SQL Server Partitioning Tables: A Comprehensive Guide for Dev

Hello Dev, welcome to our guide on SQL Server Partitioning Tables. In this article, we will discuss everything you need to know about partitioning tables in SQL Server. We will cover the basics of partitioning, how it works, and the benefits it provides. So, let’s get started!

What is partitioning?

Partitioning is a database design technique that divides large tables into smaller, more manageable pieces. Each piece is called a partition and is stored separately on disk. Partitioning helps to improve performance, availability, and manageability of large tables.

How does partitioning work?

When a table is partitioned, it is divided into smaller sections based on a partition key. The partition key determines how the data is distributed across the partitions. Each partition is stored in a separate filegroup or partition scheme on disk.

When a query is executed against a partitioned table, SQL Server only reads the data from the relevant partitions. This improves query performance and reduces disk I/O. Partitioning also makes it easier to maintain and backup large tables.

What are the benefits of partitioning?

Partitioning provides several benefits, including:

Benefits	Description
Improved Performance	Queries are faster because SQL Server reads only the relevant partitions.
Increased Availability	Partitions can be moved or rebuilt without impacting the entire table.
Better Manageability	Partitions can be easily managed and maintained.
Reduced Backup Times	Partitions can be backed up individually, reducing backup times.

Types of Partitioning

There are several types of partitioning available in SQL Server:

1. Range Partitioning

Range partitioning divides data into partitions based on a range of values. For example, a table can be partitioned based on the date column, where each partition contains data for a specific date range.

2. Hash Partitioning

Hash partitioning divides data into partitions based on a hash function. Each partition contains roughly the same number of rows, making it useful for distributing data uniformly across disks.

3. List Partitioning

List partitioning divides data into partitions based on a list of values. For example, a table can be partitioned based on the region column, where each partition contains data for a specific region.

Partitioning Keys

The partitioning key determines how the data is distributed across partitions. It can be any column or combination of columns in the table. The partitioning key must be a part of the primary key, unique constraint, or clustered index of the table.

How to Create a Partitioned Table?

Creating a partitioned table in SQL Server involves several steps:

1. Create a Partition Function

A partition function defines how the data is partitioned based on the partitioning key. It maps each value in the partitioning key to a partition number. For example, a partition function can be created to partition a table based on a date column:

CREATE PARTITION FUNCTION DatePartition (datetime)AS RANGE RIGHT FOR VALUES ('2015-01-01', '2016-01-01', '2017-01-01');

2. Create a Partition Scheme

A partition scheme maps partitions to filegroups or partition schemes on disk. It specifies where each partition is stored. For example, a partition scheme can be created to store partitions 1-3 in filegroup FG1 and partitions 4-6 in filegroup FG2:

CREATE PARTITION SCHEME DateSchemeAS PARTITION DatePartitionTO (FG1, FG2);

3. Create a Table with Partitioning

A table can be created with partitioning by specifying the partition scheme and partitioning key:

CREATE TABLE Sales(SalesDate datetime,Amount money,CONSTRAINT PK_Sales PRIMARY KEY CLUSTERED (SalesDate))ON DateScheme (SalesDate);

How to Manage Partitions?

Managing partitions involves several operations, such as adding, splitting, merging, and moving partitions. SQL Server provides several commands and functions to manage partitions:

1. ALTER PARTITION FUNCTION

This command is used to modify the partition function. For example, to add a new partition to the DatePartition function:

ALTER PARTITION FUNCTION DatePartition ()SPLIT RANGE ('2018-01-01');

2. ALTER PARTITION SCHEME

This command is used to modify the partition scheme. For example, to add a new filegroup to the DateScheme:

ALTER PARTITION SCHEME DateSchemeNEXT USED FG3;

3. ALTER TABLE

This command is used to modify the partitioning of a table. For example, to move a partition from one filegroup to another:

ALTER TABLE SalesSWITCH PARTITION 4 TO SalesFG4;

FAQ

1. Can I partition an existing table?

Yes, you can partition an existing table by creating a new partitioned table and then copying the data into it. You can also use the “CREATE CLUSTERED INDEX” statement to create a partitioned index on an existing table.

2. Can I partition a non-clustered index?

Yes, you can partition a non-clustered index by creating a partitioned index on the table.

3. What is the minimum and maximum number of partitions allowed?

The minimum number of partitions allowed is 1, and the maximum number of partitions allowed is 15,000.

4. What is the difference between horizontal partitioning and vertical partitioning?

Horizontal partitioning divides a table into smaller pieces based on the rows. It is also known as sharding. Vertical partitioning divides a table into smaller pieces based on the columns.

5. How does partitioning affect performance?

Partitioning can improve performance by reducing the amount of data that needs to be scanned to answer a query. It can also improve parallelism by allowing queries to be executed across multiple partitions at the same time.

Conclusion

Partitioning is a powerful database design technique that can help to improve performance, availability, and manageability of large tables. SQL Server provides several types of partitioning and tools to manage partitions. With this guide, you should now have a better understanding of partitioning and how to implement it in SQL Server. Happy partitioning!