Nice article, will be able to use this to save space.

    Thom Boiln
    TX, USA

  33. In Bonus table, 1000 rows of the money sparce column field with NULL data uses none space.

    Answer: 1.None

    SPARSE Keyword in a column definition is used to optimize the storage of values in that column. When the column value is NULL for any row in the table, the value requires no storage.

    Do make a NOTE that “Sparce columns require more storage space for NON-NULL values than the space required for identical data that is not marked SPARSE. For ‘money’ data type required Nonsparse bytes = 8 and Sparse bytes = 12″

    Check out link for estimated space savings by data type: http://msdn.microsoft.com/en-us/library/cc280604.aspx

    Savitur Badhwar
    Los Angeles, CA
    USA

  34. Answer is #1 None.

    Tricky, had to think about that some, but if you are just asking for the amount of space for that column which has all nulls and not the entire table, then the answer would have to be none since SPARSE was used.

    USA

    Hope I’m not too late, my post from earlier today isn’t in the list (I must have forgotten to click post?) I just remember that I forgot my country and came back in.

  35. You have two fields, of INT and MONEY, in your Bonus table. You have 1000 records and all instances of the money column are null. When you set up the money field, you used the Sparse option. How much space are the 1000 rows of the money field using?

    None
    4000 bytes
    8000 bytes

    Solution :

    The correct answer is None. When the money column is created with sparse option and all the 1000 rows are Null then no space is used. This is the property of sparse columns.

    The second and third options are wrong as they indicate some space occupied which doesn’t apply for sparse columns with all Null values.

    Sreeram
    Indian

  36. Hi Pinal,
    The correct answer is option 1 which is None.

    Ques:-You have ask how much space is used by the money column when sparse is used in the Bonus table?
    Explanation:-Already you have mentioned in the blog that when any column which contains NULL values of a table if sparse is applied then we are instructing SQL Server to not consume space .

    Thanks,
    Manik Dey
    India

  37. Answer::: 3 (8000 bytes)

    here we have two fields one INT and money( sparce)
    so here 1000 rows inserted, and money is null
    so each row take 4 bytes(header)+4 bytes(Int)+0(money sparse)=8 bytes
    total rows=1000
    total space=1000* 8=8000 bytes

  38. Answer::: 3 (8000 bytes)

    here we have two fields one INT and money( sparce)
    so here 1000 rows inserted, and money is null
    so each row take 4 bytes(header)+4 bytes(Int)+0(money sparse)=8 bytes
    total rows=1000
    total space=1000* 8=8000 bytes

    thanks,
    Bhasker, USA

  39. Answer: 1
    The correct answer is none (1st option). If all records have NULL in the Money field and if table column set up with SPARSE option, the 1000 rows will use 0 bytes for Money field.

    Country: India

  40. Hello

    believe answer 1 (none) is the correct choice here. The money field will not add to the space used because it is a null with sparse option

    Eric
    (USA)

  41. Answer: Option 1

    But the nulls in the money field do not change the space consumption,
    because fixed length data types always use the full amount of space allocated to them.

    Without Sparse:
    ——————–
    CREATE TABLE BONUS
    (
    BONUS_ID INT NOT NULL,
    BONUS_AMOUNT MONEY NULL
    )
    GO

    DECLARE @ID INT
    SET @ID = 1
    WHILE @ID <= 1000
    BEGIN
    INSERT INTO BONUS VALUES (@ID, NULL)
    SET @ID = @ID + 1
    END
    GO

    EXEC sp_spaceused 'BONUS'

    OUTPUT: BONUS 1000 23688 KB 23680 KB 8 KB 0 KB

  42. Pingback: SQL SERVER – SSQL Architecture Basics – Core Architecture Concepts – Book Available for SQL Server Certification Journey to SQLAuthority

  43. Pingback: SQL SERVER – Clustered Index and Primary Key – Contest Win Joes 2 Pros Combo (USD 198) – Day 3 of 5 « SQL Server Journey with SQL Authority

  44. Pingback: SQL SERVER – Weekly Series – Memory Lane – #042 | Journey to SQL Authority with Pinal Dave

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s