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AutoHot

This is a demonstration of a lightweight in-memory caching pattern I learned at Gravity. This version is quite simple though. It uses Akka for scheduling and ehCache for caching.

The idea is that simply by wrapping a call to a cache-worthy piece of code (like a DB call or API call or anything that adds latency) you can have that code execute on a background thread and refresh its value in the cache. Then when you retrieve it you know you've already got a version that's no older than the refresh time.

Usage

There's currently only one method, heat. The first parameter list configures the label (used as a key in the cash and for logging) and refresh frequency. The second parameter list is a thunk (function that takes no parameters and returns a value). The value is stored in the cache as well as returned from the call to heat.

Due to the magic of closures, the calling context remains in scope on future calls

def getConfigurationFromDB(dbService: DbService) = {

    dbService.oneTimeConfiguration(some, parameters)

    AutoHot.heat("example", 5.minutes){
        dbService.fetch(configurationTable)
    }
}

The above example will allow you anywhere you can call getConfigurationFromDB to always have values that are no more than 5 minutes old. This is great for data that doesn't change too frequently, and when there are only a few unique queries (that's actually a lot of cases!)

Don't use it like you would an LRU cache, because it doesn't automatically evict older entries when it fills up. Best used for long running, one-off queries such as configuration values.

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Lightweight auto-reloading caching pattern for Scala

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