This blog was first authored in 2024 and we’ve updated it in 2025 for clarity and relevance, reflecting current practices while honoring the original perspective.
PostgreSQL is known for its reliability and feature-rich environment, but as with any database, when datasets grow larger and query complexity increases, efficient data retrieval becomes crucial for maintaining optimal database performance. This is where indexes play a vital role, enhancing performance by allowing for faster data retrieval.
Indexes are data structures that store a subset of data from a table in a form that allows for quicker access. PostgreSQL provides various indexing techniques tailored for different data types and use cases.
This blog aims to provide a comprehensive resource for understanding and optimizing indexes in PostgreSQL. It covers the different index types, their use cases, and performance implications. By the end, you’ll be equipped to utilize indexes strategically and significantly improve query performance and overall database efficiency.
Understanding PostgreSQL indexes
Indexes in PostgreSQL are special data structures that store a portion of the table’s data in a way that speeds up data retrieval. A common comparison is that they function like an index in a book, allowing the database to quickly locate and access the rows associated with a particular query.
How PostgreSQL stores and accesses data
PostgreSQL stores data in a structured format within tables, and when a query is executed, PostgreSQL scans these tables to find the relevant data. Without indexes, this can mean scanning every row in a table, which becomes inefficient as the dataset grows. Indexes help by creating a smaller, searchable subset of the data that PostgreSQL can use to speed up queries.
PostgreSQL supports several types of indexes, each tailored for specific use cases and data types. We will go into these more in-depth in the next section, but here is a brief overview of the main types:
- B-tree indexes: The most common type, ideal for equality and range queries.
- Hash indexes: Suitable for simple equality comparisons.
- GiST (Generalized Search Tree): Flexible and supports a variety of custom data types and complex queries.
- GIN (Generalized Inverted Index): Designed for indexing composite values, such as arrays or full-text search.
- BRIN (Block Range INdexes): Efficient for large tables with naturally sorted data.
- SP-GiST (Space-partitioned Generalized Search Tree): Optimized for data that can be partitioned into non-overlapping regions, useful for multidimensional data.
Benefits of using indexes
Indexes significantly improve query performance by reducing the amount of data PostgreSQL needs to scan. This results in faster data retrieval, particularly for complex queries and large datasets. Additionally, indexes can help with:
- Reducing I/O operations: Minimizes the number of disk accesses required to retrieve data.
- Enhancing sorting and filtering operations: Speeds up queries that involve ORDER BY and WHERE clauses.
- Supporting unique constraints: Enforces data integrity by ensuring the uniqueness of column values.
- Optimizing join operations: Improves the efficiency of queries that join multiple tables by quickly locating matching rows.
- Facilitating index-only scans: Allows queries to be satisfied using only the index, avoiding table access.
- Improving aggregation queries: Speeds up operations involving aggregate functions by quickly narrowing down the data set.
Types of indexes in PostgreSQL
Now that we have the basics down let’s explore the different types of indexes in PostgreSQL a little more in-depth and look at some example queries.
B-tree indexes
B-tree indexes are the default and most commonly used index type in PostgreSQL. They are well-suited for a wide range of queries, including equality and range queries. B-tree indexes maintain sorted data, making them efficient for retrieving ordered data.
Example queries:
Creating a B-tree index:
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CREATE INDEX idx_employee_name ON employees (name); |
Using the B-tree index in a query:
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SELECT * FROM employees WHERE name = 'John Doe'; |
Hash indexes
Hash indexes are used for simple equality comparisons. They are faster than B-tree indexes for such operations but have limitations, such as not supporting range queries. Additionally, hash indexes are not WAL-logged, which means they are not crash-safe and are best used in read-heavy environments where data integrity can be managed differently.
Example queries:
Creating a hash index:
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CREATE INDEX idx_employee_id_hash ON employees USING hash (employee_id); |
Using the hash index in a query:
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SELECT * FROM employees WHERE employee_id = 12345; |
GIN (Generalized Inverted Index)
GIN indexes are designed for indexing composite values, such as arrays or full-text searches. They are efficient for operations that involve searching for elements within these composite types.
Example queries:
Creating a GIN index for full-text search:
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CREATE INDEX idx_document_content ON documents USING gin (to_tsvector('english', content)); |
Using the GIN index in a query:
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SELECT * FROM documents WHERE to_tsvector('english', content) @@ to_tsquery('database'); |
GiST (Generalized Search Tree)
GiST indexes provide a framework for creating custom indexing strategies. They are versatile and can be used for various data types, including geometric data and full-text search.
Example queries:
Creating a GiST index for geometric data:
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CREATE INDEX idx_location_geom ON locations USING gist (geom); |
Using the GiST index in a query:
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SELECT * FROM locations WHERE ST_DWithin(geom, ST_MakePoint(-77.0364, 38.8951)::geography, 1000); |
SP-GiST (Space-partitioned Generalized Search Tree)
SP-GiST indexes are optimized for data that can be partitioned into non-overlapping regions, making them useful for multidimensional data such as spatial and network data.
