Why is database/sql in Go Slower than Directly Querying Postgres?

Querying Using database/sql Slower than Direct Querying to Postgres

When querying a local Postgres instance using a Go application, there can be a noticeable performance difference between using database/sql and querying the database directly. This question explores the potential causes behind this discrepancy.

Background Information

The database/sql package provides an interface for interacting with SQL databases. It manages a pool of connections to the database, and each connection can be used to execute multiple queries. However, it's crucial to understand the handling of connections when using database/sql.

• Connection Pool: sql.DB represents a pool of connections, not a single connection. The pool can be configured with options such as the maximum number of connections and the maximum lifetime of connections.
• Lazy Connection Opening: When you open a connection using sql.Open, the actual connection establishment may not happen immediately. The pool lazily opens connections as needed.

Explanation of Performance Difference

The main reason for the performance difference is that:

1. Establishing New Connections:

• The first db.Query is relatively slow because it involves establishing a new connection to the database.
• The second db.Query is slightly slower because the pool opens a new connection instead of reusing the connection from the first query.

Solution:

To eliminate the performance hit caused by establishing new connections, it's recommended to:

• Release Connections Back to the Pool: After completing each query, close the rows object returned by db.Query. This releases the associated connection back to the pool.
• Pre-initialize the Pool: After opening the pool, call db.Ping to force the establishment of at least one connection before executing any queries. This ensures that there will be an available connection for the first query.

With these optimizations, the performance of database/sql queries can be significantly improved.

Note on Prepared Statements:

If your queries involve any arguments, it's important to note that database/sql actually creates and executes a prepared statement under the hood. Prepared statements provide efficiency benefits, but they also involve some overhead, especially for simple queries with no arguments.

By understanding the connection management and prepared statement behavior of database/sql, you can optimize your queries for performance and eliminate significant slowdowns.

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