How to Manage Database Timeouts and Cancellations in Go

Here mainly introduces the context of request, but there are a few points to note. If you use middleware, you will require all requests to be processed. Do you need this? Also pay attention to the writetimeout of resp, otherwise if the timeout of the request in sql processing is greater than w, it is basically invalid.

 

Not processed, first create a conditional sql

package main

import (
    "database/sql"
    "fmt"
    "log"
    "net/http"

    _ "github.com/lib/pq"
)

var db *sql.DB

func slowQuery() error {
    _, err := db.Exec("SELECT pg_sleep(10)")
    return err
}

func main() {
    var err error

    db, err = sql.Open("postgres", "postgres://user:pa$$word@localhost/example_db")
    if err != nil {
        log.Fatal(err)
    }

    if err = db.Ping(); err != nil {
        log.Fatal(err)
    }

    mux := http.NewServeMux()
    mux.HandleFunc("/", exampleHandler)

    log.Println("Listening...")
    err = http.ListenAndServe(":5000", mux)
    if err != nil {
        log.Fatal(err)
    }
}

func exampleHandler(w http.ResponseWriter, r *http.Request) {
    err := slowQuery()
    if err != nil {
        serverError(w, err)
        return
    }

    fmt.Fprintln(w, "OK")
}

func serverError(w http.ResponseWriter, err error) {
    log.Printf("ERROR: %s", err.Error())
    http.Error(w, "Sorry, something went wrong", http.StatusInternalServerError)
}

 

 

Several processing demos

package main

import (
    "context" // New import
    "database/sql"
    "fmt"
    "log"
    "net/http"
    "time" // New import

    _ "github.com/lib/pq"
)

var db *sql.DB

func slowQuery(ctx context.Context) error {
    // Create a new child context with a 5-second timeout, using the
    // provided ctx parameter as the parent.
    ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
    defer cancel()

    // Pass the child context (the one with the timeout) as the first
    // parameter to ExecContext().
    _, err := db.ExecContext(ctx, "SELECT pg_sleep(10)")
    return err
}

...

func exampleHandler(w http.ResponseWriter, r *http.Request) {
    // Pass the request context to slowQuery(), so it can be used as the 
    // parent context.
    err := slowQuery(r.Context())
    if err != nil {
        serverError(w, err)
        return
    }

    fmt.Fprintln(w, "OK")
}

...

 

 

package main

import (
    "context"
    "database/sql"
    "errors" // New import
    "fmt"
    "log"
    "net/http"
    "time"

    _ "github.com/lib/pq"
)

var db *sql.DB

func slowQuery(ctx context.Context) error {
    ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
    defer cancel()

    _, err := db.ExecContext(ctx, "SELECT pg_sleep(10)")
    // If we get a "pq: canceling statement..." error wrap it with the 
    // context error before returning.
    if err != nil && err.Error() == "pq: canceling statement due to user request" {
        return fmt.Errorf("%w: %v", ctx.Err(), err)
    }

    return err
}

...

func exampleHandler(w http.ResponseWriter, r *http.Request) {
    err := slowQuery(r.Context())
    if err != nil {
        // Check if the returned error equals or wraps context.Canceled and 
        // record a warning if it does.
        switch {
        case errors.Is(err, context.Canceled):
            serverWarning(err)
        default:
            serverError(w, err)
        }
        return
    }

    fmt.Fprintln(w, "OK")
}

func serverWarning(err error) {
    log.Printf("WARNING: %s", err.Error())
}

...

 

 

...

func main() {
    var err error

    db, err = sql.Open("postgres", "postgres://user:pa$$word@localhost/example_db")
    if err != nil {
        log.Fatal(err)
    }

    // Create a context with a 10-second timeout, using the empty 
    // context.Background() as the parent.
    ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
    defer cancel()

    // Use this when testing the connection pool.
    if err = db.PingContext(ctx); err != nil {
        log.Fatal(err)
    }

    mux := http.NewServeMux()
    mux.HandleFunc("/", exampleHandler)

    log.Println("Listening...")
    err = http.ListenAndServe(":5000", mux)
    if err != nil {
        log.Fatal(err)
    }
}

...

 

middleware

func setTimeout(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
        defer cancel()

        // This gives you a copy of the request with a the request context 
        // changed to the new context with the 5-second timeout created 
        // above.
        r = r.WithContext(ctx)
        next.ServeHTTP(w, r)
    })
}

 

 

Original address

https://www.alexedwards.net/blog/how-to-manage-database-timeouts-and-cancellations-in-go

 

The author wrote very detailed, the content is not difficult.