1. A method, implemented on a machine having at least one processor, storage, and a communication platform connected to a network for document update in a database, comprising: obtaining information related to document update in the database; generating a stochastic model based on the obtained information; determining an update sequence based on the stochastic model, wherein the update sequence indicates at least one document that needs to be updated in a time slot; retrieving one or more documents from the database based on the update sequence; and updating the retrieved one or more documents in the time slot.