Speed up your query in Postgres
Tags: database
Published: 2023-07-03 06:22:17

## Table of contents

- [Indexing](#indexing)
- [Use EXPLAIN ANALYZE](#use-explain-analyze)
- [Use UNION Instead of OR to Use Index](#use-union-instead-of-or-to-use-index)
- [Use EXISTS Instead of JOIN to Prevent Duplicating](#use-exists-instead-of-join-to-prevent-duplicating)
- [Optimize Your Query Structure](#optimize-your-query-structure)
- [Use Materialized view](#use-materialized-view)
- [Use Appropriate Data Types](#use-appropriate-data-types)
- [Limit the Amount of Data Retrieved](#limit-the-amount-of-data-retrieved)

## Indexing

An index is a data structure that improves the speed of data retrieval operations on a database table. It works similarly to an index in a book - instead of scanning the entire book to find a particular topic, you can go to the index, find the page number, and go directly to that page. 

In PostgreSQL, you can create an index on any column in your table. However, it's important to note that while indexes speed up data retrieval, they slow down data modification operations like `INSERT`, `UPDATE`, and `DELETE`. Therefore, you should only index the columns that you frequently use in your `WHERE` clauses.


### Some index types that're supported in postreges:
1. **B-Tree Indexes**: This is the default index type in PostgreSQL. It's useful for equality and range queries. B-Tree indexes can handle any sort of comparison operators such as <, <=, =, >=, >, and BETWEEN.

2. **Hash Indexes**: These indexes are best for equality comparisons. They're faster than B-Tree indexes for these types of comparisons, but they can't be used for range queries.

3. **GiST (Generalized Search Tree) Indexes**: These are particularly useful for multidimensional data types and full-text search. They're very flexible and can be used for a wide variety of queries.

4. **GIN (Generalized Inverted Index) Indexes**: These are best for indexing composite types and arrays. They're particularly useful when you have queries that involve multiple elements in an array.

5. **SP-GiST (Space-Partitioned Generalized Search Tree) Indexes**: These are useful for data that can be naturally divided into non-overlapping regions, such as geometrical data.

6. **BRIN (Block Range INdex) Indexes**: These are best for very large tables where certain ranges of values are stored together. They're very space-efficient and offer good performance for range queries.

7. **Partial Indexes**: These indexes only index the rows that satisfy the specified WHERE clause. They can be very efficient if you often run queries that involve a subset of your data.

Remember, the best index type for your use case depends on the nature of your data and the queries you're running. It's often a good idea to experiment with different index types and use the `EXPLAIN ANALYZE` command to see which one offers the best performance.## 2. Partitioning

Partitioning is another effective way to improve the performance of PostgreSQL databases. It involves splitting a large table into smaller, more manageable pieces called partitions. Each partition is a separate table that stores a subset of the data.

Partitioning can significantly reduce the amount of time it takes to fetch data from a table. When a query is executed, PostgreSQL only scans the relevant partition(s), rather than the entire table. This can be particularly beneficial for large tables with billions of rows.


## Use EXPLAIN ANALYZE

`EXPLAIN ANALYZE` is a powerful tool in PostgreSQL that helps you understand how your query is executed and where you can optimize it. It provides detailed information about the execution plan of your query, including:
- Query Execution Time: The total time taken to execute the query, including both planning and execution phases.
- Planning Time: The time taken for the query planner to generate the execution plan.
- Execution Time: The time taken to execute the query plan.
- Number of Rows: The number of rows processed or affected by each step in the query plan.
- Cost: The estimated cost of executing each step in the query plan.
- Operations: The specific operations performed by the query plan, such as index scans, sequential scans, joins, and aggregations.
- Scan Types: The type of scan used to access tables or indexes, including sequential scans, index scans, bitmap scans, and index-only scans.
- Filter Conditions: Any filter conditions applied to restrict the result set.
- Sort Information: Details about sorting operations, including the sort method and the estimated and actual number of sorted rows.
- etc.

## Use UNION Instead of OR to Use Index

When you're dealing with multiple conditions in your queries, using `UNION` instead of `OR` can help you take advantage of your indexes. When you use `OR`, PostgreSQL has to scan the entire table to find the rows that match either condition. On the other hand, when you use `UNION`, PostgreSQL can use an index to find the rows that match each condition separately, and then combine the results.

## Use EXISTS Instead of JOIN to Prevent Duplicating

Sometimes, you only need to check if a certain condition is met, without actually retrieving the data. In such cases, using `EXISTS` instead of `JOIN` can speed up your queries. The `EXISTS` operator returns a boolean value indicating whether a subquery returns any row. It stops processing as soon as it finds a matching row, which can be much faster than a `JOIN` that has to process all rows.

## Optimize Your Query Structure

The way you structure your SQL queries can also impact their performance. For example, using subqueries in the `FROM` clause can slow down your query because it forces PostgreSQL to create a temporary table for the subquery. Instead, try to use subqueries in the `WHERE` or `SELECT` clause, where PostgreSQL can optimize them.

## Use Materialized view
If you're handing the queries that involve complex calculations, aggregations, or joins on large tables, and do not require real-time data, materialized view could be the ideal solution for you.
A materialized view is a precomputed snapshot of a query result that is stored as a physical table in the database. Unlike regular views, which execute the underlying query every time they are referenced, materialized views persist the result set, providing faster access to the data. This caching mechanism is particularly useful when dealing with large datasets that are relatively static or require infrequent updates.


## Use Appropriate Data Types

Using the appropriate data types for your columns can also improve query performance. For example, if a column contains only integer values, it's more efficient to use the `INTEGER` data type than the `VARCHAR` data type. PostgreSQL has a variety of data types, including numeric, string, and date/time data types, so you can choose the one that best fits your data.

## Limit the Amount of Data Retrieved

If you don't need to retrieve all the data from a table, don't. Use the `LIMIT` clause to restrict the number of rows returned by your query. This can significantly reduce the amount of data that PostgreSQL needs to process, resulting in faster queries.