Cancelling database queries with context WithTimeout and WithCancel in Golang

We are going to halt all active queries with context by using two scenarios as listed below.

• If the query runs longer than 5 seconds.
  • This will be child context's responsibility which uses WithTimeout feature. The query will stop and produce context deadline exceeded error.


• If the application is crashed/stopped/cancelled (no matter how long the query runs for).
  • This will be parent context's responsibility which uses WithCancel feature. The query will stop and produce context canceled error.

As described above, we have a parent context for the whole application and a child context derived from the parent context. As a result:

• If the child context is cancelled, only the operations linked to it are affected. The parent context remains intact.


• If the parent context is cancelled, all the operations linked to it are affected. This includes all derived child contexts as well. Technically the whole application is affected.

Example

We are setting our parent context as HTTP server's BaseContext so it is be available for us throughout the request scope.

func main() {
    // Parent context.
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

    srv := &http.Server{
		Addr:    "some-address",
		Handler: "some-handler",
		BaseContext: func(listener net.Listener) context.Context {
			return ctx
		},
	}

    // ...
}

Make sure you grab the parent context from HTTP request and inject into where you run the query. Currently I am doing everything in the handler.

func myHandler(w http.ResponseWriter, r *http.Request) {
    // Grab the parent context.
    ctx := r.Context()
    
    // Create child context derived from the parent context.
    ctx, cancel := context.WithTimeout(ctx, 5 * time.Second)
    defer cancel()

    // Link the child context to the query.
    rows, err := DB.QueryContext(ctx, `some query`)
    // ...
}