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Golang / GoLang Production Patterns and Web Standards Interview Questions

How do you implement timeouts for non-HTTP operations like database queries and external calls?

Context-based timeouts apply to any blocking operation — database queries, cache lookups, file operations, and external gRPC calls. The pattern is identical: create a child context with a deadline and pass it to every blocking call.

// Database query with timeout
func getUserFromDB(ctx context.Context, db *sql.DB, id int) (*User, error) {
    // Add query-level timeout (in addition to any HTTP request timeout)
    ctx, cancel := context.WithTimeout(ctx, 2*time.Second)
    defer cancel()

    row := db.QueryRowContext(ctx,
        "SELECT id, name, email FROM users WHERE id = $1", id)

    var u User
    if err := row.Scan(&u.ID, &u.Name, &u.Email); err != nil {
        if errors.Is(err, context.DeadlineExceeded) {
            return nil, fmt.Errorf("DB query timed out after 2s: %w", err)
        }
        return nil, fmt.Errorf("getUserFromDB: %w", err)
    }
    return &u, nil
}

// Multiple operations with individual timeouts
func getUserProfile(ctx context.Context, userID int) (*Profile, error) {
    // DB: 2s timeout
    dbCtx, dbCancel := context.WithTimeout(ctx, 2*time.Second)
    defer dbCancel()
    user, err := getUserFromDB(dbCtx, db, userID)
    if err != nil { return nil, err }

    // Cache: 500ms timeout
    cacheCtx, cacheCancel := context.WithTimeout(ctx, 500*time.Millisecond)
    defer cacheCancel()
    prefs, _ := getPrefsFromCache(cacheCtx, userID) // non-fatal if cache misses

    // External API: 3s timeout
    apiCtx, apiCancel := context.WithTimeout(ctx, 3*time.Second)
    defer apiCancel()
    avatar, err := fetchAvatarFromCDN(apiCtx, user.AvatarURL)
    if err != nil {
        log.Printf("avatar fetch failed (non-fatal): %v", err)
    }

    return buildProfile(user, prefs, avatar), nil
}

What is the effective deadline when you create a 5-second timeout on a child context whose parent already has a 3-second deadline?
When errors.Is(err, context.DeadlineExceeded) returns true in a database query, what does it indicate?

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