Add Redis Caching

[mgutz]

Implement caching using Redis.

type Cacher interface {
   // Cache caches the result of a Select or SelectDoc. If id is not provided, an FNV checksum
   // of the SQL is used as the id. (If interpolation is set, arguments are hashed). Use invalidate to 
   // immediately invalidate the cache to force setting its value.
    Cache(id string, duration time.Duration, invalidate bool)
}

// cache pre-defined game information for a week
DB.SelectDoc("*").
     From("games").
     Cache("games", 7 * 24 * time.Hour, false).
     QueryStruct(&games)

// cache user information for 30 seconds
DB.SelectDoc("*").
     From("users").
     Where("user_id = $1", id).
     Cache("", 30 * time.Second, false).
     QueryStruct(&user)

// invalidates cache for key "games"
DB.InvalidateCache("games")

// invalidates all 
DB.InvalidateCache(")

[elithrar]

Neat idea. I assume the implementation of Cache is to fall back to querying directly if the hash of the query (or query + args) does not exist in Redis?

I'd be curious to see the benchmarks for a "big set of cached results from Redis" vs. "big set of cached results from the DB" (given that Postgres caches too).

[mgutz]

Correct, the cache will get updated:

• entry does not exist (either new entry or redis expired it)
• invalidate is true