Why Am I Getting 'Accept error: accept tcp [::]:80: accept4: too many open files' in my Go MongoDB Server?

Too Many Open Files in mgo Go Server

When encountering the error "Accept error: accept tcp [::]:80: accept4: too many open files," in a MongoDB server written in Go using mgo, it indicates that the maximum number of simultaneous file descriptors has been reached. This error suggests that something is potentially being opened and not closed on every request.

Solution

The fundamental issue lies in the incorrect usage of MongoDB connections. Instead of storing an mgo.Database instance, it is essential to store an mgo.Session. When interacting with MongoDB, always acquire a copy or clone of the session and diligently close it when not needed. This approach ensures that connections are not leaked.

Furthermore, it is crucial to thoroughly check for errors in all database operations. Printing or logging errors is the minimum step to take when an error occurs.

Code Sample

Below is an improved code sample that addresses these issues:

var session *mgo.Session

func init() {
    var err error
    if session, err = mgo.Dial("localhost"); err != nil {
        log.Fatal(err)
    }
}

func someHandler(w http.ResponseWriter, r *http.Request) {
    sess := session.Copy()
    defer sess.Close() // Must close!

    c := sess.DB("mapdb").C("tiles")
    // Do something with the collection, e.g.
    var tile bson.M
    if err := c.FindId("someTileID").One(&result); err != nil {
        // Tile does not exist, send back error, e.g.:
        log.Printf("Tile with ID not found: %v, err: %v", "someTileID", err)
        http.NotFound(w, r)
        return
    }
    // Do something with tile
}

By implementing these modifications, the code effectively manages connections and ensures that they are properly closed. This resolves the issue of too many open files and improves the overall performance of the MongoDB server.

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