What is the concept of partitioning in databases and its advantages?

Partitioning a database entails splitting a large database into more manageable, smaller segments known as partitions. This segmentation is performed based on several strategies such as range, list, hash, and composite partitioning, each dictating the way data is divided.

Let’s take a look at each with some SQL code:

Range partitioning

Here, the database is segmented according to a specific range. For instance, an ‘Orders’ table could be partitioned by order dates. When a new order is inserted, it automatically goes into the partition that corresponds to its order date. Similarly, when an order’s date is updated, it is managed within the same partition or moved to a different one, depending on the database system.

CREATE TABLE Orders
(
  OrderID int NOT NULL,
  OrderDate date NOT NULL,
  ...
)
PARTITION BY RANGE (OrderDate);

-- Creating partitions
CREATE TABLE Orders_2019 PARTITION OF Orders FOR VALUES FROM ('2019-01-01') TO ('2020-01-01');
CREATE TABLE Orders_2020 PARTITION OF Orders FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');

List partitioning

Data is divided according to a list of values. For example, a ‘Customers’ table could be partitioned by city names. Updates or inserts to the customer’s city will automatically place the data into the appropriate partition.

CREATE TABLE Customers
(
  CustomerID int NOT NULL,
  City varchar(255) NOT NULL,
  ...
)
PARTITION BY LIST (City);

-- Creating partitions
CREATE TABLE Customers_NewYork PARTITION OF Customers FOR VALUES IN ('New York');
CREATE TABLE Customers_LosAngeles PARTITION OF Customers FOR VALUES IN ('Los Angeles');

Hash partitioning

A hash function is used for partitioning the data, providing a balanced distribution of data. Any inserts or updates are automatically reflected in the appropriate hash partition.

CREATE TABLE Products
(
  ProductID int NOT NULL,
  ...
)
PARTITION BY HASH (ProductID);

-- Creating partitions
CREATE TABLE Products_Part1 PARTITION OF Products FOR VALUES WITH (MODULUS 4, REMAINDER 0);
CREATE TABLE Products_Part2 PARTITION OF Products FOR VALUES WITH (MODULUS 4, REMAINDER 1);

Composite partitioning

This is a mix of other partitioning types. A database could be initially range-partitioned, and then each range could be hash-partitioned.

When data is inserted or updated, it is automatically directed to the correct partition. The database management system handles this behind the scenes. However, if an update operation changes the partition key value, how this is handled can vary between different databases. In some, like PostgreSQL, it’s not permitted and would cause an error. In others like Oracle and SQL Server, the row is moved from the old partition to the new one, which can be an intensive operation.

Benefits of partitioning include improved performance, more efficient data management, parallelism, better data distribution, and enhanced availability. However, it’s important to use partitioning wisely, considering the nature of your data and your query needs. It’s typically more beneficial for larger databases, while the overhead might not be worthwhile for smaller ones.