Golang API のキャッシュ戦略と最適化

package api

import (
    "context"
    "database/sql"
    "fmt"
)

// User represents a user in the system.
type User struct {
    ID   int64
    Name string
}

// GetUserInfo retrieves user information from the database.
func GetUserInfo(ctx context.Context, db *sql.DB, userID int64) (*User, error) {
    row := db.QueryRowContext(ctx, "SELECT id, name FROM users WHERE id = ?", userID)
    var user User
    if err := row.Scan(&user.ID, &user.Name); err != nil {
        return nil, fmt.Errorf("failed to scan user: %w", err)
    }
    return &user, nil
}

package api

import (
    "context"
    "database/sql"
    "fmt"
    "sync"
    "time"

    "github.com/golang/lru"
)

// Cache holds a LRU cache for user information.
type Cache struct {
    mu    sync.RWMutex
    cache *lru.Cache
}

// NewCache creates a new LRU cache with a maximum size of 100 entries.
func NewCache() (*Cache, error) {
    cache, err := lru.New(100)
    if err != nil {
        return nil, fmt.Errorf("failed to create LRU cache: %w", err)
    }
    return &Cache{cache: cache}, nil
}

// GetUserInfo retrieves user information from the database or cache.
func (c *Cache) GetUserInfo(ctx context.Context, db *sql.DB, userID int64) (*User, error) {
    c.mu.RLock()
    user, ok := c.cache.Get(userID)
    c.mu.RUnlock()

    if ok {
        return user.(*User), nil
    }

    c.mu.Lock()
    defer c.mu.Unlock()

    user, err := GetUserInfo(ctx, db, userID)
    if err != nil {
        return nil, err
    }

    c.cache.Add(userID, user)
    return user, nil
}