Example queries:
Creating an SP-GiST index:
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CREATE INDEX idx_network_path ON network_paths USING spgist (path); |
Using the SP-GiST index in a query:
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SELECT * FROM network_paths WHERE path @> '192.168.1.0/24'; |
BRIN (Block Range INdexes)
BRIN indexes are efficient for large tables where data is naturally ordered or clustered. They store summary information about block ranges, making them very space-efficient and suitable for scenarios where precise indexing is not required.
Example queries:
Creating a BRIN index:
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CREATE INDEX idx_huge_table_date ON huge_table USING brin (date); |
Using the BRIN index in a query:
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SELECT * FROM huge_table WHERE date BETWEEN '2023-01-01' AND '2023-12-31'; |
Each of these index types in PostgreSQL is tailored for specific use cases, and understanding their strengths and limitations can help you select the right type for your queries and data.
Index maintenance and monitoring
Over time, as data is inserted, updated, and deleted, indexes can become fragmented and less efficient. Regular maintenance helps keep indexes in good condition, ensuring they continue to speed up query performance rather than hinder it. Proper index maintenance can prevent performance degradation, reduce I/O operations, and maintain the overall health of your PostgreSQL database. Monitoring index performance is a key part of this maintenance process, allowing you to identify and address issues before they impact performance.
Monitoring index performance
Monitoring index performance involves regularly checking their usage and efficiency. PostgreSQL provides several tools and commands to help you understand how well your indexes are performing:
- pg_stat_user_indexes: This system view provides statistics about index usage.
- pg_stat_all_indexes: Similar to pg_stat_user_indexes, but includes system indexes.
- pg_statio_user_indexes: This view gives information about I/O operations related to indexes.
In addition to these built-in tools, Percona Monitoring and Management (PMM) provides a comprehensive solution for monitoring and managing PostgreSQL indexes. PMM offers detailed insights into index usage, performance metrics, and potential issues, allowing you to maintain and optimize your database proactively.
Maintenance tools and commands
PostgreSQL offers several commands and tools to maintain and optimize indexes:
REINDEX: This command rebuilds an index, helping to remove fragmentation and improve performance. It’s useful when an index has become bloated due to heavy insertions, updates, or deletions.
VACUUM: While primarily used to reclaim storage by removing dead tuples, the VACUUM command also updates index statistics, helping the query planner make better decisions.
Related: PostgreSQL Vacuuming Command to Optimize Database Performance
ANALYZE: This command collects statistics about the contents of tables and indexes. These statistics are used by the query planner to optimize query performance. Regularly running ANALYZE ensures the planner has up-to-date information.
By incorporating these practices into your database management routine, you can maintain the health of your indexes and ensure they continue to provide the performance benefits they are designed for. Using tools like Percona Monitoring and Management can further enhance your ability to monitor, manage, and optimize indexes, ensuring a high-performance database environment.
Advanced indexing techniques
To further optimize your PostgreSQL queries, advanced indexing techniques can be employed. These techniques go beyond basic indexing, offering powerful tools to handle complex queries and improve overall database performance. Here, we explore several key strategies to enhance your indexing approach.
Covering indexes
Covering indexes are designed to include all the columns required by a query, allowing the database to retrieve all the needed data from the index itself without having to access the table. This can significantly reduce I/O operations and improve query performance. By carefully selecting the columns to be included in the index, covering indexes can be a powerful tool for optimizing read-heavy workloads.
Index-only scans
Index-only scans are a performance optimization that enables PostgreSQL to satisfy a query using only the index without accessing the table. This is particularly beneficial for queries where the indexed columns provide all the necessary information. Index-only scans reduce the number of I/O operations, leading to faster query execution times. This technique works best when the index is highly selective, and the data in the index is frequently updated to reflect the latest changes.
Combining multiple indexes for complex queries
For complex queries, combining multiple indexing strategies can yield significant performance improvements. Here are some advanced techniques for indexing:
- Filtered indexes: These indexes are created on a subset of rows based on a specific condition. They are useful for scenarios where queries frequently filter on certain criteria, reducing the size of the index and improving performance.
- Expression indexes: These indexes are built on expressions or functions applied to one or more columns. They are helpful when queries often involve calculations or transformations on column values, enabling faster retrieval of the computed results.
- Indexing JSON/JSONB data: PostgreSQL provides robust support for JSON and JSONB data types. Indexing these data types can significantly enhance performance when querying JSON documents. GIN indexes are particularly effective for indexing JSONB data, allowing efficient search operations within JSON documents.
- Indexing for full-text search with GIN indexes: GIN indexes are well-suited for full-text search operations. They allow efficient indexing and querying of text data, making them ideal for applications that require searching large volumes of textual information.
- Indexing for spatial data types with SP-GiST indexes: SP-GiST indexes are optimized for spatial data types, such as geographic and geometric data. They enable efficient indexing and querying of spatial data, making them valuable for applications that require complex spatial queries and operations.
