magazine

Magazine

Excellent article about Magazine:

http://francescomari.github.io/2014/06/26/the-magazine-cache.html

Magazine is a least-recently used cache in JavaScript that divides a common cache into one or more individual collections.

Here is the basic usage.

// create a cache
var Cache = require('magazine')
var cache = new Cache

// create a magazine that stores to the cache
var magazine = cache.createMagazine()

// hold and release to key/value pairs to get them into the magazine
magazine.hold('one', { number: 1 }).release()
magazine.hold('two', { number: 2 }).release()

// wait a second
setTimeout(afterOneSecond, 1000)

function afterOneSecond () {
    // after a second hold and release one of the keys to refresh it
    magazine.hold('one', null).release()

    // wait another second
    setTimeout(afterTwoSeconds, 1000)
}

function afterTwoSeconds () {
    // after two seconds, purge anything that is older than a second and a half
    cache.expire(Date.now() - 1500)

    // hold the one cartidge, the given value is the default value to use if the
    // value does not exist in the cache.
    var cartridge = magazine.hold('one', { number: null })

    // check for a cache hit on one
    if (cartridge.value.number == null) {
        console.log('one is not in cache')
        cartridge.remove()
    } else {
        console.log('one is in cache')
        cartridge.release()
    }

    cartridge = magazine.hold('two', { number: null })

    // check for a cache hit on two
    if (cartridge.value.number == null) {
        console.log('two is not in cache')
        cartridge.remove()
    } else {
        console.log('two is in cache')
        cartridge.release()
    }
}

I created Magazine for use wtih Strata, a b-tree implementation in pure JavaScript. The b-tree implementation needs a cache for pages read from disk. Most applications that use Strata are going to want to use more than one b-tree, but why make the application developer have to think about tuning the page cache for each b-tree? So I created Magazine, a common cache has multiple collections.

new Cache

Create a new cache.

cache.expire(before).

Purge the cache removing items before the given date.

iterator = cache.purge()

Create an iterator over the cache in least recently used order.

magazine = cache.createMagazine()

Create a magazine using the cache.

magazine.expire(before)

Expire only the items in the current magazine.

cartridge = magazine.hold(key, value)

Hold a cartridge for the given key creating a cartridge if one does not exist.

cartridge.release()

Release the hold on the cartridge.

cartridge.remove()

Remove the hold the cartridge. You must be the only one holding it to remove it.

cartridge.adjustHeft(value)

Adjust the heft of the cartridge. Heft is some arbitrary measure of the weight of cartridge. For cached managed by count, the actual count of items might not be a the cache entry itself. The cache entry could contain an array of items, for example, and user wants to purge the cache when it has more than a total number of items.

cartridge.heft

An arbitrary measure of the weight of the cartridge.

purge.next()

Move to the next oldest entry in the queue.

purge.release()

Releases a cartridge if one is held, a safe way to finalize a purge iteration.