What is PgBouncer in the PostgreSQL Database? Find out now! 🤔

Q: What is PgBouncer in PostgreSQL?

PgBouncer is an important connection pool for the Postgres database and helps to optimize database connections; PgBouncer also enhances performance by efficiently managing connections, making it a valuable tool for scalability and resource utilization.

Q: What license is PgBouncer released under?

PgBouncer has been released under the open source ISC License -- find the PgBouncer license on GitHub here.

Q: Why use PgBouncer?

PgBouncer helps to improve the scalability, performance, and resource management of PostgreSQL database connections in applications with high concurrency and connection requirements and is especially valuable in scenarios where the number of database connections needs to be controlled and optimized efficiently.

PgBouncer is an important open-source connection pool middleware component for the Postgres database and helps to optimize database connections; PgBouncer also enhances performance by efficiently managing connections, making it a valuable tool for scalability and resource utilization.

PgBouncer acts as an intermediary between client applications and PostgreSQL database servers and is important to database development because it efficiently manages connection pooling thereby reducing resource strain and improving performance for PostgreSQL applications.

This article was updated on June 19, 2025 — refer to the database development category page for similar articles and tutorials.

Why use PgBouncer?

Below I’ve included a graphic illustrating what a hypothetical PgBouncer to PostgreSQL database architecture might look like (this is not complete — for example, this graphic is missing load balancers).

Here are several key features and functions of Pg_Bouncer that should provide some compelling reasons for including this middleware in your software development effort:

Connection Pooling

PgBouncer maintains a pool of database connections, thereby allowing multiple client applications to share and reuse connections to Postgres.

PgBounce’s DB connection pooling capabilities help to reduce the overhead of establishing and tearing down connections for each database request thereby improving efficiency as well as performance.

A database connection pool, such as PgBouncer, is an important middleware component in software development projects, primarily used to efficiently manage database connections in high-traffic applications.

A database connection pool maintains a cache of open database connections that can be quickly reused, significantly reducing the overhead associated with opening and closing connections for each user request.

This feature is especially beneficial in scenarios with frequent, short-lived database interactions, such as in web applications, where it ensures smoother, faster database access while minimizing resource consumption.

By managing the number of active connections and distributing the workload effectively, connection pools enhance application performance, provide better scalability, and ensure more stable interaction with the database, making them indispensable for maintaining optimal database performance and reliability.

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Connection Pool Management

The PgBouncer’s primary purpose is to act as a connection pool to the Postgres database.

PgBouncer controls the number of concurrent connections to the Postgres database thereby ensuring that the database server is not overwhelmed by a connection spike.

PgBounce can be configured such that limitations are placed on the number of connections for each database user or pool.

Pg Bounce supports three connection rotation strategies which are described on the features section of the PgBouncer.org website — these strategies include session pooling, statement pooling, and transaction pooling.

Refer to the table under the section entitled SQL feature map for pooling modes on the PgBouncer website that details several Postgres features and whether or not they’re compatible with the given PgBouncer pooling mode.

In the following sections I’m going to detail the use cases for session, transaction, and statement pooling strategies.

Session Pooling Use Case

Session pooling in PgBouncer is particularly useful for web applications where users maintain persistent sessions, such as in online shopping platforms or banking applications.

These applications often rely on session-specific settings or temporary data stored in the database, like user preferences or shopping cart contents.

In session pooling, a single database connection is maintained for the entire duration of a user’s session, ensuring that all session-level settings and temporary data are preserved across multiple transactions.

This mode of pooling is ideal for scenarios requiring long-lived transactions or complex, multi-step operations.

In an e-commerce site, for example, as a user interacts with their shopping cart, session pooling ensures that all additions and deletions to the cart are consistently reflected, as each interaction occurs over the same database connection.

This continuous connection is important for applications where the sequence and state of transactions are important.

While session pooling may not be as efficient as transaction pooling for short-lived transactions, it offers significant benefits by reducing the overhead of establishing new connections for each user session.

Session pooling is a suitable choice for applications where the consistency and continuity of the database session are more important than maximizing the reuse of connections for brief transactions.

Transaction Pooling Use Case

Transaction pooling is particularly useful for read-heavy workloads due to the efficient reuse of connections for short-lived transactions.

