Dear Dev,In the world of SQL Server, partitioning is a way to divide large tables and indexes into smaller, more manageable pieces. It can improve query performance, manageability, and availability. In this article, we will take a closer look at what partitioning is and how it works in SQL Server.
Partitioning Overview
In SQL Server, partitioning is a way to divide tables and indexes into smaller, more manageable pieces. Each partition is stored separately and can be managed independently. This allows for more efficient data retrieval and can help improve query performance.
Partitioning can be done on a single table or index, or across multiple tables or indexes. It can be based on a range of values, such as dates or numbers, or on a hash function that distributes data evenly across partitions.
Partitioning is especially useful for large data warehouses or databases that handle a high volume of transactions. By dividing data into smaller chunks, partitioning can make it easier to manage, backup, and restore data.
How Partitioning Works
When you partition a table or index in SQL Server, you are essentially creating a set of smaller tables or indexes that are grouped together. Each partition has its own set of data pages and storage locations, and can be indexed separately.
When a query is submitted to the database, SQL Server will determine which partition(s) contain the data that is needed. This allows for more efficient retrieval of data, since the database only needs to access the partitions that contain the requested data.
Partitioning can also improve query performance by allowing for more effective use of parallel processing. By dividing data into smaller chunks, SQL Server can process queries across multiple cores or processors more efficiently.
Partitioning Types
There are several types of partitioning in SQL Server:
Partitioning Type |
Description |
|---|---|
Range Partitioning |
Divides data based on a range of values, such as dates or numbers. |
List Partitioning |
Divides data based on a list of values, such as product IDs or customer names. |
Hash Partitioning |
Distributes data evenly across partitions based on a hash function. |
Composite Partitioning |
Uses a combination of range, list, or hash partitioning to divide data. |
Range Partitioning
Range partitioning is the most common type of partitioning in SQL Server. It divides data into partitions based on a range of values. For example, you could partition a table of sales data based on the date of the sale:
CREATE PARTITION FUNCTION SalesByDate (datetime)
AS RANGE LEFT FOR VALUES ('2017-01-01', '2018-01-01', '2019-01-01')
This creates a partition function that divides the data into three partitions based on the date of the sale. The partitions are defined by the values ‘2017-01-01’, ‘2018-01-01’, and ‘2019-01-01’. Any sales before ‘2017-01-01’ will be stored in the first partition, any sales between ‘2017-01-01’ and ‘2018-01-01’ will be stored in the second partition, and so on.
You can then create a partition scheme that maps the partitions to physical filegroups:
CREATE PARTITION SCHEME SalesByDateScheme
AS PARTITION SalesByDate
TO (Sales_2016, Sales_2017, Sales_2018, Sales_2019)
This creates a partition scheme that maps the partitions defined in the SalesByDate partition function to physical filegroups. This allows you to store each partition on a separate disk, improving performance and manageability.
List Partitioning
List partitioning divides data based on a list of values. For example, you could partition a table of customer data based on the state where the customer lives:
CREATE PARTITION FUNCTION CustomersByState (varchar(2))
AS LIST
(
'AL', 'AK', 'AZ', 'AR', 'CA', 'CO', 'CT', 'DE', 'FL', 'GA', 'HI', 'ID', 'IL', 'IN', 'IA', 'KS', 'KY', 'LA', 'ME', 'MD', 'MA', 'MI', 'MN', 'MS', 'MO', 'MT', 'NE', 'NV', 'NH', 'NJ', 'NM', 'NY', 'NC', 'ND', 'OH', 'OK', 'OR', 'PA', 'RI', 'SC', 'SD', 'TN', 'TX', 'UT', 'VT', 'VA', 'WA', 'WV', 'WI', 'WY'
)
This creates a partition function that divides the data into partitions based on the state where the customer lives. The partitions are defined by the list of values in the partition function.
You can then create a partition scheme that maps the partitions to physical filegroups:
CREATE PARTITION SCHEME CustomersByStateScheme
AS PARTITION CustomersByState
TO (Customer_West, Customer_Midwest, Customer_Northeast, Customer_South)
This creates a partition scheme that maps the partitions defined in the CustomersByState partition function to physical filegroups. This allows you to store each partition on a separate disk, improving performance and manageability.
Hash Partitioning
Hash partitioning distributes data evenly across partitions based on a hash function. This is useful when you want to distribute data evenly across a large number of partitions.
