Description of Asynchronous processing in Salesforce

Asynchronous processes are requests that do not execute immediately at the time they are submitted, but instead execute separately, one at a time from a queue. In computing, a message queue stores all requests from different systems to ensure each request is processed in the order received. Salesforce uses the same queue-based asynchronous processing architecture. Each asynchronous request is placed in the queue, stored for recovery reasons, and de-queued for execution across multiple organizations within each instance. Because many customers share available resources on each Salesforce instance, the exact execution timing of asynchronous requests cannot be predicted or guaranteed.