Memcached Transactions

Memcached Transactions is a wrapper around node-memcached. It provides an isolated transactional environment for all-or-nothing writes, and smart caching of previously received, written and deleted data.

This does not magically alter the behavior of Memcached. It simply queues up all your mutating operations until you are sure you want to do them at all. Only when you choose to "commit" will all operations be executed (one by one).

Example

var Memcached = require('memcached');
var MemcachedTransaction = require('memcached-transactions');

var client = new Memcached(['localhost:11211']);
var tr = new MemcachedTransaction(client);

tr.set('foo', 5);
tr.get('foo', function (error, value) {
	console.log(value); // outputs 5, even though nothing has been written yet

	tr.set('foo', value + 1);

	// commit changes to memcached

	tr.commit(function (error) {
		tr.del('foo');
		tr.commit();
	});
});

Outputs foo 6. Note that foo was never set to 5 in memcached. Only on commit do values ever get created, deleted or updated.

API

The API tries to follow node-memcached to the letter. The only differences are:

new MemcachedTransaction(memcachedClient, [options])

Where options is an optional object containing:

simulate (boolean)

If true does not write anything to the memcached server on commit, but instead outputs all scheduled operations to console. This way operation bundling and discarding can be inspected for correctness.

debug (boolean, function)

If true outputs every memcached operation to console. If debug is a function, that function will be called (with a variable number of arguments) whenever debug information is output.

myTransaction.commit([cb])

Executes all scheduled write operations. On completion, the optional callback cb is called.

myTransaction.rollBack([cb])

Discards all scheduled write operations and calls the optional callback cb on completion. This function is however not asynchronous, so the callback may safely be omitted. It is simply provided as a convenient exit point that is similar to the callback in the commit function.

API: transactional node-memcached wrappers

The following wrapper functions are available. General rule is that write functions are queued and merged for commit, and read functions only read that what has not yet been retrieved or overwritten within this transaction.

myTransaction.get(key, [cb])

myTransaction.getMulti(keys, [cb])

myTransaction.set(key, value, [ttl, cb])

Since writes are queued, the callback cb is provided only for compatibility.

myTransaction.del(key, [cb])