To create a hash-partitioned table, you first need to create a partition function that specifies the number of partitions:
CREATE PARTITION FUNCTION HashPartitions (int)
AS HASH (ProductId)
WITH (BUCKET_COUNT = 16)
This creates a partition function that divides the data into 16 partitions based on the hash value of the ProductId column. The WITH (BUCKET_COUNT = 16) option specifies that there are 16 partitions.
You can then create a partition scheme that maps the partitions to physical filegroups:
CREATE PARTITION SCHEME HashPartitionsScheme
AS PARTITION HashPartitions
TO (Data_01, Data_02, Data_03, Data_04, Data_05, Data_06, Data_07, Data_08, Data_09, Data_10, Data_11, Data_12, Data_13, Data_14, Data_15, Data_16)
This creates a partition scheme that maps the partitions defined in the HashPartitions partition function to physical filegroups. This allows you to store each partition on a separate disk, improving performance and manageability.
Composite Partitioning
Composite partitioning uses a combination of range, list, or hash partitioning to divide data. For example, you could partition a table of sales data based on the date of the sale and the state where the sale occurred:
CREATE PARTITION FUNCTION SalesByDateState (datetime)
AS RANGE LEFT FOR VALUES ('2017-01-01', '2018-01-01', '2019-01-01')
CREATE PARTITION FUNCTION SalesByState (varchar(2))
AS LIST (
'AL', 'AK', 'AZ', 'AR', 'CA', 'CO', 'CT', 'DE', 'FL', 'GA', 'HI', 'ID', 'IL', 'IN', 'IA', 'KS', 'KY', 'LA', 'ME', 'MD', 'MA', 'MI', 'MN', 'MS', 'MO', 'MT', 'NE', 'NV', 'NH', 'NJ', 'NM', 'NY', 'NC', 'ND', 'OH', 'OK', 'OR', 'PA', 'RI', 'SC', 'SD', 'TN', 'TX', 'UT', 'VT', 'VA', 'WA', 'WV', 'WI', 'WY'
)
CREATE PARTITION SCHEME SalesByDateStateScheme
AS PARTITION SalesByDateState
TO (Sales_2016, Sales_2017, Sales_2018, Sales_2019), Sales_West, Sales_Midwest, Sales_Northeast, Sales_South)
This creates a partition function that divides the data into partitions based on the date of the sale and the state where the sale occurred. The partitions are defined by the values in the partition functions.
You can then create a partition scheme that maps the partitions to physical filegroups:
CREATE PARTITION SCHEME SalesByDateStateScheme
AS PARTITION SalesByDateState
TO (Sales_2016, Sales_2017, Sales_2018, Sales_2019), Sales_West, Sales_Midwest, Sales_Northeast, Sales_South
This creates a partition scheme that maps the partitions defined in the SalesByDateState partition function to physical filegroups. This allows you to store each partition on a separate disk, improving performance and manageability.
FAQ
Why should I use partitioning in SQL Server?
Partitioning can help improve performance, manageability, and availability of large tables and indexes in SQL Server. By dividing data into smaller chunks, partitioning can make it easier to manage, backup, and restore data. It can also improve query performance by allowing for more efficient data retrieval and parallel processing.
What are the different types of partitioning in SQL Server?
The different types of partitioning in SQL Server are range partitioning, list partitioning, hash partitioning, and composite partitioning. Each type of partitioning is used to divide data in a different way, based on a range of values, a list of values, a hash function, or a combination of these methods.
How do I create a partitioned table in SQL Server?
To create a partitioned table in SQL Server, you need to define a partition function that specifies how the data should be divided, and a partition scheme that maps the partitions to physical filegroups. You can then create the table and specify the partition scheme as part of the table definition.
How do I maintain a partitioned table in SQL Server?
To maintain a partitioned table in SQL Server, you need to be aware of the partitioning scheme and how data is distributed across partitions. You may need to rebuild indexes, update statistics, or merge or split partitions periodically to maintain performance and manageability.
Can I convert an existing table to a partitioned table in SQL Server?
Yes, you can convert an existing table to a partitioned table in SQL Server using the ALTER TABLE statement. However, this process can be time-consuming and may require downtime or other special considerations. It is best to plan for partitioning from the beginning of a project or when designing a new table.
In conclusion, partitioning is an important feature of SQL Server that can help improve performance, manageability, and availability of large tables and indexes. By dividing data into smaller chunks, partitioning can make it easier to manage, backup, and restore data. It can also improve query performance by allowing for more efficient data retrieval and parallel processing. We hope this article has given you a better understanding of what partitioning is and how it works in SQL Server.