Memis

Installation

Using npm:

npm install -S memis

Usecase

Your application should be fault-tolerant. Availability is not guaranteed and all data is eventual consistent. Memis does not guarantee that updates are successfully propogated to all subscribers. It is used for constant rates of updates (specifically: no intended to be used to replicate user content).

Examples of usecases are:

• configuration of non-mission-critical parameters (A/B testing).
• sharing small numbers of log messages (e.g. status updates) between servers.

Usage

First, require memis and create a client:

var memis = require('memis'),
	client = memis.createClient();

Note that createClient takes the same arguments as the default redis client (i.e. host, port, etc.).

In memis, the key/value domain is seperated in three different levels: databases, collections and items.

You can use databases if you want to replicate multiple collections that belong to eachother. For example, I use a database for each region that my code runs for. Note that you cannot replicate an entire database.

Instead, you select one or multiple collections in a single database:

var db = client.database("region-nl"),
	artists = db.collection("artists"),
	albums = db.collection("albums");

Subscribing

First of all, you start by adding event listeners for these three events:

• set is called when a new key is added to the collection or when the contents of that key are changed. Note that we may or may not emit this event when the contents are .set(...) by another instance but the contents have not changed.
• expire is called when a key is expired (see the ttl param of .set(...)). This is a best-effort operation and you should not expect this event to be exactly on time. See: Timing of expired events.
• delete is called when a key is deleted (by a del operation). Note that del operations are not (yet) implemented by memis.

artists.on('set', function(key, data) {
	/* New / updated artist. */
});

artists.multi('expire delete', function(key, data) {
	/* Expired / deleted artist. Data is the last cached copy. */
});

You then proceed by subscribing to each of those collections:

artists.subscribe();
albums.subscribe();

Note that you cannot provide a callback.

Publishing

You do not have to subscribe to a collection in order to be able to publish items.

Note that you can only publish objects. You cannot publish other structures (strings, integers, arrays) directly. Memis stores all items as hashes.

The last argument is an optional int that specifies the time to live in seconds for the item.

artists.set('coldplay', {
	genre: 'Alternative'
}, 3600 * 24);