Today we continue to review the paper Queues are Databases by Jim Gray.
 He talks about message oriented middleware (MOM) and made the observation that queues are better inside the database for transactions. When queues are outside database, they pose performance and concurrency control problems. The mechanisms for concurrency control within a database include Read_Past, Read_Through, Notify,
Read_Past allows skipping over dirty records to find the first committed record and is used in dequeue(). Read_Through allows a program to examine records that have not yet been committed. Notify allows a program to wait for the state change in a lock.
Queue managers are simple TP-monitors
Queues may have workerpools associated with them. This helps to service the entries in the queue. TP monitors configure, manage and load balance these pools. Queued processing has many variants. These include periodic, event and batch. Queues may also have a scheduling policy.
When the queues are implemented as part of the database, triggers may be invoked to give a simple queued transaction processing system.
Queue managers can be built in an Object Relational database system
#coding exercise
Implement promises on message queues.
function promise ( function (resolve, reject){

});
The constructor sends a message to the queue
The callback receives a message from the queue.