Transaction pooling in PgBouncer is well suited for high-volume environments with numerous short-lived transactions (web applications tend to fit this description), where the connection pooler efficiently reuses database connections in order to maximize resource utilization and reduce the overhead of establishing new connections.

Transaction pooling is most effective for stateless transactions, where each operation can be executed independently without relying on previous session-specific states, making PgBouncer less suitable for scenarios involving long-running transactions or applications that require persistent session-level settings.

We’ll take a look at statement pooling next.

Statement Pooling Use Case

Statement pooling in PgBouncer is a specialized and restrictive mode of connection pooling, particularly suitable for high-security environments such as financial systems or applications handling sensitive data.

In statement pooling mode, each database connection from the pool is used exclusively for the duration of a single SQL statement, and then immediately returned to the pool.

Returning the connection to the pool ensures heightened security and consistency, as no residual data or session states are carried over from one statement to the next, thereby significantly reducing the risk of session-state abuse and potential data leaks.

The statement pooling strategy is ideal for applications that operate in a highly stateless manner, where interactions with the database do not require the persistence of session data between queries.

When the PgBouncer is configured to use statement pooling, each query is treated as a completely independent operation, eliminating the reliance on previous states.

Statement pooling is particularly important when the workload consists mostly of simple, independent, and quick queries, as it maximizes connection efficiency under these specific conditions.

In environments where strict control over database interactions is crucial, statement pooling in PgBouncer provides an essential layer of security.

By isolating each SQL statement execution within its own connection, it ensures that any operational context is tightly contained, making it an invaluable tool for scenarios demanding the highest level of data integrity and security.

Authentication

PgBouncer can handle the authentication of client connections thereby providing an additional layer of database security.

PgBounce can be configured to authenticate users against a PostgreSQL user database or use its own user authentication mechanism.

Load Balancing

PgBouncer can distribute incoming database requests among multiple PostgreSQL servers (either primary and standby or different databases) to balance the load and improve database performance.

Connection String Rewriting

PgBouncer can rewrite and modify connection strings to match the settings of pooled connections to postgresql, ensuring that client applications connect to the database using the appropriate settings.

Idle Connection Management

PgBouncer can manage idle connections by gracefully closing and releasing connections that are no longer in use, preventing resource wastage.

Query Buffering

Pg Bouncer can buffer and queue queries when all available connections are in use thereby preventing clients from waiting in line for a connection to become available.

See the pool_mode section of the Pg Bounce configuration file specification.

High Availability

For failover and high availability scenarios, Pg Bouncer can be used in conjunction with PostgreSQL replication solutions.

See the discussion entitled PostgreSQL High Availability/Scalability using HAProxy and PGBouncer on StackExchange.

Another article which worth a read is entitled Taking Advantage of write-only and read-only Connections with pgBouncer in Django.

Article Conclusion

In the process of engineering this content I came across the AWS Labs pgbouncer-fast-switchover project on Github.

The pgbouncer-fast-switchover project is open-source software based on pgbouncer, which adds three new significant features: client query rewrites, query routing, and fast switchovers of readers and writers.

Learn more about database change notifications — a powerful feature supported by some relational databases as well as the video on Scaling Postgres Beyond PostgreSQL PgBouncer & Postgres Pgpool-II: Advanced Traffic Management.

Frequently Asked Questions (FAQ)

What license is PgBouncer released under?

PgBouncer has been released under the open-source ISC License — find the PgBouncer license on GitHub here.

What is a database connection pool?

A database connection pool, such as PgBouncer for Postgres, is middleware that manages database (DB) connections efficiently. A DB connection pool keeps a cache of open connections that can be reused for requests to the database, and which reduces the time and resources needed to open and close connections for each operation. Using a DB connection pool typically speeds up database operations, helps to better manage the load on the database server, and simplifies the process of managing connections for developers.

Why use PgBouncer?

PgBouncer helps improve the scalability, performance, and resource management of PostgreSQL database connections in applications with high concurrency and connection requirements and is especially valuable in scenarios where the number of database connections needs to be controlled and optimized efficiently. For more details along with a description of various features provided by PgBouncer can be found under the section of the article that answers this question in more detail.