Is a Single mgo.Session Sufficient for Concurrent Use in a Go Web Application?

Concurrency Considerations in MongoDB with gopkg.in/mgo.v2

When integrating MongoDB into a Go web application using gopkg.in/mgo.v2, it is essential to consider concurrency best practices for optimal performance and resource utilization. This article addresses the following question:

Can a single mgo.Session be used concurrently within a web application, such as in an http.Handler, or should Session.Copy and Session.Close be employed to create a pool of sessions instead?

Explanation:

The mgo.Session, contrary to initial assumptions, is indeed safe for concurrent use. As stated in the official documentation, "All Session methods are concurrency-safe and may be called from multiple goroutines."

However, this does not imply that using only one mgo.Session in a concurrent setting is advantageous. Sessions automatically manage a pool of connections, but utilizing a single Session limits the ability to leverage multiple connections simultaneously and potentially distribute across server nodes if available.

Creating new Sessions for each request, copying them if necessary, and closing them properly (using Session.Close with defer) allows for optimal resource utilization. By managing multiple connections, the system can potentially use more connections and server nodes concurrently, resulting in faster response times for both the database and end-users.

Session.Close does not terminate the underlying connection to the server but rather returns it to the pool, making it available for other sessions to pick up.

For further insights, refer to the related discussion on the performance of Sessions: mgo - query performance seems consistently slow (500-650ms).

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