non-clustered index part 1 (B-tree index)
Tags: postgressql, apacheage
Published: 2023-07-01 02:14:12

In PostgreSQL, a non-clustered index is a data structure that improves the performance of queries by providing faster access to specific data within a table. It is called "non-clustered" because the physical order of the data in the table is not modified to match the index.
When creating a non-clustered index in PostgreSQL, it's important to note that by default, the index is automatically created as a B-tree index.

**What is B-tree index ?**

In PostgreSQL, a B-tree index is the default and most commonly used type of non-clustered index. It provides efficient searching, insertion, and deletion operations on indexed columns. Here's an explanation of B-tree indexes and a use case for their application:

**B-tree Index in PostgreSQL:**

A B-tree index is a balanced tree structure where index entries are stored in sorted order. Each level of the tree consists of pages, and the index entries are distributed across these pages. The root page serves as the entry point to the index, and subsequent levels branch out until the leaf pages are reached, containing the actual index entries along with pointers to the corresponding table rows.
B-tree indexes in PostgreSQL have the following characteristics:

**1.Balanced Structure:** B-trees are balanced trees, which means that the depth of the tree is minimized, leading to efficient search operations. The number of levels in the tree remains relatively small, allowing for fast traversal and retrieval of data.

**2.Sorted Entries:** The entries within each level of the B-tree index are stored in a sorted order based on the indexed column(s). This sorted structure enables efficient range queries, equality searches, and sorting operations.

**3.Adaptive Split and Merge:** B-trees in PostgreSQL dynamically adapt to changes in data distribution and automatically perform split and merge operations to maintain balance. This adaptability ensures that the index remains efficient even as data is inserted, updated, or deleted.

**4.Multi-column Indexing:** B-tree indexes can be created on one or more columns in PostgreSQL. This allows for optimizing queries involving multiple columns by leveraging the combined sorting capabilities of the index.

**Use Case for B-tree Indexes:**

A common use case for B-tree indexes is optimizing queries involving range conditions or equality searches. Here's an example:

Let's consider a scenario where you have a PostgreSQL database containing a table named "Orders" with millions of records. The "Orders" table has a column named "order_date" that stores the date of each order.

To optimize queries that involve filtering by a specific date range or retrieving orders sorted by the order date, you can create a B-tree index on the "order_date" column:

```
CREATE INDEX idx_order_date ON Orders (order_date);

```
With this B-tree index in place, queries such as the following can benefit from its usage:

1.Retrieve all orders placed between a specific date range:
```
SELECT * FROM Orders WHERE order_date >= '2023-01-01' AND order_date <= '2023-06-30';

```
2.Retrieve orders sorted by the order date:

```
SELECT * FROM Orders ORDER BY order_date;

```
The B-tree index allows PostgreSQL to efficiently navigate the index tree structure, quickly locating the relevant index entries and retrieving the corresponding rows. It significantly improves the performance of these queries, especially when dealing with large datasets.

**In summary**, B-tree indexes in PostgreSQL are well-suited for optimizing range queries, equality searches, and sorting operations. They provide fast access to data based on the indexed columns' values and are widely applicable in scenarios where efficient data retrieval and filtering are essential.