By leveraging these advanced indexing techniques, you can tailor your indexing strategy to the specific needs of your queries and data, ensuring optimal performance and efficiency in your PostgreSQL database.
Index usage tips and best practices
Effective use of indexes can significantly boost the performance of your PostgreSQL database. Here are some key strategies and best practices to help you make the most of your indexing capabilities.
Choose the right type of index
While we mentioned this earlier, it cannot be overstated— selecting the appropriate index type is crucial for optimizing query performance. Consider the nature of your queries and data types when choosing an index. B-tree indexes are versatile and suitable for most use cases, including equality and range queries. Hash indexes are beneficial for simple equality comparisons but are less flexible. For full-text searches, GIN indexes are ideal, while GiST indexes work well for geometric data. BRIN indexes are efficient for large tables with naturally sorted data, and SP-GiST indexes are optimal for multidimensional data.
Avoid common pitfalls
Over-indexing in PostgreSQL is a common mistake that can lead to increased storage requirements and slower write performance due to the overhead of maintaining multiple indexes. It’s essential to balance the need for indexes with the cost of maintaining them. Regularly review your indexes to ensure they are necessary and provide a performance benefit. Avoid creating indexes that are rarely used or that duplicate existing indexes without offering significant advantages.
Balancing indexes with write performance
While indexes improve read performance, they can negatively impact write performance due to the additional overhead of maintaining the index during insert, update, and delete operations. Carefully evaluate the trade-offs between read and write performance to ensure that the benefits of an index outweigh the costs. This is especially important in high-write environments where the impact of maintaining indexes can be more pronounced.
Indexing in a multi-tenant or partitioned environment
In multi-tenant or partitioned environments, indexing strategies need to be adapted to suit the specific architecture. For partitioned tables, consider creating local indexes on each partition to improve query performance without affecting global write operations. In multi-tenant setups, tailor indexes to the access patterns of each tenant to ensure efficient data retrieval across different segments of the database.
Understand and use partial indexes
Partial indexes are created with a condition that limits the index to a subset of the rows in a table. This can significantly reduce the size of the index and improve query performance for specific queries. Use partial indexes when queries frequently filter on a particular condition, allowing the database to quickly locate the relevant subset of data without scanning the entire index.
Leverage expression indexes and functional indexes
Expression indexes and functional indexes are powerful tools for optimizing queries that involve calculations or transformations on column values. By indexing the result of an expression or function, you can improve the performance of queries that would otherwise require on-the-fly computation. These indexes are particularly useful for complex queries where filtering or sorting is based on derived values. Ensure that the expressions or functions used in the indexes match those used in your queries to fully leverage the performance benefits.
Related: PostgreSQL Performance Tuning: Optimizing Database Parameters for Maximum Efficiency
Performance tuning with indexes
To effectively optimize queries, it is important to analyze their performance and understand how indexes can improve it. Begin by identifying slow-running queries and examining their execution patterns. Use indexing strategies tailored to the specific needs of these queries to reduce execution times. Consider both read and write operations to ensure that indexes provide a net performance benefit.
Using the EXPLAIN command to understand query execution plans
The EXPLAIN command in PostgreSQL is an invaluable tool for understanding how the database executes queries. By analyzing execution plans, you can see how indexes are used and identify potential bottlenecks. This insight allows you to make informed decisions about where to add or modify indexes to improve query performance.
Practical considerations for indexing
Indexing strategies for different workloads: Different workloads require different indexing strategies. For OLTP (Online Transaction Processing) systems, where fast read and write operations are critical, selective indexing that balances read and write performance is important. In contrast, OLAP (Online Analytical Processing) systems benefit from more extensive indexing to support complex queries and data analysis. Understanding the nature of your workload is key to selecting the appropriate indexing strategy.
Indexing for full-text search: Full-text search queries can be significantly accelerated using GIN indexes. These indexes allow efficient searching of large text fields by indexing the individual terms within the text. This is particularly useful for applications that involve searching through documents, logs, or other text-heavy data.
Indexing for spatial data types: Spatial data types, such as geographic and geometric data, require specialized indexing techniques to support efficient querying. SP-GiST indexes are well-suited for these types of data, enabling quick retrieval of spatial information based on location-based queries. This is essential for applications like mapping, geographic information systems (GIS), and location-based services.
PostgreSQL performance — and the bigger picture
Indexes are a fundamental part of PostgreSQL, critical to keeping queries fast and your database efficient. Choosing the right index type, avoiding common pitfalls, and staying on top of maintenance can go a long way toward steady performance.
But indexes are just one piece of the bigger picture. Running PostgreSQL in-house means your team is also on the hook for tuning, high availability, backups, upgrades, and security. Each of these adds to the workload, and many IT leaders find the hidden costs of DIY PostgreSQL catch up faster than expected.
If you’re wondering whether PostgreSQL is becoming more work than you bargained for, you’re not alone. Our guide, PostgreSQL in the Enterprise, breaks down the time, expertise, and resources enterprises often underestimate, and what that means for IT and the business.
isn’t hash index WAL-logged ever since PostgreSQL 10?