This paper describes the design of a crawler devised to perform the periodic retrieval of Web documents for a search engine able to accept on-line updates in a concurrent manner On-line updates comes in the form of insertions of new documents or update of existing ones, all of them mixed with the usual user queries. The search engine is bulk-synchronous which allows it to deal efficiently with the concurrency control problem. The crawler is also bulk-synchronous so that it can be integrated into the same P-processors cluster executing the search engine. This paper describes and evaluates the practical feasibility of such a crawler.