How will Redis and Postgres synchronize? They can diverge.

Redis and Postgres can diverge because Redis is often used as a cache, while Postgres serves as the primary data store. To synchronize them, several approaches are used:

• Write-through cache: data is first saved in Postgres, then Redis is updated. This ensures consistency but may slow down write operations.
• Cache invalidation: when data in Postgres changes, a signal (such as through an event or queue) is sent to clear or update the corresponding entries in Redis.
• TTL (time to live): cached data in Redis has a limited lifespan, after which it is refreshed from Postgres.

Example of simple cache update after writing to the database in Go:

// Update data in Postgres
err := updatePostgres(data)
if err != nil {
    return err
}
// Update cache in Redis
err = redisClient.Set(ctx, key, serializedData, 0).Err()
if err != nil {
    // Log the error, but data in Postgres is already updated
}

It is important to choose a strategy based on the requirements for consistency and performance.