1. In a publish/subscribe system having one or more subscribers subscribing to data from one or more data sources, a just-in-time publish/subscribe messaging system comprising: a first table for recording in real time, the data sources existing in the system; a second table for recording user subscirptions for the data sources subscribed to by the user subscribers; a subscription process preventing a subscribed to data source recorded in said first table as being available from delivering messages to user subscribers if the number of user subscriptions in said second table for that data source does not exceed a predetermined number; a monitoring process for monitoring in real time, user subscriptions from user subscribers and recording in said second table the user subscriptions for each data source in the system such that there is real-time collection of user subscriptions for data from said available data sources; a data source registry in said first table for recording the availability of each data source having data for transmission to said user subscribers, and a matching routine turning off any data source process associated with a data source if that data source has not been subscribed to by said user subscribers more that a predetermined number of times, such that messages from a data source associated with a turned off data source process may not transmit messages to the user subscribers.